Application of cebr3 single crystal in adiabatic demagnetization refrigeration

Abstract

The application discloses application of a CeBr3 single crystal in adiabatic demagnetization refrigeration; the material does not need to introduce crystal water, has strong cryogenic refrigeration capacity, in addition, the material has a small characteristic critical magnetic field scale, can realize effective refrigeration under a low external magnetic field condition, and significantly reduces the dependence of the system on a high magnetic field environment and high-precision magnetic field regulation.

Description

Technical Field

[0001] This invention relates to the field of cryogenic refrigeration technology, and in particular to the application of CeBr3 single crystal in adiabatic demagnetizing refrigeration. Background Technology

[0002] Existing cryogenic adiabatic demagnetization refrigeration technologies can be mainly categorized into two types. The first type is the adiabatic demagnetization refrigeration scheme using traditional paramagnetic materials. This type of scheme typically uses paramagnetic salt materials as the refrigerant, such as ferric ammonium sulfate (FeNH4(SO4)2·12H2O) and chromium potassium alum (CrK(SO4)2·12H2O). To effectively reduce the interaction between magnetic ions and delay the emergence of magnetic order at low temperatures, the aforementioned paramagnetic salt materials usually increase the average spacing between magnetic ions by introducing a large number of non-magnetic ions and water of crystallization. The magnetic ions are isolated by the water of crystallization molecules and their coordination structure, thereby weakening the exchange interaction between magnetic ions to a certain extent, lowering the temperature at which magnetic order appears, and improving its refrigeration performance in the cryogenic region.

[0003] However, these paramagnetic salt materials have significant shortcomings in practical applications. On the one hand, magnetic refrigerants capable of cooling at temperatures of 100 mK and below mainly rely on paramagnetic salt materials containing water of crystallization. These materials generally suffer from low thermal conductivity and easy desorption of water of crystallization, leading to crystal structure collapse under extremely low temperatures and high vacuum conditions, resulting in unstable cooling performance and limited service life. Although existing technologies have improved heat transfer performance to some extent by introducing metal heat buses, this approach requires complex and expensive packaging structures and growth processes, significantly increasing system costs and manufacturing difficulty, which is detrimental to engineering applications and large-scale promotion.

[0004] On the other hand, paramagnetic cooling materials without crystallization water (such as GGG) have certain advantages in terms of structural stability and low-temperature thermal conductivity, and overcome the encapsulation and reliability problems related to crystallization water. However, their lowest achievable cooling temperature is usually only around 500 mK, which is difficult to meet the application requirements of lower temperature ranges (especially 100 mK and below), and their cooling capacity has intrinsic limitations.

[0005] The second category comprises magnetic field-induced cooling schemes based on the quantum critical phenomenon of quantum magnetic materials. In recent years, some research has proposed utilizing the strong quantum fluctuations and enhanced magnetic entropy changes exhibited by low-dimensional frustrated quantum magnets near the magnetically induced quantum critical point to achieve adiabatic demagnetization cooling. These schemes typically employ rare-earth-based or transition metal-based low-dimensional quantum magnetic materials, using an external magnetic field to bring the system close to or through the quantum critical region, thereby achieving a significant magnetocaloric effect within a limited magnetic field range.

[0006] For quantum magnetic material cooling schemes based on quantum critical behavior, their cooling performance is typically highly dependent on the precise control and stable maintenance of the applied magnetic field within a finite critical magnetic field range. Once the magnetic field deviates from the critical region, the change in magnetic entropy weakens rapidly, and the cooling efficiency decreases significantly, which places high demands on the stability and control precision of the magnetic field. Furthermore, some existing quantum magnetic materials still require a high applied magnetic field strength within their effective cooling temperature range, which is detrimental to the miniaturization, low power consumption, and practical engineering applications of the cooling system.

