Liquid sample holder and performing magnetometry measurements

Abstract

A liquid sample holder for magnetometry measurements includes: a cylindrical sample space for receiving a liquid sample, the sample space having a first end and a second end; a hollow extension extending from the first end of the sample space, the hollow extension having an internal diameter substantially equal to an internal diameter of the sample space; a hollow extension extending from the second end of the sample space, the hollow extension having an internal diameter substantially equal to the internal diameter of the sample space; an elastomer septum sealing the sample space; and a rigid cover sealing the elastomer septum.

Description

LIQUID SAMPLE HOLDER AND PERFORMING MAGNETOMETRYMEASUREMENTSSTATEMENT REGARDING FEDERALLY SPONSORED RESEARCH

[0001] This invention was made with United States Government support from the National Institute of Standards and Technology (NIST), an agency of the United States Department of Commerce. The Government has certain rights in this invention.CROSS-REFERENCE TO RELATED APPLICATION

[0002] This application claims the benefit of U.S. Provisional Patent Application Serial No. 63 / 699,960 (filed 9 / 27 / 2024), which is herein incorporated by reference in its entirety.BACKGROUND

[0003] The present invention generally relates to the field of liquid sample holders for magnetometry measurements, and more particularly to techniques for minimizing measurement artifacts caused by the fluid nature of samples during magnetometry analysis.

[0004] The field of magnetometry involves measuring the magnetic properties of materials. These measurements are crucial for understanding the behavior of magnetic materials and for developing new technologies that utilize magnetism. Accurate magnetometry measurements require precise control over the sample environment to minimize artifacts that can arise from the sample itself or its surroundings.

[0005] Conventional liquid sample holders for magnetometry often suffer from several drawbacks. One significant issue is sample movement duringmeasurement. Due to the fluid nature of the sample, its shape, center position, and particle distribution can shift in response to the applied magnetic field. These changes can lead to inaccurate magnetic moment measurements and introduce artifacts into the hysteresis loop data. Another problem is the potential for air bubbles to become trapped in the sample space, which further exacerbates sample movement and introduces additional artifacts.

[0006] Furthermore, conventional holders often fail to adequately address the magnetic signals arising from the holder itself. The geometry of the holder can create end effects, contributing to an inhomogeneous magnetic background and obscuring the signal from the sample. Additionally, the materials used to construct the holder may possess their own magnetic moments, further interfering with the measurement. Finally, the sealing process itself can immobilize some of the magnetic particles in the sealant, leading to a heterogeneous sample and potentially impacting the measured magnetic moment.

[0007] It is therefore an objective of the present invention to provide a liquid sample holder design that minimizes sample movement, reduces artifacts arising from the holder geometry and materials, and prevents particle immobilization during sealing, thereby overcoming the above-mentioned disadvantages of the prior art at least in part.

[0008] Accordingly, methods and equipment for preparing and analyzing liquid samples in magnetometry measurements that minimize measurement artifacts would be advantageous and would be favorably received in the art.BRIEF DESCRIPTION

[0009] One aspect of the present invention relates to a liquid sample holder for magnetometry measurements. A liquid sample holder can be understood as a container specifically designed for holding fluid samples during analysis in a magnetometer. Magnetometry measurements involve the determination of a sample’s magnetic properties, such as its magnetic moment, in response to an applied magnetic field or temperature.

[0010] It can be provided that the liquid sample holder comprises a cylindrical sample space for receiving a liquid sample. This arrangement provides a well-defined geometry for the sample, minimizing shape-related distortions in the magnetic field that can lead to measurement errors. One advantage of this cylindrical design is its compatibility with existing sample handling and mounting systems of commercial magnetometers.

[0011] It may further be provided that the cylindrical sample space has a first end and a second end. This arrangement provides clearly defined boundaries for the sample volume, contributing to the consistent positioning needed for precise magnetometry measurements.

[0012] It may also be provided that the liquid sample holder comprises a hollow extension extending from the first end of the sample space. This arrangement helps reduce spurious magnetic signals, often referred to as end effects that can arise from the boundaries of the sample holder as it moves through the detection coils of the magnetometer. One advantage of employing a hollow extension is that it minimizes the holder’s thermal mass, facilitating faster temperature stabilization during measurements.

[0013] It may also be provided that the liquid sample holder comprises a hollow extension extending from the second end of the sample space, similar to the hollow extension on the first end. By maintaining consistent internal dimensions throughout the length of the holder, this arrangement further minimizes end effects and reduces thermal mass, enabling faster and more accurate temperature control during analysis.

[0014] It may also be provided that the liquid sample holder comprises an elastomer septum sealing the sample space. This arrangement enables the complete filling of the sample space without trapping air bubbles while preventing any particles from becoming immobilized in the seal during the closing process. One advantage of using an elastomer septum is its ability to self-seal after sample injection, minimizing the potential for contamination and enabling preparation of air-sensitive samples.

[0015] It may also be provided that the liquid sample holder comprises a rigid cover sealing the elastomer septum. This arrangement adds structural integrityto the holder, preventing deformation or leakage of the sample, especially under vacuum conditions or during temperature changes. One advantage of this design is its ability to maintain a consistent sample geometry even during thermal cycling, enabling accurate measurements over a wide temperature range.

[0016] One aspect of the present invention relates to a method of performing magnetometry measurements of a liquid sample. Magnetometry measurements can be understood as techniques for determining the magnetic properties of a sample, such as its magnetic moment, in response to an applied magnetic field. Liquid samples can be understood as fluids containing magnetic particles, often in the form of colloidal suspensions.

[0017] It can be provided that the method comprises providing a liquid sample holder comprising a cylindrical sample space for receiving a liquid sample. This arrangement provides a well-defined, consistent geometry for holding the fluid sample, minimizing shape-related artifacts that can arise during magnetometry analysis. One advantage of this cylindrical design is its compatibility with the sample mounting systems of commercially available magnetometers.

[0018] It may also be provided that the method comprises injecting a liquid sample into the sample space of the holder through the elastomer septum. This method enables the introduction of the fluid sample without introducing air bubbles, ensuring a uniform sample distribution within the defined space.

[0019] It may also be provided that the method comprises sealing the sample space with the rigid cover. This step ensures the sample is contained within a defined volume and prevents leakage or evaporation, particularly when the sample holder is placed under vacuum or subjected to temperature changes.

[0020] It may also be provided that the method comprises mounting the sample holder in a magnetometer. This step positions the sample for analysis within the instrument’s magnetic field, enabling the measurement of its magnetic properties.

[0021] It may also be provided that the method comprises performing a magnetometry measurement of the liquid sample. This step analyzes the sample’smagnetic response to the applied magnetic field or temperature, providing information about its magnetic moment and other magnetic properties.BRIEF DESCRIPTION OF THE DRAWINGS

[0022] The following description cannot be considered limiting in any way. Various objectives, features, and advantages of the disclosed subject matter can be more fully appreciated with reference to the following detailed description of the disclosed subject matter when considered in connection with the following drawings, in which like reference numerals identify like elements.

[0023] FIG. 1 shows, according to some embodiments, (a) a liquid sample holder, machined from PCTFE, with a silicone / PTFE septum, and a magnetic fluid sample injected. It also shows (b) a schematic representation of the liquid sample holder, highlighting components and dimensions. FIG. 1 shows (c) a close-up view of the sample holder, illustrating the sample injection procedure using two needles, one for injecting the liquid sample and a second for venting air to allow complete filling.

[0024] FIG. 2 shows, according to some embodiments, the magnetic measurement results for various materials considered for use in the liquid sample holder, demonstrating their magnetic properties (e.g., diamagnetism or paramagnetism) at different temperatures (300 K and 5 K).

[0025] FIG. 3 shows, according to some embodiments, the magnetic moment and center position data (a) for an empty liquid sample holder as a function of the applied magnetic field at different temperatures (300 K and 5 K), demonstrating the holder’s background signal and thermal stability; and (b) change in center position Ad. Inset shows a close-up of the Ad data. Error bars represent 1<J.

[0026] FIG. 4 shows, according to some embodiments, (a) and the magnetic hysteresis loops and (b) center position data for a water-based magnetic fluid sample measured at 300 K using the liquid sample holder. It also shows (c) the center position data for the same sample measured at 200 K when the sample is frozen. These datademonstrate the effectiveness of the holder in minimizing artifacts caused by sample movement and shape changes.

[0027] FIG. 5 shows, according to some embodiments, a cross-section of the fluid sample holder as a shop drawing, presenting exemplary dimensions for machining the top and bottom portions of the holder, including the sample space, hollow extensions, air holes, and threaded post for attachment to a sample rod.

[0028] FIG. 6 shows, according to some embodiments, a liquid sample holder without hollow extensions.DETAILED DESCRIPTION

[0029] A detailed description of one or more embodiments is presented herein by way of exemplification and not limitation.

[0030] Conventional liquid sample holders used in magnetometry measurements often introduce significant artifacts due to the inherent mobility of fluid samples. These artifacts stem from changes in the sample’s center position, shape, and particle distribution during analysis, leading to inaccuracies in measured magnetic moments and obscuring important features of the hysteresis loop. Existing holders frequently fail to address these challenges, resulting in compromised data quality and limiting the ability to accurately characterize magnetic fluids.

[0031] The liquid sample holder 201 for magnetometry measurements described herein overcomes these limitations by providing a specialized design that minimizes sample movement, maintains a consistent geometry, and reduces spurious magnetic signals. It has been discovered that the liquid sample holder 201 for magnetometry measurements can significantly improve the accuracy and reliability of magnetic measurements of fluid samples. One advantage of this specialized holder is its ability to accommodate a wide range of fluid types and viscosities while ensuring compatibility with commercial magnetometers. The cylindrical design of the sample space, by providing a well-defined geometry, reduces shape-related distortions in the magnetic field, leading to more accurate moment measurements. The hollowextensions at each end of the sample space, by minimizing abrupt changes in the holder’s internal dimensions, further reduce spurious magnetic signals that can arise from the holder boundaries as it passes through the detection coils of the magnetometer. Another advantage of this design is its ability to accommodate complete filling of the sample space due to the elastomer septum, while maintaining structural integrity and preventing leakage through the use of a rigid cover. This arrangement enables precise and consistent sample positioning within the magnetometer, even during temperature changes or under vacuum conditions, leading to improved measurement accuracy.

[0032] In an embodiment, a liquid sample holder 201 for magnetometry measurements comprises a cylindrical sample space 200 for receiving a liquid sample, the sample space 200 having a first end 202 and a second end 204; a hollow extension 206 extending from the first end 202 of the sample space 200, the hollow extension 206 having an internal diameter substantially equal to an internal diameter of the sample space 200; a hollow extension 208 extending from the second end 204 of the sample space 200, the hollow extension 208 having an internal diameter substantially equal to the internal diameter of the sample space 200; an elastomer septum 210 sealing the sample space 200; and a cylindrical recess 224 sealing the elastomer septum 210. In an embodiment, the sample space 200 has an inner diameter, e.g., from 2.00 mm to 4.00 mm. In an embodiment, the sample space 200 has a height from 3.00 mm to 5.00 mm. In an embodiment, the sample space 200, the hollow extension 206, and the hollow extension 208 are formed as a unitary structure. In an embodiment, the elastomer septum 210 comprises a material selected from the group consisting of silicone / PTFE and a carbon black-filled perfluoroelastomer (FFKM). In an embodiment, the cylindrical recess 224 is sealed with epoxy. In an embodiment, the liquid sample holder 201 further comprises an attachment point 214 for attaching the holder to a sample rod of a magnetometer. In an embodiment, the attachment point 214 comprises a threaded post for threaded engagement with the sample rod. In an embodiment, the liquid sample holder 201 comprises polychlorotrifluoroethylene (PCTFE). In an embodiment, the liquid sample holder 201 further comprises air holes 216 (e.g., two air holes, although not limited to two) formed in the top portion of the sample holder, the air holes 216 adapted to allow release of air during sealing of the sample.

