Magnetic sensitive wire and manufacturing method thereof

Abstract

Provided is a magneto-sensitive wire suitable for a magnetic sensor that can achieve both an expansion of the measurement range and an improvement in environmental resistance. The magneto-sensitive wire of the present invention comprises a Co-based alloy, and the Co-based alloy comprises Fe. The Co-based alloy comprises more Fe than a reference composition that is amorphous as a whole and has zero magnetostriction. Specifically, in the Co-based alloy, for example, the atomic ratio of the amount of Fe relative to the total amount of the magnetic element group consisting of Co, Fe and Ni, that is, the Fe ratio (Fe / (Co+Fe+Ni)), can be 6.1% to 9.5%. The magneto-sensitive wire is obtained by a heat treatment process, in which the amorphous wire comprising such a Co-based alloy is heated at a specific temperature above the crystallization start temperature and below the crystallization end temperature. As a result, the magneto-sensitive wire becomes a composite structure in which crystal grains are dispersed in an amorphous phase. The magneto-sensitive wire of the present invention has, for example, an anisotropic magnetic field of 5Oe to 70Oe, and a stress sensitivity as an indicator of magnetostriction of ‑30mOe / MPa to 30mOe / MPa.

Description

Technical Field

[0001] The present invention relates to a magnetosensitive wire and the like for a magnetic sensor. Background Art

[0002] Currently, magnetic sensors such as fluxgate sensors (FG sensors), Hall sensors, giant magnetoresistive sensors (GMR sensors), and magneto-impedance sensors (MI sensors) are used. Among these, MI sensors excel in sensitivity, responsiveness, and power consumption compared to other sensors. Therefore, MI sensors are not only used in electronic compasses that measure geomagnetism (approximately 50 μT), but are also being used in a variety of products, including mobile devices such as smartphones, in the automotive and medical fields.

[0003] As devices equipped with MI sensors become more advanced in functionality and their applications expand, MI sensors are required to have a wider measurement range, even in ambient magnetic fields, and higher characteristic stability (environmental resistance) against external environmental fluctuations.

[0004] The MI sensor detects the magnitude of the magnetization rotation generated in the circumferential direction of a magnetosensitive wire (magnetosensitive body) to which a high-frequency or pulsed current is applied, depending on the strength of the surrounding magnetic field, as a change in impedance or voltage. The measurement range of the MI sensor is related to the ease of magnetization rotation within the magnetosensitive wire. The ease of magnetization rotation depends largely on the anisotropic magnetic field (Hk) of the magnetosensitive wire. When the anisotropic magnetic field is small, magnetization rotation is easy to occur, and the measurement range becomes narrower. Conversely, when the anisotropic magnetic field is large, magnetization rotation is difficult to occur, and the measurement range becomes wider.

[0005] Conventional magnetosensitive wires consist of amorphous wires (abbreviated as "amorphous wires"), which are entirely noncrystalline. The anisotropic magnetic field is regulated by the internal stress remaining within the amorphous wires. As the internal stress increases, the anisotropic magnetic field increases, while as the internal stress decreases, the anisotropic magnetic field decreases. Internal stress is imparted through tension annealing (TA), where the amorphous wires are heated while applying tensile stress (tension). The internal stress is regulated by the tension annealing conditions.

[0006] It should be noted that tension annealing is performed by heating the wire in a furnace or by applying electrical current to the wire while tension is applied. In either case, conventional tension annealing is performed with the premise of maintaining the wire in an amorphous state. Specifically, the wire heating temperature (furnace temperature, etc.) is set below the crystallization temperature, or even if the heating temperature is set above the crystallization temperature, crystallization will not occur even after a very short heating time.

[0007] Prior art literature

[0008] Patent Literature

[0009] Patent Document 1: Japanese Patent No. 6428884 Summary of the Invention

[0010] Problems to be solved by the invention

[0011] Patent Document 1 differs from conventional magnetosensitive wires by fundamentally reconsidering tension annealing conditions. The result is a magnetosensitive wire comprising a composite structure consisting of fine grains (also referred to as "crystallites") precipitated within an amorphous phase. These microcrystals increase the anisotropic magnetic field of the magnetosensitive wire, extending the measurement range of the MI sensor.