[0007] Therefore, there is an urgent need to develop a new type of thermally insulating and demagnetizing refrigeration material system that does not require crystallization water, has a stable structure, and can achieve refrigeration in the temperature range of 100 mK and below. Summary of the Invention

[0008] This invention aims to at least solve one of the technical problems existing in the prior art. To this end, the first aspect of this invention proposes the application of CeBr3 single crystal in adiabatic demagnetizing refrigeration. This material does not require the introduction of water of crystallization, has strong ultra-low temperature refrigeration capability, and, in addition, the characteristic critical magnetic field scale corresponding to this material is small, which can achieve effective refrigeration under low external magnetic field conditions, significantly reducing the system's dependence on high magnetic field environment and high-precision magnetic field control.

[0009] A second aspect of the present invention also provides a magnetic refrigeration method based on CeBr3 single crystal.

[0010] A third aspect of the present invention also provides a magnetic refrigeration device.

[0011] The application of CeBr3 single crystal in adiabatic demagnetizing refrigeration according to a first aspect of the present invention.

[0012] According to a preferred embodiment of the present invention, the CeBr3 single crystal is used in cryogenic thermal adiabatic demagnetization refrigeration.

[0013] According to a preferred embodiment of the present invention, the extremely low temperature is ≤100mK.

[0014] According to a preferred embodiment of the present invention, the extremely low temperature is ≤80mK.

[0015] According to a preferred embodiment of the present invention, the extremely low temperature is ≤45mK.

[0016] According to a preferred embodiment of the present invention, the CeBr3 single crystal is a single crystal with magnetic anisotropy.

[0017] According to a preferred embodiment of the present invention, the application includes achieving cooling by adjusting the magnetic entropy of the CeBr3 single crystal by changing the strength of an applied magnetic field.

[0018] According to a preferred embodiment of the present invention, the application modulates the magnetic entropy by changing the orientation of the CeBr3 single crystal relative to the direction of the applied magnetic field, thereby achieving rotational adiabatic demagnetization refrigeration.

[0019] According to a preferred embodiment of the present invention, the rotating adiabatic demagnetizing cooling process includes: under near-adiabatic conditions and with the applied magnetic field strength remaining constant, the CeBr3 single crystal is changed from the crystal axis direction with a higher degree of magnetization to the crystal axis direction with a lower degree of magnetization relative to the magnetic field direction, thereby increasing the magnetic entropy of the system. Under the condition that the total entropy remains unchanged under adiabatic conditions, the lattice entropy decreases, thereby achieving a temperature drop.

[0020] According to a preferred embodiment of the present invention, the crystal axis direction with higher magnetization is the c-axis direction of the CeBr3 single crystal, and the crystal axis direction with lower magnetization is the a-axis direction of the CeBr3 single crystal.

[0021] According to a preferred embodiment of the present invention, the CeBr3 single crystal is obtained by purchasing commercially available materials or by preparing it using the vertical Bridgman process.

[0022] According to a preferred embodiment of the present invention, the terminal field in which the application is located includes quantum computing hardware, superconducting detectors, astronomical and space exploration payloads, or low-temperature physics experimental platforms.

[0023] The application of the embodiments of the present invention has at least the following beneficial effects: Research on CeBr3 has primarily focused on its single-crystal growth process and its application in scintillator radiation detectors, with an emphasis on improving detection performance parameters such as light yield, energy resolution, and time response. However, this research paradigm, centered on room-temperature or near-room-temperature scintillation performance, has to some extent limited the in-depth exploration of CeBr3's potential properties as a functional magnetic material. To date, the magnetocaloric properties of CeBr3 under extremely low-temperature conditions and its engineering application value have not received systematic attention.