[0033] The liquid sample holder 201 for magnetometry measurements achieves performance enhancements by incorporating a number of design features aimed specifically at addressing the challenges of analyzing fluid samples. The liquid sample holder 201 comprises a cylindrical sample space 200 that defines the volume occupied by the fluid sample. This cylindrical geometry provides a well-defined shape, minimizing artifacts caused by variations in the sample’s shape and ensuring compatibility with the sample mounting systems of commercial magnetometers. This sample space 200 has a first end 202 and a second end 204, which serve to delineate the boundaries of the sample volume, contributing to precise and consistent positioning within the magnetometer. Extending from the first end 202 of the sample space 200 can be a hollow extension 206. This extension, by maintaining a consistent internal diameter with the sample space 200, minimizes spurious magnetic signals known as end effects that can arise from the edges of the sample holder as it moves through the detection coils of the magnetometer. Similarly, extending from the second end 204 of the sample space 200 can be a hollow extension 208, which mirrors the design of the first extension and further reduces end effects. Both extensions can be fabricated as hollow structures to minimize the holder’s overall thermal mass, facilitating faster temperature stabilization and enabling more accurate temperature control during analysis. The sample space 200 is sealed by an elastomer septum 210, a flexible material that allows complete filling of the space with the liquid sample without trapping air bubbles. The elastomer septum 210 can be fabricated from a variety of materials, including silicone / PTFE or carbon black-filled perfluoroelastomer (FFKM), depending on the specific requirements of the sample and solvent compatibility. A cylindrical recess 224 seals the elastomer septum 210, providing structural integrity to the holder, particularly during temperature changes or when the sample is under vacuum. This cylindrical recess 224 can be attached using epoxy or other suitable materials that provide a secure seal and maintain the holder’s shape.

[0034] The particular implementation of each element in the liquid sample holder 201 contributes to a number of technical advantages. The cylindrical sample space 200, with its clearly defined ends, ensures consistent sample positioning and minimizes shape-related artifacts. The hollow extensions, by reducing end effects and thermal mass, contribute to improved measurement accuracy and faster temperature stabilization. The elastomer septum enables complete sample filling without trappingair bubbles and allows for the preparation of air-sensitive samples, while the rigid cover provides structural integrity and ensures a consistent sample geometry. These features, taken together, significantly improve the accuracy, reliability, and versatility of magnetometry measurements of fluid samples.

[0035] To refine the performance and versatility of the liquid sample holder 201 , a number of additional features can be incorporated. The sample space 200 can have has an inner diameter from 2.00 mm to 4.00 mm, a size range that balances the need for a sufficient sample volume to provide a strong signal while minimizing shape- related artifacts that can arise with larger samples. The sample space 200 can have a height from 3.00 mm to 5.00 mm, further optimizing the sample volume for compatibility with commercial magnetometers and reducing the potential for significant measurement errors. In some embodiments, the sample space 200, the hollow extension 206, and the hollow extension 208 are formed as a unitary structure during the machining process, simplifying construction and ensuring a consistent internal diameter throughout the holder. The elastomer septum 210 may comprise a material such as silicone / PTFE, a carbon black-filled perfluoroelastomer (FFKM), and the like, depending on the solvent compatibility requirements of the sample and the desired temperature range for analysis. The cylindrical recess 224, which provides a secure seal over the elastomer septum 210, can be attached using epoxy, offering good adhesion and structural integrity while being compatible with a wide range of solvents. To facilitate mounting in a magnetometer, the liquid sample holder 201 may also include an attachment point 214. This attachment point 214 can be implemented as a threaded post 232, allowing for secure attachment to the sample rod of the magnetometer. The main body of the liquid sample holder 201 can be fabricated, e.g., from polychlorotrifluoroethylene (PCTFE) or another material known for its low magnetic susceptibility, good chemical resistance, and ability to withstand a wide range of temperatures. To ensure removal of air from the sample space 200 during the sealing process, air holes 216 are formed in the top portion of the holder. These air holes 216 allow for the escape of any trapped air as the epoxy or adhesive used for sealing cures, minimizing the potential for air bubbles to distort the magnetic field and affect measurements.

[0036] These additional features contribute to the technical advantages of the liquid sample holder 201 by optimizing sample volume, simplifying construction, expanding solvent compatibility, ensuring secure mounting, and facilitating air removal during sealing. The use of PCTFE as the holder material minimizes background magnetic signals, while the precise dimensions of the sample space ensure compatibility with commercial magnetometers. The choice of materials for the elastomer septum and cylindrical recess 224, coupled with the inclusion of air holes, enables complete sample filling, prevents particle immobilization, and minimizes the risk of air bubbles, all contributing to accurate and reliable magnetometry measurements.

[0037] At the core of the liquid sample holder 201 is the cylindrical sample space 200, a precisely dimensioned cavity that houses the fluid sample during magnetometry measurements. This sample space 200 is machined into both the top and bottom portions of the holder, forming a continuous cylindrical volume when the two portions are joined. The precise dimensions of this sample space 200, typically with an inner diameter from 1 mm to 12.7 mm, specifically from 2 mm to 4 mm, and a height from 3.00 mm to 5.00 mm, are chosen to balance a sufficient sample volume to generate a strong signal while minimizing shape-related distortions of the magnetic field that can lead to measurement artifacts. The sample space 200 can be interconnected with two hollow extensions, one extending from each end, which serve to maintain a consistent internal diameter throughout the length of the holder. This arrangement minimizes end effects, reducing spurious magnetic signals that can arise from the holder boundaries as it moves through the detection coils of the magnetometer. The sample space 200 is sealed at one end by an elastomer septum, which allows for the complete filling of the space without trapping air bubbles and prevents particle immobilization during the sealing process. The other end of the sample space 200 is sealed by a rigid cover, typically attached using epoxy, which provides structural integrity to the holder and maintains a consistent sample geometry, particularly during temperature changes or under vacuum.

[0038] The cylindrical sample space 200 provides a number of technical advantages that contribute to the improved accuracy and reliability of magnetometry measurements. Its precisely controlled dimensions optimize sample volume,minimizing shape-related artifacts while ensuring compatibility with existing sample handling systems of commercial magnetometers. The continuous cylindrical geometry, extending through the hollow extensions, reduces end effects and spurious magnetic signals, leading to more accurate magnetic moment measurements. The ability to seal the sample space 200 with an elastomer septum allows for complete filling without trapping air bubbles and enables the preparation of air-sensitive samples, while the rigid cover ensures structural integrity and maintains a consistent sample geometry even under challenging conditions. These features, taken together, significantly enhance the performance and versatility of the liquid sample holder 201 for analyzing the magnetic properties of fluid samples.

[0039] The cylindrical sample space 200 of the liquid sample holder 201 possesses a first end 202, which represents one of the boundaries of the sample volume. This first end 202 can be defined by the machined surface of the holder material, either PCTFE or another suitable low magnetic susceptibility material. The first end 202 is interconnected with a hollow extension, which maintains a consistent internal diameter with the sample space, minimizing end effects and reducing thermal mass. It serves as a reference point for determining the sample’s center position during magnetometry measurements, ensuring accurate and consistent placement within the instrument’s sensitive region.

[0040] The presence of a first end 202 on the cylindrical sample space 200 provides a clearly defined boundary for the sample volume, contributing to the accurate determination of the sample’s center position for precise magnetometry analysis. This defined boundary, coupled with the hollow extension that minimizes end effects, enhances the accuracy and reliability of magnetic moment measurements, particularly when the sample holder is moved through the detection coils of the magnetometer.

[0041] Mirroring the first end 202, the cylindrical sample space 200 of the liquid sample holder 201 also includes a second end 204, representing the opposing boundary of the sample volume. This second end 204, typically a machined surface of PCTFE or another suitable material, is interconnected with a hollow extension that maintains a consistent internal diameter with the sample space, minimizing end effects and reducing thermal mass. It provides a reference point for determining the sample’scenter position and contributes to precise and consistent positioning during magnetometry measurements.

[0042] By providing a clearly defined boundary for the sample volume, the second end 204, in conjunction with the first end 202, enables accurate determination of the sample’s center position, which is essential for precise and consistent magnetometry measurements. The inclusion of a hollow extension on this second end 204 further reduces spurious magnetic signals and minimizes thermal mass, enhancing the accuracy and speed of temperature control during analysis.

[0043] The liquid sample holder 201 can incorporate a hollow extension 206 that extends from the first end 202 of the cylindrical sample space 200. This hollow extension 206 can be machined from the same low magnetic susceptibility material as the sample space 200, ensuring a consistent magnetic environment throughout the holder. It maintains an internal diameter substantially equal to the inner diameter of the sample space 200, creating a smooth transition in the internal dimensions and minimizing abrupt changes in the magnetic field that can lead to spurious signals. The hollow design of the extension reduces its thermal mass, allowing for faster temperature stabilization during measurements and minimizing temperature gradients that could affect the sample.

[0044] The hollow extension 206, by maintaining a consistent internal diameter with the sample space 200, reduces end effects that can distort the magnetic field and lead to inaccuracies in measured magnetic moments. Its hollow structure minimizes thermal mass, facilitating faster temperature stabilization and contributing to more accurate temperature control during analysis. This arrangement enhances the precision and reliability of magnetometry measurements while expanding the range of temperatures over which the holder can be used effectively.

[0045] Mirroring the hollow extension 206 on the first end 202, the liquid sample holder 201 can also incorporate a hollow extension 208 extending from the second end 204 of the sample space 200. This hollow extension 208 can be machined from the same material as the sample space 200 and the first extension 206, maintaining a consistent magnetic environment. It has an internal diameter substantially equal to the inner diameter of the sample space 200, contributing to asmooth transition in the holder’s internal dimensions and further minimizing end effects. The hollow design of this second extension 208 also reduces thermal mass, facilitating faster temperature stabilization during analysis.

[0046] The hollow extension 208, by providing a continuation of the sample space’s internal dimensions, minimizes end effects and enhances the accuracy of magnetic moment measurements. Its hollow structure, like that of the first extension 206, contributes to reducing the holder’s overall thermal mass, enabling faster temperature stabilization and improving the accuracy of temperature control during magnetometry analysis.