[0012] Patent Document 1, in its Examples section, cites two Co-based alloys as amorphous wires before heat treatment. These are Co-4.6Fe-11.7Si-11.6B and Co-4.7Fe-10.5Si-10.6B (composition units: atomic %). The atomic ratio of Co to Fe (Fe / Co) is 5.9% to 6%. These Co-based alloys are designed so that when the alloy is entirely amorphous, the magnetostriction is essentially zero (referred to as "zero magnetostriction"). However, since magnetostriction is sensitive not only to the alloy composition but also to the alloy structure, the Co-based alloy that has been subjected to tension annealing to precipitate microcrystals can no longer achieve zero magnetostriction.

[0013] Incidentally, Patent Document 1 (

[0042] ) also describes magnetostriction. Specifically, it states that magnetostriction can be controlled by alloy composition and heat treatment conditions, and that the composition of the amorphous phase (excluding the composition of the grains) has a greater influence than the overall composition. However, Patent Document 1 only specifically describes the control of the anisotropic magnetic field, and does not specifically describe the control of magnetostriction.

[0014] The present invention has been made in view of the above circumstances, and an object of the present invention is to provide a magnetosensitive wire and the like in which anisotropic magnetic field and magnetostriction are adjusted.

[0015] Means used to solve problems

[0016] The present inventors conducted intensive research to address this issue and, by using a wire containing a Co-based alloy containing a higher amount of Fe than the baseline composition for achieving zero magnetostriction, successfully obtained a magnetosensitive wire with an anisotropic magnetic field and magnetostriction within the desired ranges. This development led to the completion of the present invention described below.

[0017] Magnetic Sensitive Line

[0018] (1) The present invention provides a magneto-sensitive wire comprising a Co-based alloy containing Fe, wherein the Co-based alloy contains more Fe than a reference composition that is entirely amorphous and has zero magnetostriction, and comprises a composite structure in which crystal grains are dispersed in an amorphous phase.

[0019] (2) The magnetosensitive wire of the present invention can simultaneously maintain magnetostriction near zero while increasing the anisotropic magnetic field (Hk). By increasing the anisotropic magnetic field, the measurement range of the magnetic sensor using the magnetosensitive wire can be expanded. By controlling magnetostriction, the environmental resistance of the magnetic sensor is ensured.

[0020] Incidentally, one example of a magnetic sensor's environmental performance is the temperature dependence of its sensitivity. Specifically, when the temperature around the magnetic sensor fluctuates, thermal stress may act on the magnetosensitive wire, which is secured by resin or other materials. If the magnetostriction of the magnetosensitive wire is large, this thermal stress may alter the magnetic properties of the wire, potentially changing the sensitivity of the magnetic sensor. Conversely, if the magnetostriction of the magnetosensitive wire remains within a predetermined range near zero, the magnetic sensor can maintain its desired performance despite changes in the environment (e.g., temperature).

[0021] It should be noted that the magnetosensitive wire of the present invention increases its anisotropic magnetic field not only through residual internal stress but also through the formation (precipitation) of fine crystalline phases (grains) within the amorphous phase. This resulting anisotropic magnetic field is stable even in high-temperature environments. Therefore, using the magnetosensitive wire of the present invention ensures that the measurement range of the magnetic sensor is stable even against environmental fluctuations (such as temperature changes).

[0022] Method for manufacturing magnetic sensitive wire

[0023] (1) The present invention can also be understood as a method for producing a magneto-sensitive wire. For example, as described above, the present invention can also be a method for producing the magneto-sensitive wire, comprising a heat treatment step in which an amorphous wire comprising a Co-based alloy containing a higher amount of Fe than in a reference composition is heated at a specific temperature that is above the crystallization start temperature and below the crystallization end temperature. The heat treatment step is performed, for example, by a tension annealing step performed while applying tensile stress to the amorphous wire.

[0024] (2) When an amorphous wire containing more Fe than an alloy composition that achieves zero magnetostriction is heated at a temperature equal to or higher than the crystallization start temperature for a predetermined time, a magnetosensitive wire can be obtained in which fine crystal grains (crystals) having Fe as nuclei are precipitated in the amorphous phase.