[0024] This invention proposes a novel application of CeBr3 single crystals in cryogenic adiabatic demagnetizing refrigeration. CeBr3 contains Ce... 3+The ions possess definite local magnetic moments and a high magnetic ion density, which facilitates a large change in magnetic entropy during changes in the applied magnetic field, thereby achieving a highly efficient magnetocaloric cooling effect. Simultaneously, this material can be stably grown to obtain large-volume, high-quality single crystals, and its overall performance is significantly superior to most traditional thermal insulation and demagnetizing refrigeration materials that rely on powder pressing or composite structures. It effectively avoids inherent defects such as easy loss of crystal water under high vacuum conditions and low thermal conductivity. More importantly, the relatively weak interactions between magnetic ions in CeBr3 help suppress the formation of long-range magnetic order at low temperatures, allowing the system to maintain a large usable magnetic entropy in the milliKelvin temperature range. In summary, CeBr3 exhibits advantages such as high-quality, large-size single crystals, controllable growth, high magnetic entropy density, excellent low-temperature heat transfer performance, and good thermodynamic tunability and engineering feasibility under extremely low temperatures, demonstrating unique potential as a novel ultra-low temperature thermal insulation and demagnetizing refrigeration material.

[0025] Furthermore, this CeBr3 single-crystal material effectively suppresses the formation of low-temperature magnetic order without the introduction of water of crystallization, fundamentally avoiding the structural instability and complex encapsulation problems associated with water of crystallization. The material possesses a high magnetic ion density, significantly increasing the effective magnetic degrees of freedom available for refrigeration per unit volume, thereby improving the refrigeration capacity per unit volume. Simultaneously, the material exhibits good thermal conductivity in the low-temperature region, facilitating efficient heat removal and stable heat exchange. Moreover, the material corresponds to a relatively small characteristic critical magnetic field scale, enabling effective refrigeration under lower applied magnetic field conditions, significantly reducing the system's dependence on high magnetic field environments and high-precision magnetic field control.

[0026] Furthermore, the core reason why CeBr3 single crystals can achieve such excellent ultra-low temperature cooling performance lies directly in their unique crystal structure and the resulting special quantum state symmetry. In the crystal structure of CeBr3, each Ce ion is surrounded only by Br ions to form a coordination environment, and the local point group where the Ce ion is located has a sixth-order inversion symmetry. This highly symmetric crystal field environment imposes strict constraints on the 4f electron wavefunction of the Ce ion, resulting in an extremely pure crystal field ground state.

[0027] Calculations based on the point charge model show that, under this special symmetry protection, the crystal field double ground state of the Ce ion contains only |±5 / 2|. Instead of other mixed states, this pure ground-state property has a decisive influence on magnetic interactions: because the change in angular momentum that needs to be overcome to flip the ground-state spin is extremely large, conventional magnetic dipole interactions are prohibited by quantum selection rules. Therefore, the common dipole interaction does not exist in the system; instead, a fifth-order thirty-two-pole moment interaction occurs.

[0028] The rare-earth ion multipole moment characteristics determined by the crystal structure make CeBr3 a unique weak magnetic interaction system. Since the strength of higher-order multipole moments is much smaller than that of ordinary dipole interactions, the effective interaction energy scale within the material is significantly reduced. This allows the material to avoid spontaneous magnetic ordering at extremely low temperatures, thus generating significant magnetic entropy changes under relatively low applied magnetic fields, ultimately achieving efficient and stable cryogenic adiabatic demagnetizing refrigeration.

[0029] According to a second aspect of the present invention, a magnetic refrigeration method based on CeBr3 single crystal is provided, comprising the following steps: Using CeBr3 single crystal as the magnetic working medium, by applying and removing magnetic fields to the magnetic working medium, the temperature of the magnetic working medium changes and heat is transferred with the heat exchanger, thereby achieving the purpose of cooling.

[0030] A third aspect of the present invention provides a magnetic refrigeration device, wherein the magnetic refrigeration device includes CeBr3 single crystal as an ultra-low temperature magnetic refrigeration working fluid.