[0047] The liquid sample holder 201 incorporates an elastomer septum 210, a component that enables complete filling of the sample space 200 while preventing particle immobilization during the sealing process. The elastomer septum 210 can be a disc-shaped component, sized to fit snugly within the top portion of the holder and create a secure seal against the walls of the sample space 200. This septum 210 can be fabricated from a variety of elastomeric materials, including silicone / PTFE or a carbon black-filled perfluoroelastomer (FFKM), chosen based on their compatibility with the specific fluid sample and solvent being analyzed. It is interconnected with the sample space 200, providing a barrier against leakage or evaporation of the sample, and with the cylindrical cover 224, which provides additional sealing and structural support. The elastomer septum 210 is designed to self-seal after sample injection, minimizing the risk of contamination and facilitating the preparation of air-sensitive samples.

[0048] The elastomer septum 210 contributes to the technical advantages of the liquid sample holder 201 by providing a reliable seal for the sample space 200 while allowing for complete filling without trapping air bubbles. Its self-sealing properties minimize the risk of contamination and enable the preparation of airsensitive samples. The flexibility of the elastomer septum 210 ensures a tight seal even if the sample volume changes slightly due to temperature variations, while its compatibility with a range of materials expands the versatility of the holder for analyzing diverse fluid samples.

[0049] To facilitate secure and precise positioning within a magnetometer, the liquid sample holder 201 can include an attachment point 214. This attachment point 214 can be located on the top portion of the holder 220 and is designed to interface with the sample rod of the magnetometer. It can be implemented in various forms, including a threaded post 232 that allows for threaded engagement with the sample rod, ensuring a secure and stable connection. The attachment point 214 is interconnected with the main body of the holder, providing a mechanically robust link for supporting the holder and sample during measurements.

[0050] The inclusion of an attachment point 214 provides an interface for securely mounting the liquid sample holder 201 within the magnetometer. This arrangement ensures precise and consistent positioning of the sample, minimizing positional errors that can lead to inaccuracies in measurements. The robust mechanical connection between the attachment point 214 and the holder body provides stability during analysis, particularly when the sample is moved or subjected to temperature changes.

[0051] The liquid sample holder 201 includes air holes 216, small openings positioned in the top portion of the holder to facilitate air removal during the attachment process for the rigid cover. These air holes 216 can be located near the edge of the holder, allowing for the efficient escape of trapped air as the epoxy or adhesive used for sealing cures. They are interconnected with the sample space 200, providing a pathway for air to be vented from the internal volume. The size and placement of these air holes 216 are designed to allow for the removal of air while preventing leakage of the liquid sample during or after sealing.

[0052] The presence of air holes 216 enables complete sealing of the sample space 200 without trapping air bubbles that can distort the magnetic field and affect measurement accuracy. This arrangement ensures a uniform and consistent sample environment, contributing to the reliability and precision of magnetometry measurements.

[0053] The liquid sample holder 201 can be constructed from two a top portion 220 and a bottom portion 222. These portions can be machined separately, e.g., from PCTFE or another suitable low-magnetic susceptibility material, then joinedto form the complete holder. The top portion 220 includes a cylindrical recess 224, It also typically contains the air holes 216 that facilitate air removal during the sealing process. The top portion 220 is interconnected with the bottom portion 222, forming the complete sample space 200 when joined. The top portion 220 typically also incorporates the attachment point 214, such as a threaded post 232, for securing the holder to the sample rod of the magnetometer.

[0054] The separate machining of the top portion 220 enables precise control over the dimensions and features of the cylindrical recess 224, optimizing the sample volume and ensuring a secure fit over the elastomer septum 210. The inclusion of air holes 216 in the top portion 220 facilitates air removal during sealing, minimizing the potential for air bubbles within the sample space 200. The inclusion of the attachment point 214 on the top portion 220 facilitates secure and stable mounting within the magnetometer, minimizing positional errors that could affect measurement accuracy. This arrangement contributes to a more robust and versatile holder design, adaptable to a wider range of sample types and experimental conditions.

[0055] Complementing the top portion 220, the liquid sample holder 201 also includes a bottom portion 222, machined from a low magnetic susceptibility material. This bottom portion 222 includes a cylindrical cavity 226, which, when aligned and joined with the cylindrical recess 224 of the top portion 220, forms the complete sample space 200 for receiving the liquid sample.

[0056] The separate machining of the bottom portion 222 enables precise control over the dimensions and features of the cylindrical cavity 226, ensuring proper alignment with the recess in the top portion to form a continuous, well-defined sample space 200.

[0057] The top portion 220 of the liquid sample holder 201 includes a cylindrical recess 224, a precisely machined cavity designed to create a rigid cover to seal the elastomer septum 210, providing additional security and structural support to the sample holder. This recess 224 can be formed using a lathe or other precision machining techniques, ensuring a smooth, cylindrical surface that minimizes shape- related distortions of the magnetic field. Its dimensions are carefully controlled to align precisely with the cylindrical cavity 226 in the bottom portion 222, creating acontinuous, well-defined sample space 200 when the two portions are joined. The cylindrical recess 224 is interconnected with the elastomer septum 210, providing a primary seal for the sample space 200, and with the air holes 216, allowing for the escape of trapped air during sealing.

[0058] The cylindrical recess 224 can be attached with a conformal material such as a layer of epoxy, applied over the elastomer septum 210 and the surrounding surface of the holder. The sealed cylindrical recess forms a hard, durable seal that prevents leakage or evaporation of the sample, even under vacuum or during temperature changes.

[0059] The precise machining of the cylindrical recess 224 contributes to the accuracy and reliability of magnetometry measurements by minimizing shape-related artifacts and ensuring a secure fit for the elastomer septum 210. The alignment of this recess 224 with the cavity in the bottom portion creates a continuous sample space 200, further reducing end effects and enabling more accurate magnetic moment measurements.

[0060] The cylindrical recess 224 adds to the holder’s structural integrity, ensuring the sample space 200 maintains a consistent geometry during magnetometry measurements. It prevents deformation or leakage of the fluid sample, particularly under vacuum conditions or during thermal cycling. This arrangement contributes to more accurate and reliable measurements, expanding the range of conditions under which the holder can be used effectively.

[0061] The bottom portion 222 of the liquid sample holder 201 includes a cylindrical cavity 226, a machined space that, when aligned and joined with the cylindrical recess 224 in the top portion 220, forms the complete sample space 200. The cylindrical cavity 226 can be machined using the same precision techniques as the recess 224, ensuring a smooth surface and accurate dimensions. Its design complements the recess in the top portion 220, creating a continuous, well-defined volume for containing the liquid sample during magnetometry measurements.

[0062] The cylindrical cavity 226, by precisely matching the dimensions of the cylindrical recess 224 in the top portion 220, ensures a continuous and well- defined sample space 200, minimizing end effects and contributing to the accuratemeasurement of the sample’s magnetic properties. This arrangement allows for consistent positioning of the sample within the magnetometer, further reducing positional errors that could affect the accuracy of the analysis.

[0063] To ensure a secure and reliable seal between the elastomer septum 210 and the sample space 200, the bottom portion 222 of the liquid sample holder 201 may incorporate a shelf 230. This shelf 230 can be a machined ring or ledge that provides a seating surface for the elastomer septum 210, ensuring proper alignment and preventing displacement during the sealing process. The elastomer septum 210 is secured to this shelf 230 using a suitable adhesive, chosen for its compatibility with both the elastomer material and the PCTFE of the holder body.

[0064] The incorporation of a shelf 230 within the top portion 220 provides a dedicated seating surface for the elastomer septum 210, ensuring proper alignment and a secure seal for the sample space 200. This arrangement reduces the risk of leakage or contamination and enhances the structural integrity of the holder, particularly during handling and transportation.

[0065] The liquid sample holder 201 incorporates a threaded post 232, a feature machined into the bottom portion 222, to provide a secure and precise means of attaching the holder to the sample rod of a magnetometer. This threaded post 232 can be designed to match the threading specifications of standard sample rods used in commercial magnetometers. It enables straightforward and reliable mounting of the holder, minimizing positional errors that can lead to inaccuracies in measurements.

[0066] The threaded post 232 ensures secure and precise attachment of the liquid sample holder 201 to the magnetometer’s sample rod, enabling accurate and reproducible positioning of the sample within the instrument’s sensitive region. This arrangement contributes to the overall robustness and reliability of the holder design, simplifying sample handling and facilitating precise measurements.

[0067] In an embodiment, with reference to FIG. 1 , the liquid sample holder 201 can be machined from PCTFE, as shown, with a cylindrical form and the presence of a silicone / PTFE septum. A dark region within the holder indicates the presence of a magnetic fluid sample that has been injected into the sample space. A schematic diagram of the holder further clarifies its design, showing a cylindrical sample space,hollow extensions on both ends, an elastomer septum, and a screw mechanism for attachment to a sample rod. The outer diameter of the holder can be around 6 mm, while the inner diameter of the sample space is approximately 3.45 mm. The hollow extensions, both at the top and bottom, maintain the same inner diameter as the sample space, ensuring a smooth transition in dimensions and minimizing end effects. Two small air holes are also depicted near the top of the holder, serving as vents for air removal during the sealing process.

[0068] A close-up view of the sample holder illustrates the sample injection procedure, including an elastomer septum for sealing. The injection process involves two needles, one for introducing the liquid sample into the sample space and a second for venting air, allowing for complete filling and preventing the formation of air bubbles. The first needle, connected to a syringe, is inserted through the elastomer septum, while the second needle provides a vent for air to escape. After the sample space is filled, the needles are removed, and the elastomer septum self-seals, minimizing the risk of contamination. The top portion of the holder is then secured, typically using epoxy, to provide a rigid cover over the septum and ensure structural integrity. This arrangement allows for the secure containment of the liquid sample, preventing leakage or evaporation, and ensures that the sample maintains a consistent geometry during analysis, particularly when subjected to temperature changes or placed under vacuum.

[0069] FIG. 1 , by visually depicting the liquid sample holder 201 and its key features, provides a design and functionality. The cylindrical sample space, hollow extensions, elastomer septum, air holes, and threaded attachment point are illustrated. The detailed dimensions shown in FIG. 5 and close-up view of the sample injection procedure provide those skilled in the art to implement and use the liquid sample holder 201 effectively for magnetometry measurements of fluid samples.

[0070] FIG. 5 shows a detailed shop drawing of the liquid sample holder 201 , providing exemplary dimensions and specifications for its fabrication, enabling skilled machinists to construct the holder with precision. The drawing depicts a crosssection of the holder, including the dimensions for the sample space, hollow extensions, air holes, and threaded attachment point. The overall height of the holder is approximately 30 mm, with the sample space occupying a central portion of thatheight. The inner diameter of the sample space is shown to be 3.4 mm, while its height is 4.0 mm. The hollow extensions, both at the top and bottom, maintain the same inner diameter as the sample space, extending for a distance of approximately 3.8 mm each.

[0071] Two air holes, with a diameter of 1.2 mm, are depicted near the bottom of the top portion of the holder, providing vents for air removal during the sealing process. A threaded post, with 8-32 screw threads, is shown extending from the top of the holder, providing a means for attaching the holder to the sample rod of a magnetometer. The drawing also includes detailed dimensions for the thickness of the holder walls, the diameter of the outer body, and the placement of the shelf that supports the elastomer septum. It is important to note that the dimensions presented in FIG. 5 are exemplary and provided for illustrative purposes. Skilled artisans will recognize that a range of dimensions can be used to fabricate the liquid sample holder 201 , depending on the specific requirements of the application, such as the type of magnetometer being used, the volume of the fluid sample, and the desired temperature range for analysis.