[0025] Crystallites prevent spin magnetization rotation (particularly circumferential rotation). Crystallites (crystalline phase) have a higher density than the amorphous phase, and this density difference creates internal stress (compressive stress) in the amorphous phase in the contraction direction. This increases the anisotropic magnetic field of the magnetosensitive wire.

[0026] Furthermore, the magnetostriction of magnetic materials varies sensitively with their structure (composition and organization). Within the amorphous phase, Fe contributes to positive magnetostriction, while Co (and subsequently Ni) contributes to negative magnetostriction. Within the amorphous phase, the positive and negative magnetostriction values, as well as the absolute value of the magnetostriction, are largely determined by the compositional ratio of Fe, Co, and Ni (the magnetic element group).

[0027] When crystal grains with Fe as their nuclei precipitate from the amorphous phase, the Fe content (concentration) in the amorphous phase decreases. As a result, the magnetostriction of the amorphous Co-based alloy (referred to as "magnetostriction of the magnetosensitive wire"), a soft magnetic material, can shift from positive to negative, for example, regardless of the sign and absolute value. Therefore, by adjusting the Fe content and heat treatment conditions, the magnetostriction of the magnetosensitive wire can be brought close to zero magnetostriction.

[0028] As described above, the magnetostriction of the magnetosensitive wire may change with the increase of the anisotropic magnetic field caused by the precipitation of crystal grains, but its form varies depending on the Fe content (Fe ratio). Specifically, within a relatively small range of anisotropic magnetic fields, the magnetostriction of the magnetosensitive wire tends to decrease from the positive side to the negative side. However, within a relatively large range of anisotropic magnetic fields, the magnetostriction of the magnetosensitive wire tends to be roughly constant (saturated) or to increase from the negative side to the positive side. This tendency is believed to be the effect of the precipitation of microcrystals and the structural relaxation of the amorphous phase, depending on the Fe content and heat treatment conditions.

[0029] Note that, since the crystallization start and end temperatures of the amorphous wires may vary depending on the Fe ratio, the specific temperature can be adjusted according to the Fe ratio.

[0030] Components / Sensors

[0031] The present invention can also be understood as an element or sensor using the aforementioned magnetosensitive wire. For example, the present invention can be understood as a magneto-impedance element (MI element) having a magneto-sensitive wire and a detection coil wound around it, or a magneto-impedance sensor (MI sensor) having the MI element.

[0032] "other"

[0033] (1) The "magnetically sensitive wire" of the present invention comprises a composite structure in which crystal grains are dispersed within an amorphous phase. These crystal grains may include crystal grains that do not have Fe as their core. Even for crystal grains with Fe as their core, there are no restrictions on the Fe form (compound, solid solution, etc.) or Fe concentration.

[0034] (2) Magnetostriction (magnetic strain) is a phenomenon in which the shape of a structure changes (strain) due to the application of a magnetic field. In this specification, the term "zero magnetostriction" means that the absolute value of the saturation magnetostriction (magnetostriction constant / λs) is 10 -6 The following situation.

[0035] Magnetostriction is divided into positive magnetostriction (magnetostriction coefficient > 0) and negative magnetostriction (magnetostriction coefficient < 0), with zero magnetostriction as the boundary. Positive magnetostriction means that the magnetic material (magnetosensitive body, wire) expands when a magnetic field is applied, while negative magnetostriction means that the magnetic material contracts when a magnetic field is applied.

[0036] The general measurement of magnetostriction is carried out by measuring the dimensional change of the sample when a magnetic field is applied using a strain gauge directly mounted on the sample. However, it is difficult to directly measure the magnetostriction of extremely fine soft magnetic wires. Therefore, stress sensitivity can be used as an alternative indicator of magnetostriction. Stress sensitivity is the ratio of change in magnetic properties to the stress applied to the magnetic material. Specifically, stress sensitivity is defined as the rate of change (slope) of the anisotropic magnetic field (Hk) relative to the tensile stress applied in the length direction of the wire.