[0031] Other features and advantages of the invention will be set forth in the description which follows, and will be apparent in part from the description, or may be learned by practicing the invention. Attached Figure Description

[0032] The above and / or additional aspects and advantages of the present invention will become apparent and readily understood from the description of the embodiments taken in conjunction with the following drawings, in which: Figure 1 The Laue diffraction spot pattern of CeBr3 single crystal in the (001) crystal plane direction and its corresponding simulated diffraction pattern are shown. Figure 2 This is a graph showing the relationship between magnetization and magnetic field when an external magnetic field is applied along the c-axis of a CeBr3 single crystal at different temperatures. Figure 3 The graph shows the relationship between the magnetization of CeBr3 single crystal and the ratio of magnetic field to temperature under different temperature conditions, along with the corresponding fitting results. Figure 4 The graph shows the relationship between the magnetization intensity and the magnetic field when an external magnetic field is applied along the c-axis and a-axis of the CeBr3 single crystal at 2 K. Figure 5 The graph shows the relationship between the magnetic specific heat of CeBr3 single crystal and temperature under different applied magnetic fields. Figure 6 This is a graph showing the relationship between the magnetic entropy of CeBr3 single crystal and temperature under critical magnetic field (0.2 T) and above critical magnetic field (3 T). Detailed Implementation

[0033] The following are specific embodiments of the present invention, and the technical solutions of the present invention will be further described in conjunction with the embodiments, but the present invention is not limited to these embodiments.

[0034] Unless otherwise specified, the reagents, methods and equipment used in this invention are all conventional reagents, methods and equipment in this technical field.

[0035] The CeBr3 single crystal used in this embodiment of the invention was prepared by the following method: 1. Anhydrous cerium bromide powder with a purity of 99.99% was selected as the raw material. Given the extremely strong hygroscopic nature of CeBr3, all weighing and filling operations were carried out in a glove box filled with high-purity argon gas (H2O < 0.01 ppm, O2 < 0.01 ppm). The raw material was then loaded into strictly cleaned and dried pointed-bottom quartz ampoules, with the ampoule inner diameter selected as 25.4 mm (i.e., 1 inch) according to design requirements.

[0036] 2. To ensure the crystals are free of water of crystallization and oxygen impurities, the quartz ampoules containing the raw materials undergo dynamic vacuum drying before sealing. The ampoules are connected to a high vacuum system, and vacuum is applied at 200-300°C until the background pressure is below 1×10⁻⁶. 4 Pa, for several hours to thoroughly remove trace amounts of moisture and volatile impurities adsorbed on the surface of the raw materials, and then melt and seal the quartz ampoule under vacuum using an oxyhydrogen flame.

[0037] 3. Place the sealed ampoule in a vertical Bridgman growth furnace. The furnace is equipped with a high-temperature zone and a low-temperature zone. The high-temperature zone is set at 760℃ (slightly higher than the melting point of CeBr3, 722℃) to ensure complete melting of the raw materials; the low-temperature zone is set at approximately 600℃. An adiabatic zone with a suitable gradient (gradient of approximately 10-20℃ / cm) is established between the two temperature zones. The ampoule is first kept at a constant temperature in the high-temperature zone for 12-24 hours to homogenize the melt composition and eliminate air bubbles. Subsequently, the descent mechanism is activated, allowing the ampoule to pass through the temperature gradient zone at a speed of 0.5 mm / h to 2.0 mm / h. As the tip of the ampoule enters the low-temperature zone first, crystal nuclei spontaneously form at the tip, guiding the melt to crystallize directionally from bottom to top, growing a single crystal.

[0038] 4. After crystal growth is complete, in order to release the thermal stress generated during growth and prevent crystal cracking, keep the ampoule in the furnace and slowly cool it to room temperature at a rate of 10-20℃ / h. Remove the ampoule and break the quartz tube inside the glove box to remove the crystal rod.

[0039] Sample cutting and orientation: Single crystal blocks of suitable size were cut from the grown crystal rod using a diamond wire cutter. Orientation tests were performed on the samples using a backscatter Laue diffractometer.

[0040] Crystal quality testing: An X-ray beam was incident perpendicularly onto the polished (001) plane of the sample, and the diffraction spot pattern was recorded. The experimentally obtained spot pattern was compared with the theoretically simulated diffraction pattern of CeBr3 crystal in the (001) direction to confirm the single crystallization, crystal quality, and crystal plane orientation deviation of the crystal.