[0072] The shop drawing presented in FIG. 5, by providing detailed dimensions and specifications, enables the precise fabrication of the liquid sample holder 201 , ensuring the accurate and consistent positioning of fluid samples during magnetometry measurements. The drawing guides the machining process, allowing for the creation of a cylindrical sample space with smooth walls and well-defined ends, minimizing shape-related artifacts. The inclusion of hollow extensions, air holes, and a threaded attachment point further enhances the functionality and versatility of the holder that can be specific to the magnetometer and its mounting configuration. The specific dimensions provided in the drawing, while exemplary, serve as a starting point for skilled machinists, allowing for adjustments based on the specific requirements of the application while maintaining the core design principles of the liquid sample holder 201.

[0073] In an embodiment, with reference to FIG. 6, the liquid sample holder 201 can include a top portion 220 that comprises: a cylindrical recess 224 inside of a first end 202 with air holes 216; a bottom portion 222 disposed on the top portion 220 and that comprises: a second end 204, a cylindrical cavity 226, and a shelf 230 that receives an elastomer septum 210, wherein hollow extensions are absent. In someembodiments, a single hollow extension can extend from the top portion 220 or from the bottom portion 222.

[0074] Liquid sample holder 201 can be made of various elements and components that are fabricated. Elements of liquid sample holder 201 can be various sizes. Lenghts of various components of liquid sample holder 201 independendently can be from 1 millimeter (mm) to 51 millimeter (mm), and specifically from 3 mm to 5 mm. Further, diameters or largest internal dimensions of components of components of liquid sample holder 201 independendently can be from 1 millimeter (mm) to 12.7 mm, and specifically from 2 mm to 4 mm.

[0075] While the exemplary dimensions provided for the sample space 200 and hollow extensions 206 and 208 have been shown to be effective for a range of magnetometry measurements, it is understood that these dimensions can be varied to suit specific applications and instrument requirements. The inner diameter of the sample space 200 can be adjusted to accommodate different sample volumes, balancing the need for a strong signal with the minimization of shape-related artifacts. Similarly, the height of the sample space 200 and the length of the hollow extensions 206 and 208 can be tailored to match the geometry and sensitivity of the magnetometer’s detection coils, ensuring optimal signal capture and reducing end effects. The dimensions of the air holes 216 can also be adjusted to balance the need for efficient air removal during sealing with the prevention of sample leakage. These variations in size and dimensions allow for the customization of the liquid sample holder 201 to meet the specific requirements of various magnetometry applications and instruments, ensuring optimal performance and measurement accuracy.

[0076] Elements of liquid sample holder 201 can be made of a material that is physically or chemically resilient in an environment in which liquid sample holder 201 is disposed. Exemplary materials include a plastic, ceramic, thermoplastic, glass, semiconductor, and the like. The elements of liquid sample holder 201 can be made of the same or different material and can be monolithic in a single physical body or can be separate members that are phsycially joined.

[0077] While PCTFE has been identified as a material for constructing the liquid sample holder 201 , other materials possessing suitable properties may also beemployed. The materials for the holder material have low magnetic susceptibility, good chemical resistance, and compatibility with the target fluid samples and solvents. Alternative polymeric materials that can be considered include polycarbonate, acrylic, and polyvinyl chloride (PVC), each offering varying degrees of chemical resistance and mechanical strength. For applications requiring higher temperature resistance or improved structural integrity, materials such as polyetheretherketone (PEEK) or polyetherimide (PEI) can be considered. For specialized applications involving corrosive solvents or extreme temperatures, materials like quartz glass can be employed. The selection of the most appropriate material for the liquid sample holder 201 will depend on the specific requirements of the magnetometry measurements, including the type of fluid being analyzed, the desired temperature range, and the presence of any potentially reactive or corrosive components.

[0078] While a cylindrical sample space 200 has been described for the liquid sample holder 201 , other geometric shapes can be employed to accommodate different sample volumes, minimize shape-related artifacts, or enhance compatibility with specific magnetometer designs. Spherical or ellipsoidal sample spaces can provide a more uniform magnetic field environment, reducing distortions and improving measurement accuracy. Rectangular or square sample spaces can be used for specific applications where a larger surface area is desired for interaction with the magnetic field. These alternative shapes, while departing from the cylindrical design, still incorporate the key features of the liquid sample holder 201 , such as hollow extensions, an elastomer septum, and a rigid cover, to minimize end effects, enable complete sample filling, and maintain structural integrity. The choice of the most suitable shape for the sample space will be guided by the specific requirements of the magnetometry measurements, balancing the need for accurate measurements with compatibility with the chosen instrument and sample properties.

[0079] Liquid sample holder 201 can be made in various ways. It should be appreciated that liquid sample holder 201 includes a number of mechanical components, wherein such components can be interconnected and placed in communication (e.g., fluid communication, mechanical communication, and the like) by physical, chemical, optical, or other interconnects. Elements of liquid sample holder 201 can be formed from silicon, silicon nitride, and the like although other suitablematerials, such plastic, ceramic, or glass can be used. According to an embodiment, the elements of liquid sample holder 201 are formed using 3D printing although the elements of liquid sample holder 201 can be formed using other methods, such as injection molding or machining a stock material such as block of material that is subjected to removal of material such as by cutting, laser oblation, and the like. Accordingly, liquid sample holder 201 can be made by additive or subtractive manufacturing. In an embodiment, elements of liquid sample holder 201 are selectively etched to remove various different materials using different etchants and photolithographic masks and procedures. The various layers thus formed can be subjected to joining by bonding to form liquid sample holder 201 .

[0080] In an embodiment, a process for fabricating a liquid sample holder 201 for magnetometry measurements comprises machining a top portion 220 and a bottom portion 222 of the holder from polychlorotrifluoroethylene (PCTFE) or other suitable material, the top portion 220 comprising a cylindrical recess 224 sized to receive a liquid sample and the bottom portion 222 comprising a cylindrical cavity 226 sized to receive the liquid sample, wherein the cylindrical recess 224 and cylindrical cavity 226 form a sample space 200 for receiving the liquid sample when the top portion 220 and bottom portion 222 are joined; inserting an elastomer septum 210 into the bottom portion 222, the elastomer septum 210 sized to seal the cylindrical recess 224 resting on shelf 230; and joining the top portion 220 and the bottom portion 222 such that the cylindrical recess 224 and the cylindrical cavity 226 are aligned to form the sample space 200. In an embodiment, the machining comprises forming a hollow extension 206 extending from a first end 202 of the cylindrical recess 224, the hollow extension 206 having an internal diameter substantially equal to an inner diameter of the cylindrical recess 224; and forming a hollow extension 208 extending from a second end 204 of the cylindrical cavity 226, the hollow extension 208 having an internal diameter substantially equal to the inner diameter of the cylindrical cavity 226. In an embodiment, the machining further comprises forming air holes 216 in the top portion 220, the air holes 216 adapted to allow release of air from the sample space 200 during sealing. In an embodiment, the inserting the elastomer septum 210 comprises securing the elastomer septum 210 to a shelf 230 in the bottom portion 222 with adhesive. In an embodiment, the joining comprises securing the top portion 220 and the bottom portion 222 together with adhesive. In an embodiment, the processfurther comprises applying epoxy over the elastomer septum 210 after joining the top portion 220 and bottom portion 222. In an embodiment, the machining further comprises forming a threaded post 232 in the top portion 220, the threaded post 232 adapted to threadably engage a sample rod of a magnetometer. In an embodiment, the cylindrical recess 224 has an inner diameter from 2 mm to 4 mm. In an embodiment, the cylindrical cavity 226 has a height from 3 mm to 5 mm. In an embodiment, the elastomer septum 210 comprises a material that includes silicone / PTFE, carbon black-filled perfluoroelastomer (FFKM), and the like.

[0081] The process for fabricating the liquid sample holder 201 enables the precise and reproducible construction of this specialized device. The process can start with machining a top portion 220 and a bottom portion 222 of the holder from a suitable material such as polychlorotrifluoroethylene (PCTFE), a material chosen for its low magnetic susceptibility, good chemical resistance, and compatibility with a wide range of solvents. These portions can be machined separately, using a lathe or other precision machining techniques, to create the desired shapes and dimensions. The top portion 220 includes a cylindrical recess 224, sized to receive the liquid sample, while the bottom portion 222 comprises a cylindrical cavity 226, also sized to receive the liquid sample. These two cavities, when aligned and joined, form the complete sample space 200 for containing the liquid sample during magnetometry measurements. An elastomer septum 210, made from a material such as silicone / PTFE or FFKM, is then inserted into the bottom portion 222. This elastomer septum 210 is sized to seal the cylindrical recess 226 by sealing with shelf 230 and create a barrier against leakage or evaporation of the sample. The final step in the fabrication process involves joining the top portion 220 and the bottom portion 222, ensuring that the cylindrical recess 224 and the cylindrical cavity 226 are precisely aligned to form the complete sample space 200.

[0082] The process for fabricating the liquid sample holder 201 enables the precise construction of a device optimized for magnetometry measurements of fluid samples. The use of PCTFE as the holder material minimizes background magnetic signals, while the separate machining of the top and bottom portions, with their precisely dimensioned recesses and cavities, ensures a continuous and well-defined sample space, reducing end effects and contributing to accurate momentmeasurements. The insertion of an elastomer septum provides a reliable seal, allowing for complete filling of the sample space without trapping air bubbles and accommodating air-sensitive samples. These features, taken together, enable the reproducible fabrication of a liquid sample holder 201 that addresses the challenges of analyzing fluid samples and enables accurate and reliable characterization of their magnetic properties.

[0083] The fabrication process for the liquid sample holder 201 can be further refined with several additional steps and features, contributing to its functionality and versatility. During the machining of the top portion 220 and bottom portion 222, hollow extensions 206 and 208 can be formed, extending from the first end 202 of the cylindrical recess 224 and the second end 204 of the cylindrical cavity 226, respectively. These extensions are designed to maintain an internal diameter substantially equal to the inner diameter of the sample space 200, ensuring a smooth transition in dimensions and minimizing end effects. Air holes 216, e.g., with a diameter of around 1 mm, are also formed in the top portion 220 during machining. These air holes 216 act as vents for the removal of trapped air from the sample space 200 during the sealing process, preventing the formation of air bubbles that could distort the magnetic field and affect measurements. The elastomer septum 210, which seals the cylindrical recess 226 in the bottom portion 222, can be secured using adhesive to shelf 230, creating a reliable seal and preventing displacement during the subsequent sealing of the sample space 200. This adhesive can be applied to a shelf 230, a machined ring or ledge within the bottom portion 222 that provides a dedicated seating surface for the elastomer septum 210. The top and bottom portions 220 and 222 can be joined using adhesive, such as a layer of epoxy which is also applied over the elastomer septum 210, providing a seal and additional structural support. During the machining process, a threaded post 232 can be formed in the top portion 220, providing a means for securely attaching the holder to a sample rod of a magnetometer. The inner diameter of the cylindrical recess 224 and cylindrical cavity 226 can be, e.g., from 2 mm to 4 mm, while the height of the cavity 226 can be from 3 mm to 5 mm. These dimensions optimize the sample volume, balancing signal strength with minimal shape-related artifacts and ensuring compatibility with existing sample handling systems. The choice of material for the elastomer septum 210 can be tailored to the specific application, with silicone / PTFE and carbon black-filledperfluoroelastomer (FFKM) offering excellent sealing properties and compatibility with a range of solvents and temperatures.