[0037] The relationship between stress sensitivity and magnetostriction is schematically shown in Figure 3 .from Figure 3 It can be seen that the stress sensitivity is negative when the magnetostriction is positive (λs>0), and positive when the magnetostriction is negative (λs<0). When the stress sensitivity is within ±10mOe / MPa (when its absolute value is less than 10mOe / MPa), it can be considered to be zero magnetostriction as described above.

[0038] (3) The reference composition is the alloy composition when the Co-based alloy is entirely amorphous and exhibits zero magnetostriction. As mentioned above, the positive or negative magnetostriction is determined by the composition ratio of the magnetic elements (Fe, Co, and Ni). Specifically, zero magnetostriction is achieved when the Fe ratio (=Fe / (Co+Fe+Ni)) is 5.9% to 6%.

[0039] The increase in the amount of Fe relative to the baseline composition is adjusted by adjusting the amount of other elements relative to the baseline composition. For example, if the adjustment is made within the magnetic element group (Co, Fe, Ni), the increase in Fe is adjusted in the form of a decrease in Co and / or Ni based on the baseline composition. It should be noted that, unless otherwise specified, the alloy composition referred to in this specification is the atomic ratio (atomic %). In addition, in this specification, the case where the Fe composition is greater than the baseline composition or the Fe concentration in the grains is greater than that in the parent phase (amorphous phase) is appropriately referred to as "Fe-rich".

[0040] (4) The term "crystal grains" as used herein is generally very fine, at least within a size that can be observed using a transmission electron microscope (TEM). The particle size (maximum length observed in a TEM image) is, for example, approximately 1 nm to approximately 100 nm, approximately 5 nm to approximately 70 nm, or even approximately 10 nm to approximately 50 nm.

[0041] In addition, the "amorphous (phase)" referred to in this specification may be an amorphous state at least to the extent that crystals cannot be observed by TEM.

[0042] (5) The "crystallization start temperature" and "crystallization end temperature" referred to in this specification are determined as the first (exothermic) peak temperature (Tx1: primary crystallization temperature) and the next (exothermic) peak temperature (Tx2: secondary crystallization temperature), respectively, that appear when differential scanning calorimetry (DSC) is performed on the amorphous line. The crystallization start temperature is generally the temperature at which crystal grains begin to appear (precipitate) from the amorphous phase. The crystallization end temperature is generally the temperature at which the entire amorphous phase crystallizes and the formation of crystal grains ceases.

[0043] (6) Unless otherwise specified, the term "x to y" used in this specification includes the lower limit x and the upper limit y. A range such as "a to b" can be newly set by using any numerical value described in this specification or any numerical value included in the numerical range as a new lower limit or upper limit. Furthermore, unless otherwise specified, the term "x to y nm" used in this specification refers to x nm to y nm. This also applies to other unit systems (e.g., mOe / MPa). BRIEF DESCRIPTION OF THE DRAWINGS

[0044] Figure 1A Graph showing the relationship between the anisotropic magnetic field (Hk) and stress sensitivity for various Fe ratios of the magnetosensitive wire.

[0045] Figure 1B Graph showing the relationship between Fe ratio and stress sensitivity for each Hk.

[0046] Figure 1C This is a bright field (BF) image obtained by observing a cross section of a magnetosensitive wire having an Fe ratio of 8.2% using a high-resolution transmission electron microscope (HR-TEM).

[0047] Figure 1D This is a distribution map of magnetic element concentrations obtained by analyzing the periphery of a microcrystal using a three-dimensional atom probe.

[0048] Figure 2 This is a table showing the relationship between the stress sensitivity of a magneto-sensitive wire and the sensitivity change rate of an MI sensor using the magneto-sensitive wire.

[0049] Figure 3 Schematic diagram showing the relationship between magnetostriction (λs) and stress sensitivity. DETAILED DESCRIPTION

[0050] The components of the present invention described above may be supplemented with one or more components arbitrarily selected from this specification. The contents described in this specification apply not only to the magnetic sensitive wire of the present invention but also to its manufacturing method, etc. Even components related to the method can become components related to the object.