[0041] The result is as follows Figure 1 As shown, the left figure is the Laue diffraction pattern of CeBr3 single crystal in the (001) crystal plane direction; and its corresponding simulated diffraction pattern (right). The clear and significantly symmetrical diffraction spots in the figure are highly consistent with the theoretical crystal structure of CeBr3, indicating that the prepared crystal structure is complete and has good orientation consistency.

[0042] Example 1 1. Experimental Procedure for Measuring Magnetization and Magnetic Anisotropy Sample preparation: Cut a small piece of CeBr3 single crystal sample (usually in the milligram range), weigh it using a precision balance, and confirm the c-axis and a-axis directions of the crystal structure according to the Laue diffraction pattern.

[0043] Measurement instrument: A superconducting quantum interference device (SQUID) was used for magnetic measurement.

[0044] Variable-field magnetization measurement: The sample is fixed on a sample rod, with the applied magnetic field direction parallel to the c-axis of the crystal. The sample temperature is stabilized at set values ​​(2 K, 4 K, 6 K, 8 K, and 10 K). At each temperature point, the applied magnetic field strength is scanned (increasing from 0 T to 7 T), and the curve of the sample's magnetic moment changing with the magnetic field (MB curve) is recorded. The results are as follows: Figure 2 As shown, when an external magnetic field is applied along the c-axis of a CeBr3 single crystal, its magnetization gradually reaches saturation as the magnetic field increases under different temperature conditions.

[0045] Data Fitting: The experimentally measured MB data were converted into magnetization as a function of B / T, and the Brillouin function was used to fit and analyze the magnetization curves at different temperatures to verify its paramagnetic behavior. The results are as follows: Figure 3 As shown, the magnetization data at different temperatures can be well fitted by the Brillouin function, indicating that CeBr3 exhibits typical local paramagnetic behavior in the extremely low temperature region, and the magnetic moment mainly originates from Ce. 3+ The local magnetic moment of an ion.

[0046] Magnetic anisotropy measurement: The sample chamber temperature was kept constant at 2K. First, the magnetization curve was measured when the magnetic field was parallel to the c-axis. Then, the sample was rotated so that the applied magnetic field was parallel to the a-axis of the crystal, and the magnetization curve was measured again at the same temperature. The slopes and saturation behavior of the two curves were compared to characterize the magnetic anisotropy of the material.

[0047] The result is as follows Figure 4 As shown, under 2 K conditions, the magnetization intensity curves of CeBr3 single crystal differ significantly from those of CeBr3 single crystal when an external magnetic field is applied along the c-axis and a-axis, respectively, indicating that the material exhibits significant magnetic anisotropy. Since the magnetic response behavior differs along different crystal axes, the magnetic entropy can be changed simply by altering the orientation of the CeBr3 single crystal relative to the magnetic field, while keeping the applied magnetic field amplitude constant. Based on this characteristic, CeBr3 single crystal is not only suitable for traditional magnetic field-controlled adiabatic demagnetizing refrigeration but can also be further applied to rotating adiabatic demagnetizing refrigeration schemes. This involves achieving a cooling effect by rotating the material or the magnetic field direction, thereby reducing the system temperature without changing the magnetic field strength, reducing the difficulty of magnetic field control and energy consumption, and further enhancing its engineering application potential in cryogenic refrigeration devices.

[0048] 2. Experimental Procedures for Specific Heat Measurement and Magnetic Entropy Calculation Sample preparation: Confirm the c-axis direction of the crystal structure according to the Laue diffraction pattern, cut a small piece of CeBr3 single crystal sample with (001) plane using a wire cutter (the mass is usually around 1 mg), and weigh it using a precision balance.

[0049] Specific heat measurement: The specific heat is measured using the thermal relaxation method with the heat capacity option of the Integrated Physical Property Measurement System (PPMS).