[0084] These additional features and variations in the fabrication process contribute to the technical advantages of the liquid sample holder 201 by optimizing its performance, versatility, and ease of use. The hollow extensions on both the top and bottom portions of the holder reduce end effects and minimize thermal mass, while the air holes facilitate complete air removal during sealing, ensuring a bubble-free sample environment. The use of adhesive to secure the elastomer septum and join the holder portions simplifies construction, while the application of epoxy provides additional sealing and structural support. The inclusion of a threaded post enables secure and precise attachment to a magnetometer’s sample rod, while the precisely controlled dimensions of the sample space optimize sample volume and ensure compatibility with commercial instruments. The choice of elastomer materials allows for compatibility with a wider range of solvents and temperatures, expanding the versatility of the liquid sample holder 201 for analyzing diverse magnetic fluids.

[0085] The process of fabricating the liquid sample holder 201 can begin with machining a top portion 220 and a bottom portion 222 of the holder from a suitable material, such as PCTFE. This machining step involves using precision techniques, including lathing, milling, and drilling, to create the desired shapes and dimensions of the holder components. The top portion 220 is machined to include a cylindrical recess 224,. This recess 224 is carefully machined to ensure a smooth and precise cylindrical surface, minimizing distortions in the magnetic field that could affect measurements. The bottom portion 222 is machined to include a cylindrical cavity 226, sized to receive the liquid sample and house the elastomer septum. Cylindrical recess 226, when aligned and joined with the cylindrical recess 224 of the top portion 220, forms the complete sample space for the liquid sample. The machining process for both portions also includes the formation of hollow extensions on the ends of the sample space, maintaining a consistent internal diameter and reducing end effects. Air holes are drilled into the top portion 220 to facilitate the removal of trapped air during the sealing process, ensuring a bubble-free sample environment. The top portion 220 is machined to incorporate a threaded post 232, enabling secure attachment to the sample rod of the magnetometer. The precise dimensions of the cylindrical recess 224, cylindricalcavity 226, and hollow extensions are carefully controlled during machining to ensure compatibility with the chosen magnetometer and optimize the sample volume for accurate measurements.

[0086] After the top portion 220 and bottom portion 222 are machined, an elastomer septum 210 is carefully inserted into the bottom portion 222. The septum 210, typically made from a material like silicone / PTFE or FFKM, is sized to precisely fit within the cylindrical recess 226 of the bottom portion 222. It is positioned on a machined shelf 230, a ring-like structure within the recess 226, ensuring proper alignment and a secure seal. A suitable adhesive is then applied to the shelf 230, securing the elastomer septum 210 in place and preventing displacement during subsequent steps in the fabrication process. This adhesive is chosen for its compatibility with both the elastomer material and the PCTFE holder body, ensuring a strong and durable bond. The insertion of the elastomer septum 210 creates a primary seal for the sample space, allowing for the introduction of the liquid sample without trapping air bubbles. The self-sealing properties of the elastomer material ensure that the septum 210 closes tightly after the injection needle is withdrawn, minimizing the risk of contamination and facilitating the preparation of air-sensitive samples.

[0087] Fabricating the liquid sample holder 201 involves joining the top portion 220 and the bottom portion 222, ensuring that the cylindrical recess 224 and the cylindrical cavity 226 are precisely aligned to create the complete sample space 200. This joining process can be accomplished using a suitable adhesive, chosen for its strength, durability, and compatibility with PCTFE. The adhesive is applied to the mating surfaces of the top and bottom portions 220 and 222, and the two portions are carefully aligned, ensuring that the cylindrical recess 224 and cavity 226 form a continuous, uninterrupted cylindrical volume. After the adhesive is applied, the two portions are held together under pressure until the adhesive cures, creating a strong bond that ensures the structural integrity of the holder. This joining process results in a fully sealed sample space 200, ready to be mounted within a magnetometer for analysis.

[0088] In an embodiment, a method of performing magnetometry measurements of a liquid sample comprises providing a liquid sample holder 201 comprising a cylindrical sample space 200 for receiving a liquid sample, the samplespace 200 having a first end 202 and a second end 204; a hollow extension 206 extending from the first end 202 of the sample space 200, the hollow extension 206 having an internal diameter substantially equal to an internal diameter of the sample space 200; a hollow extension 208 extending from the second end 204 of the sample space 200, the hollow extension 208 having an internal diameter substantially equal to the internal diameter of the sample space 200; an elastomer septum 210 sealing the sample space 200; and a cylindrical recess 224 sealing the elastomer septum 210; injecting a liquid sample into the sample space 200 of the holder through the elastomer septum 210; sealing the sample space 200 with the cylindrical recess 224; mounting the sample holder in a magnetometer; and performing a magnetometry measurement of the liquid sample. In an embodiment, the injecting comprises injecting the liquid sample with a first syringe and a first needle inserted through the elastomer septum 210; and venting air from the sample space 200 with a second needle inserted through the elastomer septum 210. In an embodiment, the sealing the sample space 200 comprises applying epoxy over the elastomer septum 210 before covering the cylindrical recess 226 with the cylindrical recess 224. In an embodiment, the mounting the sample holder in a magnetometer comprises threading the sample holder onto a sample rod of the magnetometer. In an embodiment, the performing a magnetometry measurement comprises measuring a magnetic moment of the liquid sample in response to an applied magnetic field. In an embodiment, the method further comprises determining a center position of the liquid sample during the measurement. In an embodiment, the method further comprises adjusting a position of the sample holder to a determined center position of the liquid sample. In an embodiment, the performing a magnetometry measurement comprises performing a measurement at a temperature from 5 K to 300 K. In an embodiment, the performing a magnetometry measurement comprises performing the measurement at a temperature where the liquid sample is frozen. In an embodiment, the magnetometer comprises an instrument such as a vibrating sample magnetometer, a superconducting quantum interference device magnetometer, an alternating gradient magnetometer, and the like.

[0089] Various embodiments provide a method of performing magnetometry measurements of a liquid sample that addresses the aforementioned challenges associated with analyzing fluid materials. The method involves a series of steps, beginning with providing a liquid sample holder 201 specifically designed to minimizeartifacts and ensure accurate measurements. This holder comprises a cylindrical sample space 200, which serves as a well-defined container for the liquid sample, minimizing shape-related distortions of the magnetic field. The cylindrical sample space 200 has a first end 202 and a second end 204, delineating the boundaries of the sample volume and contributing to the accurate positioning of the sample within the magnetometer. Extending from each end of the sample space 200 are hollow extensions, 206 and 208, designed to minimize spurious magnetic signals known as end effects that can arise from the holder’s boundaries as it moves through the detection coils of the instrument. These hollow extensions maintain an internal diameter substantially equal to the inner diameter of the sample space 200, ensuring a smooth transition in dimensions and further reducing end effects. An elastomer septum 210 seals the sample space 200, allowing for complete filling without trapping air bubbles and preventing particle immobilization during the sealing process. This elastomer septum 210 can be made from a material such as silicone / PTFE or FFKM, chosen for its compatibility with the specific fluid sample and solvent being analyzed. The elastomer septum 210 is then covered with a cylindrical recess 224, often sealed using epoxy, which provides structural integrity to the holder and maintains a consistent sample geometry during analysis. The method then involves injecting a liquid sample into the sample space 200 of the holder through the elastomer septum 210, enabling the introduction of the fluid without introducing air bubbles and ensuring a uniform sample distribution. The sample space 200 is then sealed with the rigid cover 212, securing the sample within a defined volume and preventing leakage or evaporation. The sample holder is then mounted in a magnetometer, e.g., by threading it onto a sample rod, allowing for precise and consistent positioning within the instrument’s magnetic field. Finally, the method involves performing a magnetometry measurement of the liquid sample, analyzing its magnetic response to the applied field to determine its magnetic moment and other properties.

[0090] The steps in the method of performing magnetometry measurements of a liquid sample contributes to the overall accuracy and reliability of the analysis. The use of a specialized liquid sample holder 201 , with its cylindrical sample space, hollow extensions, elastomer septum, and rigid cover minimizes sample movement, maintains a consistent geometry, and reduces spurious magnetic signals, enabling accurate and reproducible measurements. The injection of the sample through theelastomer septum prevents the formation of air bubbles, ensuring a uniform sample distribution within the defined volume. The secure mounting of the holder within the magnetometer, coupled with the subsequent measurement of the sample’s magnetic response, provides a comprehensive and reliable method for characterizing the magnetic properties of fluid materials.

[0091] The method of performing magnetometry measurements of a liquid sample can be further refined with several optional steps. The process of injecting the liquid sample into the sample space 200 of the holder can be accomplished using a two-needle technique. This technique involves injecting the sample with a first syringe and a first needle inserted through the elastomer septum 210 while simultaneously venting air from the sample space 200 with a second needle inserted through the elastomer septum 210. This two-needle method ensures complete filling of the sample space 200 while minimizing the risk of introducing air bubbles that could affect the accuracy of the measurements. After the sample space 200 is filled, the elastomer septum 210 self-seals, and the space is sealed with the cylindrical recess 224. This sealing process typically involves applying a layer of epoxy over the elastomer septum 210 and covering cylindrical recess 226 with cylindrical recess 224, providing a strong and durable seal that prevents leakage or evaporation of the sample. To mount the sample holder in a magnetometer, the holder can be threaded onto the instrument’s sample rod, ensuring secure and precise positioning within the magnetic field. The magnetometry measurement can involve various techniques, depending on the specific instrument being used and the magnetic properties of interest. A common approach is to measure the magnetic moment of the liquid sample in response to an applied magnetic field, generating a hysteresis loop that provides information about the sample’s magnetization behavior. During the measurement, it can involve determining the center position of the liquid sample, particularly when using instruments like SQUID-VSMs where accurate positioning is critical. This can be accomplished using a centering algorithm, which analyzes the sample’s magnetic response to identify its precise location within the detection coils. Based on the determined center position, the position of the sample holder can be adjusted to ensure optimal alignment and minimize positional errors. The method can be performed over a wide range of temperatures, from cryogenic conditions to room temperature, depending on the specific requirements of the analysis. Measurementscan be performed at temperatures from 2 K to 400 K, allowing for the investigation of the sample’s magnetic properties across a broad temperature range. In some cases, the measurement can be performed at a temperature where the liquid sample is frozen, providing insight into the magnetic behavior of the immobilized particles. The choice of magnetometer for the measurement depends on the specific properties of the sample and the desired sensitivity and resolution. The magnetometer used in the method may comprise a vibrating sample magnetometer, a superconducting quantum interference device magnetometer, or an alternating gradient magnetometer, each offering distinct advantages and limitations for analyzing magnetic materials.

[0092] These additional steps and variations enhance the method of performing magnetometry measurements of a liquid sample by providing flexibility in sample handling, ensuring accurate sample positioning, enabling measurements over a wide temperature range, and accommodating a variety of magnetometer types. The two-needle injection technique minimizes air bubbles during filling, while the epoxy sealing ensures a durable and leak-proof sample environment. The use of a centering algorithm and subsequent adjustment of the holder’s position improves measurement accuracy, while the ability to perform measurements at different temperatures, including when the sample is frozen, expands the versatility of the method for analyzing diverse magnetic fluids. The option to use different types of magnetometers further broadens the applicability of the method, allowing for the characterization of a wide range of magnetic materials and properties.