[0051] Co-based alloys

[0052] (1) A Co-based alloy contains Co and an alloying element (group) and can constitute an amorphous soft magnetic alloy. First, the Co-based alloy as a main component (balance) is, for example, greater than 50 atomic %, greater than 60 atomic %, greater than 65 atomic %, or greater than 70 atomic %, relative to the entire Co-based alloy. More specifically, the Co content can be less than 85 atomic %, less than 80 atomic %, or less than 75 atomic %, relative to the entire Co-based alloy.

[0053] Alloy compositions referred to in this specification are expressed in atomic ratios (atomic ratio / stoichiometric ratio) unless otherwise specified. The alloy composition includes ratios relative to the total Co-based alloy (100 atomic %) and ratios relative to the total amount of the magnetic element group (Co + Fe + Ni) (100 atomic %). Unless otherwise specified, the ratio is expressed in terms of ratio relative to the total Co-based alloy (100 atomic %).

[0054] Fe is an essential element for Co-based alloys, but Ni is not. The "total amount of the magnetic element group" referred to in this specification refers to the total amount of Co and Fe, or the total amount of Co, Fe, and Ni. Throughout this specification, the total amount of the magnetic element group is appropriately expressed as "Co + Fe + Ni," regardless of the presence or absence of Ni.

[0055] The total amount of the magnetic element group relative to the entire Co-based alloy is, for example, 65 to 85 atomic %, 70 to 80 atomic %, or 72 to 78 atomic %.

[0056] When Ni is contained, the Ni content is, for example, 0.1 to 3.5 atomic%, 1 to 3 atomic%, or 1.5 to 2.5 atomic% relative to the total amount of the magnetic element group (100 atomic%). When Ni is contained relative to the entire Co-based alloy (100 atomic%), the Ni content is, for example, 0.1 to 2.7 atomic%, 0.7 to 2.3 atomic%, or 1.2 to 1.8 atomic%, depending on the ratio of the magnetic element group to the entire Co-based alloy.

[0057] (2) For example, the amount of Fe relative to the total amount of the magnetic element group (100 atomic %) may be 6.1 atomic % to 9.5 atomic %, 7 atomic % to 9 atomic %, 7.5 atomic % to 8.8 atomic %, or even 8 atomic % to 8.5 atomic %. In this specification, the atomic ratio of Fe relative to the total amount of the magnetic element group [Fe / (Co+Fe+Ni)] is specifically referred to as the "Fe ratio," and the atomic ratio is simply expressed as a percentage (%). Incidentally, when relative to the entire Co-based alloy (100 atomic %), the amount of Fe relative to the entire Co-based alloy may be 4.5 atomic % to 7.2 atomic %, 5.2 atomic % to 6.8 atomic %, 5.6 atomic % to 6.6 atomic %, or even 6 atomic % to 6.4 atomic %. This depends on the ratio of the magnetic element group relative to the entire Co-based alloy.

[0058] It should be noted that Fe becomes the nucleus for the formation of crystal grains that emerge (precipitate) from the amorphous phase. Fe has a tendency to slightly increase the crystallization start temperature and slightly narrow the specific temperature range (crystallization start temperature to crystallization end temperature). When Fe is too little, the amount of precipitation of microcrystals is reduced, and the effect of increasing the anisotropic magnetic field cannot be fully obtained. When Fe is too much, the Co-based alloy as a whole becomes easy to crystallize, resulting in an increase in coercive force. In addition, the magnetostriction of the magnetosensitive wire becomes stable on the positive side.

[0059] (3) The Co-based alloy may contain Si and / or B. Light elements Si and B may contribute to the amorphization of the Co-based alloy and the formation of grains. When they are excessive, the anisotropic magnetic field tends to change rapidly with respect to the treatment temperature.

[0060] The total amount of light elements Si and B (Si+B) may be, for example, 15 to 33 atomic%, 20 to 28 atomic%, or 22 to 26 atomic% relative to the entire Co-based alloy. Alternatively, only one of Si and B may be included. When both Si and B are included, the amount of one of Si and B relative to the total amount of Si and B (100 atomic%) may be 30 to 70 atomic%, 40 to 60 atomic%, or 45 to 55 atomic%.