[0050] Sample mounting: The flat CeBr3 single crystal sample with a smooth surface is attached to the thermal capacity sample holder using low-temperature thermal grease (N grease) to ensure good thermal contact.

[0051] Variable-temperature specific heat test: Under an adiabatic high-vacuum environment, external magnetic fields were set to different values ​​such as 0 T, 0.2 T, 1 T, and 3 T. Under each fixed magnetic field, the specific heat of the sample was measured as a function of temperature in the extremely low temperature range (0.07 K to 2 K) and the liquid helium temperature range (2 K to 5 K). C - T curve).

[0052] Magnetic entropy calculation: using thermodynamic relations S ( T , H )=∫ C ( T , H ) / T d T Specific heat data under different magnetic fields ( C / T Integrating the results, we obtain the temperature-entropy curves under different magnetic fields.

[0053] The results of the variable temperature specific heat test are as follows Figure 5 As shown, under different applied magnetic field conditions, the magnetic specific heat of CeBr3 single crystals exhibits significant differences with temperature, indicating that the magnetic field can effectively regulate its low-temperature thermodynamic behavior.

[0054] The results of the temperature-entropy curves under different magnetic fields are as follows: Figure 6 As shown, by comparing the changes in magnetic entropy under critical magnetic fields (approximately 0.2 T) and above critical magnetic fields (e.g., 3 T), the available magnetic entropy of CeBr3 in the low-temperature region can be obtained. The arrows in the figure illustrate a typical adiabatic demagnetization process: after the system is cooled to approximately 1.8 K under a 3 T magnetic field, the system temperature can be further reduced to approximately 45 mK by gradually decreasing the magnetic field strength under near-adiabatic conditions.

[0055] The present invention has been described in detail above with reference to the embodiments of the present invention. However, the present invention is not limited to the above embodiments. Within the scope of knowledge possessed by those skilled in the art, various changes can be made without departing from the spirit of the present invention.

Claims

1. Application of CeBr3 single crystal in adiabatic demagnetizing refrigeration.

2. The application according to claim 1, characterized in that, Application of CeBr3 single crystal in cryogenic thermal insulation and demagnetization refrigeration.

3. The application according to claim 2, characterized in that, The extremely low temperature is ≤100mK.

4. The application according to claim 1, characterized in that, The CeBr3 single crystal is a single crystal with magnetic anisotropy.

5. The application according to claim 1, characterized in that, The application includes achieving cooling by adjusting the magnetic entropy of the CeBr3 single crystal by changing the strength of the applied magnetic field.

6. The application according to claim 1, characterized in that, The application modulates the magnetic entropy by changing the orientation of the CeBr3 single crystal relative to the direction of the applied magnetic field, thereby achieving rotary adiabatic demagnetization refrigeration.

7. The application according to claim 6, characterized in that, The rotating adiabatic demagnetizing cooling process includes: under near-adiabatic conditions and with the applied magnetic field strength remaining constant, the CeBr3 single crystal is changed from the crystal axis direction with a higher degree of magnetization to the crystal axis direction with a lower degree of magnetization relative to the magnetic field direction, thereby increasing the magnetic entropy of the system. Under the condition that the total entropy remains unchanged under adiabatic conditions, the lattice entropy decreases, thereby achieving a temperature drop.

8. The application according to claim 7, characterized in that, The crystal axis direction with higher magnetization is the c-axis direction of the CeBr3 single crystal, and the crystal axis direction with lower magnetization is the a-axis direction of the CeBr3 single crystal.

9. A magnetic refrigeration method based on CeBr3 single crystal, characterized in that, Includes the following steps: Using CeBr3 single crystal as the magnetic working medium, by applying and removing magnetic fields to the magnetic working medium, the temperature of the magnetic working medium changes and heat is transferred with the heat exchanger, thereby achieving the purpose of cooling.

10. A magnetic refrigeration device, characterized in that, The magnetic refrigeration device includes CeBr3 single crystal as the ultra-low temperature magnetic refrigeration medium.

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