[0093] The next step in the method involves injecting the liquid sample into the cylindrical sample space 200 of the holder through the elastomer septum 210. This injection process can be performed using a syringe and a needle, carefully inserted through the septum 210 to minimize damage and ensure a tight seal after withdrawal. To facilitate complete filling and prevent the formation of air bubbles, a two-needle technique can be employed. This involves simultaneously injecting the sample with a first syringe and a first needle while venting air from the sample space 200 through a second needle. The second needle allows for the escape of displaced air as the liquid sample is introduced, ensuring a uniform and bubble-free sample environment. After the sample space 200 is filled, the needles are carefully withdrawn, and the elastomerseptum 210, due to its self-sealing properties, closes tightly, minimizing the risk of contamination and enabling the preparation of air-sensitive samples.

[0094] Once the liquid sample has been injected into the sample space 200, the next step involves sealing the space with the cylindrical cover 224. This sealing process can involve applying a layer of epoxy over the elastomer septum 210 and the surrounding surface of the holder and then covering cylindrical recess 226 with cylindrical recess 224. The epoxy is carefully applied to ensure a complete and uniform seal, preventing any leakage or evaporation of the sample. The epoxy then cures, forming a hard, durable barrier that maintains the integrity of the sample space 200, even when the holder is placed under vacuum or subjected to temperature changes. This cylindrical recess 224, in conjunction with the elastomer septum 210, ensures that the sample remains contained within a defined volume and maintains a consistent geometry throughout the magnetometry measurement, contributing to the accuracy and reliability of the analysis.

[0095] After the sample space 200 is securely sealed, the liquid sample holder 201 is mounted within the magnetometer, ensuring precise and consistent positioning of the sample for analysis. This mounting process involves threading the holder onto the instrument’s sample rod, taking advantage of the threaded post 232 incorporated into the holder design. This threaded connection provides a secure and stable mount, minimizing positional errors that could affect the accuracy of the magnetometry measurement. Once the holder is securely mounted, it is positioned within the sensitive region of the magnetometer, allowing the sample to interact with the instrument’s magnetic field.

[0096] With the liquid sample holder 201 securely mounted within the magnetometer, the method involves performing a magnetometry measurement of the liquid sample. This measurement process involves applying a controlled magnetic field to the sample and measuring its magnetic response, typically in terms of its magnetic moment. The specific measurement techniques and parameters employed will depend on the type of magnetometer being used and the magnetic properties of interest. For example, SQUID magnetometers measure the change in magnetic flux as the sample is moved through a set of superconducting detection coils, while VSMs measure the voltage induced in a coil as the sample vibrates within a magnetic field. The dataobtained from these measurements can be used to generate hysteresis loops, providing information about the sample’s magnetization behavior, including its saturation magnetization, remanence, and coercivity. Additional analysis of the data can provide insights into the sample’s magnetic anisotropy, particle size distribution, and other magnetic properties. The precise control over the sample’s geometry and position afforded by the liquid sample holder 201 , coupled with the ability to perform measurements at different temperatures and using various magnetometer types, enables the comprehensive and accurate characterization of magnetic fluids.

[0097] The process of performing a magnetometry measurement of the liquid sample involves a carefully orchestrated interplay between the magnetometer’s hardware and software, enabling the acquisition of precise data that reveals the sample’s magnetic properties. A controlled magnetic field, generated by either superconducting magnets or electromagnets, is applied to the sample, and its magnetic response is measured using sensitive detection coils. The specific configuration of these coils, often in a second-derivative arrangement, is designed to eliminate contributions from background fields and gradients, ensuring that the measured signal is primarily due to the sample’s magnetic moment.

[0098] The magnetometer’s software involves controlling the applied field, acquiring the signal from the detection coils, and performing the necessary data analysis. The applied field can be varied over a wide range, from a few milli Tesla to several tesla, allowing for the investigation of the sample’s magnetic behavior at different field strengths. Algorithms can be used for processing the raw data, correcting for background signals, and calculating the sample’s magnetic moment. In instruments like SQUID-VSMs, where the sample vibrates about a central position, the software may also include algorithms for determining the sample’s center position and dynamically adjusting its position to ensure optimal alignment within the detection coils.

[0099] The acquired data can be analyzed in various ways to extract information about the sample’s magnetic properties. A common approach is to generate hysteresis loops, which depict the magnetic moment of the sample as a function of the applied magnetic field. These loops provide a visual representation of the sample’s magnetization behavior, revealing key parameters such as its saturationmagnetization, remanence, and coercivity. Further analysis of the data can yield information about the sample’s magnetic anisotropy, particle size distribution, and other magnetic characteristics. The software often includes tools for fitting the data to theoretical models, enabling the extraction of quantitative parameters that describe the sample’s magnetic behavior.

[0100] The ability to accurately control the applied field, acquire high- resolution data, and perform sophisticated data analysis is crucial for revealing the subtle magnetic properties of fluid samples. The liquid sample holder 201 , by minimizing artifacts and ensuring consistent sample positioning, enhances the quality of the acquired data and enables the reliable extraction of meaningful information about the sample’s magnetic behavior.

[0101] In an embodiment, with reference to FIG. 2, a comprehensive analysis of the magnetic properties of various materials considered for use in constructing the liquid sample holder 201 is presented, demonstrating the relevance of selecting materials that minimize background magnetic signals and ensure compatibility with the target fluid samples. The figure displays magnetic measurement data for nine different materials, including polymers, elastomers, adhesives, and epoxies. Each material’s magnetic moment is plotted as a function of the applied magnetic field at two different temperatures, 300 K and 5 K, representing room temperature and cryogenic conditions, respectively.

[0102] The data for FFKM, a carbon black-filled perfluoroelastomer, reveals a weak diamagnetic response at both 300 K and 5 K, indicating its suitability for use as an elastomer septum in the liquid sample holder 201 . PCTFE, the material chosen for the main body of the holder, also exhibits weak diamagnetism at both temperatures, highlighting its low magnetic susceptibility and suitability for minimizing background signals. Silicone / PTFE, another potential elastomer septum material, displays similar weak diamagnetic behavior. The epoxy used to seal the rigid cover exhibits a slightly stronger diamagnetic response at 300 K, but its signal remains relatively low. Several other materials, including glass-filled polycarbonate, polycarbonate, acrylic, and PVC, show more complex magnetic behavior, with some displaying paramagnetism at low temperatures. These results demonstrate the importance of careful material selection for constructing the liquid sample holder 201 ,as stronger magnetic signals from the holder itself can obscure the signal from the fluid sample and introduce artifacts.

[0103] By presenting the magnetic properties of various materials at different temperatures, FIG. 2 guides the selection of appropriate materials for the liquid sample holder 201 , ensuring minimal magnetic interference and compatibility with the target fluid samples. The figure demonstrates that FFKM, PCTFE, silicone / PTFE, and epoxy exhibit weak diamagnetism, making them suitable choices for minimizing background signals. The data also highlights the need to consider temperature effects on material properties, as some materials display significant changes in magnetic behavior at low temperatures. This information enables the design of a holder that minimizes artifacts and enables accurate magnetometry measurements over a wide range of temperatures and fluid types.

[0104] FIG. 3 provides an analysis of the magnetic behavior of an empty liquid sample holder 201 , demonstrating its minimal background signal and excellent thermal stability, prerequisites for accurate magnetometry measurements of fluid samples. The figure presents data obtained from SQUID magnetometry measurements of the holder at two different temperatures, 300 K and 5 K, representing room temperature and cryogenic conditions, respectively. The data includes both the magnetic moment of the holder, measured in units of A-m2, and the change in the holder’s center position, denoted as Ad and measured in millimeters, both as a function of the applied magnetic field.

[0105] At 300 K, the empty sample holder exhibits a weak diamagnetic response, as expected from the choice of PCTFE as the holder material. The magnetic moment signal is smooth and linear, indicating a consistent and predictable response to the applied field. The small magnitude of the signal, on the order of 10’6A-m2, highlights the holder’s low magnetic susceptibility and its ability to minimize background contributions that could interfere with the measurement of the fluid sample. The center position data at 300 K shows a relatively constant value at high and moderate fields, indicating good positional stability. A shift in the center position is observed at low fields, likely due to the varying magnetic responses of the different materials that constitute the holder’s boundaries (PCTFE, elastomer septum, and epoxy).

[0106] At 5 K, a weak paramagnetic signal is observed, likely due to the presence of trace amounts of oxygen in the empty sample space. This signal is nearly linear and remains relatively weak, demonstrating that even at cryogenic temperatures, the holder’s background contribution is minimal. The center position data at 5 K shows a small offset compared to the 300 K data, indicating minimal thermal contraction of the sample holder and good thermal stability. A shift in center position is also observed at low fields, likely due to the combined effects of the paramagnetic oxygen signal and the temperature-dependent magnetic properties of the holder materials.

[0107] FIG. 3, by presenting the magnetic moment and center position data for an empty liquid sample holder 201 at different temperatures, demonstrates its minimal background signal and excellent thermal stability, factors for ensuring accurate and reliable magnetometry measurements of fluid samples. The weak diamagnetic response at 300 K, coupled with the small paramagnetic signal at 5 K, highlights the holder’s low magnetic susceptibility, minimizing background contributions. The consistent center position data at both temperatures demonstrates good positional and thermal stability, ensuring accurate and reproducible measurements over a wide range of conditions.

[0108] FIG. 4 demonstrates the effectiveness of the liquid sample holder 201 in minimizing measurement artifacts caused by sample movement and shape changes, enabling the accurate characterization of magnetic fluids. The figure presents data obtained from SQUID-VSM measurements of a water-based magnetic fluid sample contained within the holder. The data includes both the magnetic hysteresis loops, depicting the magnetic moment of the sample as a function of the applied magnetic field, and the change in the sample’s center position, denoted as Ad, both measured at 300 K (liquid state) and 200 K (frozen state).

[0109] At 300 K, three consecutive measurements (Runs 1-3) are shown, each displaying a well-defined hysteresis loop with minimal noise, indicating consistent and reliable data. The overlapping nature of the loops demonstrates the repeatability of the measurements, highlighting the holder’s ability to maintain a stable sample environment. The center position data at 300 K reveals a small variation during the measurement, likely due to the movement of magnetic particles within the fluid inresponse to the applied field. Notably, the initial center position of the sample at 0 T differs from the center position measured at the same field after the application and removal of higher fields. This history dependence suggests the formation of particle aggregates or chains at high fields that persist even after the field is removed, leading to a shift in the sample’s center position. However, the magnitude of this center position change is significantly smaller than that observed in conventional holders, demonstrating the effectiveness of the liquid sample holder 201 design in minimizing sample movement.

[0110] The data obtained at 200 K, when the sample is frozen, further emphasizes the holder’s ability to maintain a stable sample environment and minimize artifacts. The center position data at 200 K remains nearly constant throughout the measurement, with only minor deviations likely due to instrument noise. This stability contrasts with the variations observed at 300 K when the sample is in a fluid state, confirming that the center position changes observed at 300 K are primarily due to sample movement rather than artifacts associated with the holder itself.