[0061] (4) The Co-based alloy may further contain Mo, Nb, Zr, W, Cr, Ti, V, etc. These elements may contribute to the amorphization of the Co-based alloy. For example, the total amount of these elements may be 0.5 atomic % to 4 atomic %, or even 1 atomic % to 3 atomic %, relative to the total amount of the Co-based alloy. For example, the amount of Mo alone may be 0.1 atomic % to 2.3 atomic %, or even 0.8 atomic % to 1.8 atomic %, relative to the total amount of the Co-based alloy.

[0062] Composite Organization

[0063] When a wire composed entirely of an amorphous phase (amorphous wire) is subjected to an appropriate heat treatment (such as tension annealing), a magnetically sensitive wire having a composite structure consisting of crystal grains dispersed in the amorphous phase is obtained. The crystal grains are fine, and as described above, they are observed using a TEM. The arithmetic mean (average diameter) of the grain size (maximum length) of each crystal grain observed within the field of view is, for example, 1 nm to 150 nm, 5 nm to 70 nm, and further 10 nm to 50 nm. It should be noted that the coarsening of the crystal grains leads to an increase in coercivity (increase in hysteresis), etc.

[0064] The particle number density of the crystal grains in the composite structure is, for example, 5.5 to 10 (×10 -6 / nm 3 ), and further 6 to 9 (×10 -6 / nm 3 If the particle number density is too low, a sufficient anisotropic magnetic field cannot be obtained. Excessive particle number density can lead to decreased sensitivity of the magnetic sensor and increased hysteresis. The particle number density can also be determined by image processing of the observed image using the analysis software included with the TEM.

[0065] Manufacturing Method

[0066] (1) Amorphous wire

[0067] Amorphous wires can be produced by various methods. Representative methods include the modified Taylor method (see, for example, WO 93 / 5904 / Japanese Patent Publication No. 8-503891) and the rotary liquid spinning method (see, for example, Japanese Patent Application Laid-Open No. 57-79052). Prior to the heat treatment step, the amorphous wire is appropriately drawn to the desired wire diameter.

[0068] (2) Heat treatment process

[0069] A magnetosensitive wire containing a composite structure can be obtained, for example, by heat treating an amorphous wire. The heat treatment temperature (specific temperature: T) can be adjusted between the crystallization start temperature (Tx1) and the crystallization end temperature (Tx2) (Tx1 ≤ T < Tx2) based on the desired anisotropic magnetic field and magnetostriction. When the specific temperature is below Tx1, it is difficult to adjust the anisotropic magnetic field or magnetostriction. When the specific temperature is above Tx2, the coercive force of the magnetosensitive wire increases, or the sensitivity of the magnetic sensor decreases.

[0070] The specific temperature can be set, for example, to a temperature not lower than a first temperature (T1) at which a magnetosensitive wire with an anisotropic magnetic field (Hk) of 5 Oe or 10 Oe is obtained (Tx1 ≤ T1 ≤ T). Alternatively, the specific temperature can be set to a temperature not higher than a second temperature (T2) at which a magnetosensitive wire with an anisotropic magnetic field of 60 Oe or 50 Oe is obtained (T ≤ T2 < Tx2). It should be noted that when heating the amorphous wire in a furnace, the specific temperature (T) is the furnace atmosphere temperature.

[0071] The treatment time also depends on the composition and diameter of the amorphous wire, and is, for example, 0.5 to 15 seconds, 1 to 10 seconds, or 2 to 5 seconds. If the treatment time is too short, the formation of crystal grains may be insufficient, while if it is too long, the grains may grow and coarsen. Heat treatment can be performed in air, an inert gas atmosphere, or a vacuum atmosphere.

[0072] The heat treatment process can be an annealing process performed without applying tensile stress (external stress) to the amorphous wire, or a tension annealing process performed while applying tensile stress to the amorphous wire. During tension annealing (TA), in addition to the internal stress caused by the composite structure, the internal stress caused by the external stress is also additively or synergistically introduced into the magnetosensitive wire. It should be noted that as long as the amorphous wire does not break, the tensile stress can cause not only elastic deformation but also plastic deformation.