[0111] FIG. 4, showing the hysteresis loops and center position data for a magnetic fluid sample measured in both liquid and frozen states, highlights the effectiveness of the liquid sample holder 201 in minimizing artifacts and ensuring the accuracy of magnetometry measurements. The consistent and repeatable hysteresis loops obtained at 300 K demonstrate the holder’s ability to maintain a stable sample environment, while the reduced variations in center position compared to conventional holders highlight its effectiveness in minimizing sample movement. The nearly constant center position data at 200 K further confirms that the holder itself contributes minimally to measurement artifacts, enabling the accurate characterization of magnetic fluids.

[0112] The use of the novel liquid sample holder 201 provides significant advantages and benefits in obtaining high-quality magnetometry data of fluid samples compared with conventional holders. Conventional holders, often designed primarily for solid samples, fail to address the inherent mobility and shape-changing tendencies of liquids, leading to significant measurement artifacts. These artifacts can stem from changes in the sample’s center position, shape, and particle distribution duringanalysis, obscuring important features of the hysteresis loop and leading to inaccuracies in the measured magnetic moment.

[0113] The liquid sample holder 201 , with its specialized design features, mitigates these issues, enabling more accurate and reliable characterization of magnetic fluids. The cylindrical sample space, coupled with the hollow extensions, minimizes shape-related distortions of the magnetic field and reduces end effects, resulting in more precise magnetic moment measurements. The elastomer septum allows for complete filling of the sample space without trapping air bubbles, ensuring a uniform sample environment and enabling the analysis of air-sensitive materials. The rigid cover maintains the holder’s structural integrity, preventing deformation or leakage of the sample even under vacuum or during temperature changes. This arrangement ensures a consistent sample geometry throughout the measurement, contributing to improved data quality and repeatability.

[0114] Furthermore, the liquid sample holder 201 facilitates the precise positioning of the sample within the magnetometer, minimizing positional errors that can significantly affect measurement accuracy. The ability to perform measurements at various temperatures, including cryogenic conditions, expands the range of applications and enables the investigation of temperature-dependent magnetic phenomena. The compatibility of the holder with different types of magnetometers further enhances its versatility, allowing for the selection of the most appropriate instrument based on the specific properties of the fluid sample. By addressing the challenges associated with analyzing fluid samples, the liquid sample holder 201 enables the acquisition of high-quality magnetometry data, advancing the understanding and characterization of magnetic fluids.

[0115] The articles and processes herein are illustrated further by the following Example, which is non-limiting.EXAMPLE

[0116] Liquid Sample Holder for Optimal Fluid Magnetic Measurements

[0117] Magnetic fluids have been the subject of intense research for several decades due to their numerous applications as well as for their fundamental science. Commercial magnetometers are accurate and well-characterized for solid and powder samples, but artifacts can occur in magnetic measurements of fluid samples. These artifacts originate primarily from the dynamic nature of the sample center position, size, shape, and particle distribution. This Example describes a sample holder that minimizes the motion of the fluid sample during measurement, significantly reducing these artifacts. Additional considerations in the design that minimize magnetic signals from the sample holder itself include choice of sample holder material and shape. Experimental data demonstrating the effectiveness of the new design, including background signal, are presented.

[0118] Magnetic micro- and nano-particles have been the subject of research due to their unique properties and behavior (e.g., superparamagnetism) as well as an increasing range of applications (e.g., in biomedicine, dampers, etc.). Currently, magnetic characterization is done on dried samples of magnetic particles, or magnetic particles embedded in a rigid matrix such as epoxy or paraffin wax. However, to understand the behavior of magnetic micro- or nano-particles, including the effects of dynamic interparticle interactions, the magnetic characterization must be done in the fluid form.

[0119] Commercial magnetometers are characterized for solid and powder samples although artifacts exist that affect accuracy. However, magnetic measurements of fluid samples are susceptible to several additional measurement artifacts. These artifacts arise from the fluid nature of the sample, which allows changes in the size, shape, center position, and particle distribution of the sample during measurement. Observed errors in measurements of fluid samples have been due to changes in the sample center position during measurement. This is expected, given that many magnetic measurement techniques, such as the vibrating sample magnetometer (VSM), rely on a well-defined center position for the sample. This center position can be determined at the beginning of a measurement, and for solid samples is only reassessed after significant changes, such as large changes in the temperature. In the measurements, a change in sample position of 2.7 mm resulted in a 44% reduction in the measured magnetic moment. The exact error depends on thegeometry of the system, and increases approximately quadratically with the change in sample position. Even when the sample center position is determined at each data point so that these errors are avoided, errors may arise due to changes in the sample shape or particle distribution. In the measurements, a change in in the sample shape of a fluid sample resulted in a 7% error in the measured magnetic moment. There is also the potential for artifacts from nanoparticles immobilized during the sealing of the sample holder (e.g., with epoxy), creating a heterogeneous sample. This is a concern in fluids where the particles are made of a hard magnetic material, resulting in the remanance of the immobilized particles overwhelming the signal from the mobile particles in the fluid, which might otherwise be randomized at zero field due to Brownian motion.

[0120] A sample holder that is optimally designed for fluid samples can minimize the effects of these possible sources of error. This Example describes a fluid sample holder specifically designed for fluid samples that mitigates or eliminates the artifacts due to the fluid nature of the sample.

[0121] Design of Sample Holder

[0122] The design parameters for the liquid sample holder included: sample dimensions that are: within recommended range for the instrument on which it will be used; and (b) sufficiently small to minimize artifacts and sufficiently large to provide a good signal and good signal-to-noise ratio; the magnetic signal due to sample holder is minimized, wherein the liquid sample holder: (a) includes diamagnetic materials for the sample holder to minimize background magnetic signal; and (b) minimizes magnetic signal due to geometry of sample holder (e.g., end effects); fill the sample space completely to minimize sample movement (e.g., removal of air bubbles and eliminate changes in sample shape); pre-seal the sample holder to avoid immobilization of particles in sealant (e.g., eliminate heterogeneity); the materials of construction are compatible with solvents commonly used in magnetic fluids; and the sample holder is structurally sound: (a) over a selected temperature range (1.5 K < T < 400 K ), even after solvent crystallization, and while minimizing thermal mass; and (b) vacuum tight.

[0123] The dimensions of the liquid sample holder depend on the magnetometer it will be used with. The liquid sample holder was designed to work with commercially available magnetometers, including the MPMS DC SQUID by Quantum Design, the MPMS3 SQUID-VSM by Quantum Design, and the MicroSense Model 10 VSM. A sample size less than, e.g., 5 mm works. It is contemplated that, beyond this size, significant errors can occur.

[0124] The design is shown in FIG. 1. A photograph of the prototype is shown in (a) filled with magnetic fluid (dark region). A model of the sample holder is shown in (b). The outer diameter of the sample holder is 6.0 mm . The inner diameter (diameter of the sample space) is 3.45 mm and the height of the sample space is 4.0 mm . A detailed engineering drawing is shown in FIG. 5.

[0125] The sample space is a cylinder, which provides a defined geometry. Another shape is a spherical liquid container, and it is difficult to make perfectly spherical in practice. The effective demagnetizing factor of a magnetic fluid depends not only on the shape of the macroscopic sample but also the shape of the individual particles and any aggregates, weighted by the concentration of particles / aggregates. Therefore, the effective demagnetizing factor of most dilute magnetic fluids depends only weakly on the shape of the sample container.

[0126] To fill the sample holder completely without immobilizing any particles in the seal, we utilized an elastomer septum. This elastomer septum can and should be glued onto the sample holder prior to loading the fluid sample. The fluid sample is injected through the septum with a narrow needle and a second needle allows air to escape, as shown in FIG. 1 (c). The elastomer septum is self-sealing, closing on its own when the needle is removed. One benefit of this design is that it would be effective for preparing fluid samples that are air / oxygen sensitive. The air can be exchanged with an inert gas while loading into a glove box; once the sample is loaded inside the glove box, the needles should be removed to seal the sample holder. However, the elastomer septum cannot be considered structurally rigid under vacuum or during / after sample freezing. Therefore, the top portion of the holder is epoxied over the septum for additional security and rigidity. A slightly rough surface where the top and bottom portions contact can provide a good epoxy seal. Otherwise, some torque can break the binding.

[0127] A feature of the design is the hollow extensions on the top and bottom, where the inner diameter of these extensions is the same as that of the sample space. These extensions avoid end effects that cause false magnetic signals due to an inhomogeneous background, from the ends of the sample holder when they enter or pass through the pick-up coils. Solid extensions can serve the same purpose and might increase the thermal mass resulting in longer times to achieve temperature accuracy and stability. By making them hollow, one balance thermal mass, end effects, and structural integrity. The length of the hollow ends can be varied depending on the specifications of the magnetometer. For an alternating gradient magnetometer (AGM) where the holder mass matters, the hollow ends can be removed. Only the liquid capsule portion, including the elastomer septum and its cover, can be used.

[0128] A variety of materials were considered for use in the sample holder. These materials must be diamagnetic (to minimize the background) and structurally rigid over the desired temperature range ( 1.5 K < T < 400 K ) and under vacuum and with the internal pressure from freezing / crystallization of the fluid. To ensure that the materials did not have a spurious magnetic signal, we measured the magnetic moment of samples of each material (see FIG. 2). For the main components of the sample holder, we considered glass-filled polycarbonate (GFP), polycarbonate, acrylic, polyvinyl chloride (PVC), and polychlorotrifluoro-ethylene (PCTFE) as these all had good structural integrity. Polytetrafluoroethylene (PTFE) was not considered because it is not rigid enough to be structurally sound. We also considered both silicone / PTFE and a carbon black-filled perfluoroelastomer (FFKM) as potential elastomer septum materials. Finally, we considered an epoxy and an instant adhesive for use as sealing materials. These materials except glass-filled polycarbonate were found to be weakly diamagnetic, which is ideal for magnetic measurements.

[0129] Another material parameter to consider is solvent compatibility. Many nanoparticle suspensions use solvents such as hexane, dichlorobenzene, toluene, acetone, etc. In terms of the materials used for the top and bottom parts of the sample holder, PCTFE has good resistance to the relevant solvents for magnetic nanoparticles. For solvent compatibility of elastomers, the FFKM is far superior to silicone, however silicone is easier to work with. For these reasons, we chose PCTFEfor the sample holder. For the elastomer septum, silicone / PTFE can be used for waterbased samples while FFKM should be used for other solvents.

[0130] Various components involved for sample mounting can include: top and bottom of sample holder, machined from PCTFE; elastomer septum, cut to 4.75 mm diameter with an arch punch; two-part glue (primer and instant adhesive); epoxy (extra fast setting); 1 ml syringe; and 30G syringe needles.