[0073] Magnetic Sensitive Line

[0074] By adjusting the Fe ratio and heat treatment conditions, for example, the magnetosensitive wire can exhibit anisotropic magnetic field and magnetostriction (stress sensitivity) that are consistent with the specifications of the magnetic sensor, etc. It should be noted that the magnetostriction can be substantially zero or within a predetermined range that meets the specifications.

[0075] The anisotropic magnetic field is, for example, 5Oe to 70Oe, 10Oe to 60Oe, or 20Oe to 50Oe. Furthermore, the stress sensitivity is, for example, -30mOe / MPa to 30mOe / MPa, -20mOe / MPa to 20mOe / MPa, -10mOe / MPa to 10mOe / MPa, -5mOe / MPa to 5mOe / MPa, or -2mOe / MPa to 2mOe / MPa.

[0076] Magnetic sensitive wires typically have a circular cross-section. The wire diameter ranges from 1 μm to 150 μm, 3 μm to 80 μm, or even 5 μm to 30 μm. If the wire diameter is too small, the sensitivity of the magnetic sensor decreases. If the wire diameter is too large, the cooling rate required to achieve amorphization becomes more stringent.

[0077] "use"

[0078] The magnetosensitive wire of the present invention can be used in various magnetic sensors. For example, it is suitable as a magnetosensitive element of an MI sensor with excellent responsiveness, sensitivity, and power consumption, and particularly as a magnetosensitive element of an MI sensor with a wide magnetic field measurement range.

[0079] Example

[0080] Amorphous wires composed of Co-based alloys with varying Fe ratios were heat-treated (tension annealing) to produce multiple magnetosensitive wires. Their magnetic properties (anisotropic magnetic field and stress sensitivity) were measured and their structures observed. Furthermore, the environmental resistance of MI sensors (magnetic sensors) incorporating these magnetosensitive wires was evaluated. The present invention is described in more detail below, citing specific examples.

[0081] [First embodiment]

[0082] Preparation of Samples

[0083] (1) Amorphous wire

[0084] The raw materials were arc-melted and then subjected to a rotary liquid spinning method to produce amorphous wires (wire diameter: approximately 125 μm) composed of Co-based alloys with varying Fe ratios. This amorphous wire was drawn and cleaned to obtain an amorphous wire with a wire diameter of 18 μm. Drawing was performed using a HSS-21 wire drawing machine manufactured by Saikawa Corporation. Cleaning was performed using ethanol.

[0085] The alloy composition of the Co-based alloy was set to one of the following reference composition examples or a composition in which only the Fe and Co contents were different from the reference composition example. For each Co-based alloy, the contents of Ni, Si, B, and Mo, as well as the total amount of the magnetic element group (Co+Fe+Ni) (75.2 atomic %) were set constant relative to the entire alloy.

[0086] Benchmark composition:

[0087] (atom%)

[0088] The Fe content varies within the range of 5.9 atomic % to 9.2 atomic % relative to the total amount of the magnetic element group (Co + Fe + Ni) (100 atomic %). Incidentally, if the Fe content is relative to the entire Co-based alloy, the Fe content is 4.4 atomic % to 6.9 atomic %. Thus, a plurality of amorphous wires composed of Co-based alloys with different Fe ratios within the range of 5.9% to 9.2% were prepared. The Fe ratio of the Co-based alloy of the above-mentioned reference composition is 5.9%. Incidentally, confirmation by X-ray diffraction showed that the structure of each wire was amorphous (phase) as a whole.

[0089] (2) Heat treatment process

[0090] The wires were wound while being tensioned and passed through a heating furnace placed midway, whereby each wire was subjected to continuous heat treatment (tension annealing). The treatment conditions at this time were as follows.

[0091] The applied tensile stress σ was set to 150 MPa, the passage time in the heating furnace (furnace time) was 3 seconds, the passage length in the heating furnace was 0.52 m, and the treatment atmosphere was set to air. The atmosphere temperature in the heating furnace (treatment temperature / specific temperature) was varied within the range of 500°C to 580°C for each wire with different Fe ratios.