[0131] The sample mounting procedure includes: sealing the septum in place in the sample holder, as shown in FIG. 1 (c) using two-part glue; applying primer followed by adhesive to both the sidewalls and shelf portion of the sample holder before inserting septum to ensure adequate attachment; drying the adhesive; determining the mass of the bottom part of sample holder with mounted septum; injecting a liquid sample through septum into sample holder with one syringe and needle, wherein a second needle to allow air to escape, as shown in FIG. 1 (c); removing air from inside, while tracking the fluid injected; removing the needles; determining a mass of the bottom of the liquid sample holder with septum and sample to find the total mass of injected sample plus sample holder and subtracting this mass from the prior determined mass; combining epoxy and disposing the epoxy over the septum and sidewalls on bottom of the liquid sample holder and inside cup on top of holder; disposing the top of the liquid sample holder over the bottom; removing excess epoxy; and curing the epoxy to allow outgas solvent.

[0132] Magnetic Measurements with the Liquid Sample Holder

[0133] The background signal from the liquid sample holder was determined from magnetic measurements performed in a SQUID-VSM, and the raw data was modeled to extract the magnetic moment. FIG. 3(a) shows the background signal of the empty sample holder at 300 K and 5 K and (b) shows the center position. At 300 K , the holder is weakly diamagnetic as expected. At 5 K , due to the presence of air including oxygen in the empty sample space, a weak paramagnetic signal is present. However, both of these signals are smooth and linear (at 300 K ) or nearly linear (at 5 K ) and weak ( 10-6A - m2[10-3emu] ). Therefore, the magnetic background contribution can be easily removed. Furthermore, the center position Ad is nearly constant at high and moderate fields (> 1.5 T). At low fields, there is some variationin the center position, but this is not meaningful in this case because there is no magnetic sample to center on (m < 2 x 10-7A • m2). The significant magnetic signals at 300 K come from the top and bottom boundaries of the sample space, which are made of PCTFE (bottom) and a combination of PCTFE, elastomer (silicone / PTFE or FFKM), and epoxy (top). These materials are all diamagnetic at 300 K (see Figure 2), however the relative strengths of the diamagnetic moments of the different materials leads to a shift in the center position Ad from the top to the bottom, as shown by the shape of the data at .0H > 1 T. At 5 K , the sample rod contracts leading to a center change of less than 1 mm , as shown by the offset, which indicates good thermal stability (low thermal contraction, < 1% ). At 5 K the center position also undergoes a shift at low field, which is in a different direction from the 300 K data, and smaller in magnitude, due to the paramagnetic oxygen signal as well as the different magnetization behavior of the sample holder materials at 5 K (FIG. 2). In addition, there is a bifurcation in center position at low fields which can be explained by the center being located at either the top or bottom boundary of the sample space. Upon cycling from 5 K , we find that the sample holder is structurally sound, as desired.

[0134] The sample holder was filled with a magnetic fluid sample. FIG. 4(a) shows data from a water-based magnetic fluid sample with solid content of 25 mg per mL. The sample was measured three times at 300 K and the measured magnetic moment was consistent for all three runs. The center position (FIG. 4(b)) varied slightly during the measurement, which is expected due to motion of the magnetic particles in the colloid as a field is applied. In particular, note that the initial center position of the sample at the beginning of Run 1 , in a field of 0 T , differs from the center position measured at later times at the same field; thus, the center position is dependent on the magnetic history of the sample. This can be due to formation of linear chains of particles with strong interparticle interactions at high fields. When the field is decreased following the formation of such chains, particle aggregates remain which then sediment to the bottom of the sample. Further application of high fields reinstates the linear chains which extend through the entire sample space. It should be noted that the change in center position in this new sample holder is significantly smaller (about 1 mm ) than in previous measurements (about 2 mm ), due to the smaller sample space ( 4 mm height rather than about 7 mm height).

[0135] Because it may not be possible to prevent the center from shifting with the change in applied magnetic field, dynamic centering (either during the measurement if the moment is sufficiently strong or after by fitting of the raw data) is involved to measure an accurate moment. In this case, the raw data clearly fit the model across all applied fields, so the point dipole assumption is satisfied with this geometry, and no unexpected sample movements occur. Therefore, the hysteresis loops under different measurement / centering conditions overlap. The new design removes sample holder artifacts, so that the moment saturates (rather than having a diamagnetic / paramagnetic slope) without arbitrary background subtractions. Furthermore, for the low field regime, there is no evidence of any change in coercivity due to immobilization of the nanoparticles. The sample holder is also structurally stable even when freezing the liquid during thermal cycling, as desired.

[0136] Measurements were repeated on the water-based magnetic fluid at 200 K where the water is solid and the nanoparticles are fully immobilized, and data are shown in FIG. 4(c). The dynamic center position is within 1<J for almost all the measurements, with a couple of outliers (with very low moment) which are within 2<J or 3<J. This demonstrates that the center changes shown in FIG. 4(b) are due to the sample and not due to the liquid sample holder.

[0137] Magnetic moment measurements of fluid samples can be complicated by artifacts due to the fluid nature of the samples. These artifacts can be minimized by the use of an appropriate sample holder. The liquid sample holder designed specifically for fluid samples accounts for the potential sources of error. Changes in the particle distribution in the fluid (due to chaining, settling, etc.) can occur. Therefore, dynamic centering or fitting of raw data can provide accurate measurements.

[0138] While one or more embodiments have been shown and described, modifications and substitutions can be made thereto without departing from the spirit and scope of the invention. Accordingly, it is to be understood that the present invention has been described by way of illustrations and not limitation. Embodiments herein can be used independently or can be combined.

[0139] All ranges disclosed herein are inclusive of the endpoints, and the endpoints are independently combinable with each other. The ranges are continuous and thus contain every value and subset thereof in the range. Unless otherwise stated or contextually inapplicable, all percentages, when expressing a quantity, are weight percentages. The suffix (s) as used herein is intended to include both the singular and the plural of the term that it modifies, thereby including at least one of that term (e.g., the colorant(s) includes at least one colorants). Option, optional, or optionally means that the subsequently described event or circumstance can or cannot occur, and that the description includes instances where the event occurs and instances where it does not. As used herein, combination is inclusive of blends, mixtures, alloys, reaction products, collection of elements, and the like.

[0140] As used herein, a combination thereof refers to a combination comprising at least one of the named constituents, components, compounds, or elements, optionally together with one or more of the same class of constituents, components, compounds, or elements.

[0141] All references are incorporated herein by reference.

[0142] The use of the terms “a,” “an,” and “the” and similar referents in the context of describing the invention (especially in the context of the following claims) are to be construed to cover both the singular and the plural, unless otherwise indicated herein or clearly contradicted by context. It can further be noted that the terms first, second, primary, secondary, and the like herein do not denote any order, quantity, or importance, but rather are used to distinguish one element from another. It will also be understood that, although the terms first, second, etc. are, in some instances, used herein to describe various elements, these elements should not be limited by these terms. For example, a first current could be termed a second current, and, similarly, a second current could be termed a first current, without departing from the scope of the various described embodiments. The first current and the second current are both currents, but they are not the same condition unless explicitly stated as such.

[0143] The modifier about used in connection with a quantity is inclusive of the stated value and has the meaning dictated by the context (e.g., it includes thedegree of error associated with measurement of the particular quantity). The conjunction or is used to link objects of a list or alternatives and is not disjunctive; rather the elements can be used separately or can be combined together under appropriate circumstances.PARTS LIST cylindrical sample space 200 liquid sample holder 201 first end 202 second end 204 hollow extension 206 hollow extension 208 elastomer septum 210 attachment point 214 air holes 216 top portion 220 bottom portion 222 cylindrical recess 224 cylindrical cavity 226 shelf 230 threaded post 232 performing magnetometry measurements

Claims

What is claimed is:

1. A liquid sample holder for magnetometry measurements, comprising: a cylindrical sample space 200 for receiving a liquid sample, the sample space 200 having a first end 202 and a second end 204; an optional hollow extension 206 extending from the first end 202 of the sample space 200, the hollow extension 206 having an internal diameter substantially equal to an internal diameter of the sample space 200; an optional hollow extension 208 extending from the second end 204 of the sample space 200, the hollow extension 208 having an internal diameter substantially equal to the internal diameter of the sample space 200; an elastomer septum 210 sealing the sample space 200; and a rigid cover 212 sealing the elastomer septum 210.

2. The liquid sample holder of claim 1 , wherein the sample space 200 has an inner diameter from 2 mm to 4 mm.

3. The liquid sample holder of claim 2, wherein the sample space 200 has a height from 3 mm to 5 mm.

4. The liquid sample holder of claim 1 , wherein the sample space 200, the hollow extension 206, and the hollow extension 208 are formed as a unitary structure.

5. The liquid sample holder of claim 1 , wherein the elastomer septum 210 comprises a material selected from the group consisting of silicone / PTFE and a carbon black-filled perfluoroelastomer (FFKM).

6. The liquid sample holder of claim 1 , wherein the cylindrical recess 224can be sealed with epoxy.

7. The liquid sample holder of claim 1 , further comprising: an attachment point 214 for attaching the holder to a sample rod of a magnetometer.

8. The liquid sample holder of claim 7, wherein the attachment point 214 comprises a threaded post for threaded engagement with the sample rod.

9. The liquid sample holder of claim 1 , wherein the liquid sample holder comprises polychlorotrifluoroethylene (PCTFE).

10. The liquid sample holder of claim 1 , further comprising: a plurality of air holes 216 disposed in the top portion of the sample holder, the air holes 216 adapted to allow release of air during sealing of the sample.

11. A method of performing magnetometry measurements of a liquid sample, comprising: providing a liquid sample holder comprising a cylindrical sample space 200 for receiving a liquid sample, the sample space 200 having a first end 202 and a second end 204; a hollow extension 206 extending from the first end 202 of the sample space 200, the hollow extension 206 having an internal diameter substantially equal to an internal diameter of the sample space 200; a hollow extension 208 extending from the second end 204 of the sample space 200, the hollow extension 208 having an internal diameter substantially equal to the internal diameter of the sample space 200; an elastomer septum 210 sealing the sample space 200; and a cylindrical recess 224sealing the elastomer septum 210; injecting a liquid sample into the sample space 200 of the holder through the elastomer septum 210; sealing the sample space 200with the cylindrical recess 224; mounting the sample holder in a magnetometer; and performing a magnetometry measurement of the liquid sample.

12. The method of claim 11 , wherein the injecting comprises: injecting the liquid sample with a first syringe and a first needle inserted through the elastomer septum 210; and venting air from the sample space 200 with a second needle inserted through the elastomer septum 210.

13. The method of claim 11 , wherein the sealing the sample space 200 comprises applying epoxy over the elastomer septum 210.

14. The method of claim 11 , wherein the mounting the sample holder in a magnetometer comprises: threading the sample holder onto a sample rod of the magnetometer.

15. The method of claim 11 , wherein the performing a magnetometry measurement comprises: measuring a magnetic moment of the liquid sample in response to an applied magnetic field.

16. The method of claim 15, further comprising: determining a center position of the liquid sample during the measurement.

17. The method of claim 16, further comprising: adjusting a position of the sample holder to a determined center position of the liquid sample.

18. The method of claim 11 , wherein the performing a magnetometry measurement comprises performing a measurement at a temperature between 5 K and 300 K.

19. The method of claim 11 , wherein the performing a magnetometry measurement comprises performing the measurement at a temperature where the liquid sample is frozen.

20. The method of claim 11 , wherein the magnetometer comprises a vibrating sample magnetometer, a superconducting quantum interference device magnetometer, or an alternating gradient magnetometer.

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