[0092] Determination

[0093] (1) Anisotropic magnetic field

[0094] The anisotropic magnetic field (Hk) of each line was measured for different alloy compositions (Fe ratios) and heat treatment conditions (treatment temperatures) using a vibrating sample magnetometer (PV-M10-5, manufactured by Toei Kagaku Sangyo Co., Ltd.).

[0095] (2) Stress sensitivity

[0096] For each wire, stress sensitivity, an indicator of magnetostriction, was measured. Specifically, a load-variable dancer roller equipped with a strain gauge load cell applied stress (0 MPa to 300 MPa) in the longitudinal direction of the wire while simultaneously applying a magnetic field (0 Oe to 50 Oe) in the same direction. The resulting inductance change in the wire was measured using an LCR meter. This inductance was converted into an anisotropic magnetic field to determine the stress sensitivity of each wire.

[0097] The wire (magnetic sensitive wire) obtained by heat treating the amorphous wire in this way is Figure 1A and Figure 1B The relationship among Fe ratio, anisotropic magnetic field and stress sensitivity is summarized in FIG.

[0098] "observe"

[0099] (1) The cross section of each wire after heat treatment was observed using a high-resolution transmission electron microscope (HR-TEM: manufactured by JEOL Ltd., JEM-2100F). As an example, a TEM image (BF image) of a wire having an Fe ratio of 8.2%, an anisotropic magnetic field of 39 Oe, and a stress sensitivity of 9 mOe / MPa is shown in FIG. Figure 1C The granular black and white dots observed in the TEM image represent crystallites. The difference in color (black and white) in the TEM image represents the difference in crystal orientation.

[0100] (2) For the amorphous line composed of the reference composition (Fe ratio 5.9%), the results of a separate differential scanning calorimetry (DSC) measurement revealed that its crystallization start temperature (Tx1) was 514°C and its crystallization end temperature (Tx2) was 553°C. Amorphous lines with a higher Fe ratio than the reference composition tend to have slightly higher crystallization start temperatures and a slightly narrower temperature range (crystallization start temperature to crystallization end temperature) depending on the Fe ratio. For example, at an Fe ratio of 9.2%, the crystallization start temperature (Tx1) was 517°C and the crystallization end temperature (Tx2) was 548°C.

[0101] "evaluate"

[0102] (1) Anisotropic magnetic field and stress sensitivity (magnetostriction)

[0103] Depend on Figure 1A and Figure 1B It is clear that by adjusting the Fe ratio and heat treatment conditions, the anisotropic magnetic field and stress sensitivity of the magnetosensitive wire can be adjusted over a wide range. Specifically, for example, the anisotropic magnetic field can be adjusted within a range of 5Oe to 60Oe, and further within a range of 10Oe to 55Oe, while keeping the magnetostriction near zero.

[0104] It should be noted that, from Figure 1AIt is also clear that when amorphous wires having an Fe ratio greater than the reference composition (Fe ratio of 5.9%) are heat treated, the stress sensitivity (magnetostriction) tends to converge to approximately zero within a relatively large anisotropic magnetic field range (for example, greater than 35 Oe, and further greater than 40 Oe).

[0105] Furthermore, when an amorphous wire having an Fe ratio within a predetermined range (e.g., an Fe ratio of 7.5% to 8.5%) is heat-treated, there is a point where the stress sensitivity (magnetostriction) is substantially zero (a point where the magnetostriction changes from positive to negative) within a relatively small anisotropic magnetic field range (e.g., 35 Oe or less, and further, 25 Oe or less).

[0106] (2) Composite tissue

[0107] like Figure 1C As shown in FIG, the TEM image obtained by observing the wire after heat treatment also confirmed that a composite structure was obtained, in which a large number of fine grains appeared in the amorphous phase in a roughly uniform manner. The size of the grains (maximum length) was only about 50nm at most, which was very fine. Figure 1D As shown, it was confirmed that Fe was contained in the crystal grains using a three-dimensional atom probe (LEAP4000XSi manufactured by AMTEK).

[0108] [Second embodiment]

[0109] (1)MI sensor

[0110] MI sensors equipped with the above-mentioned magnetic sensitive wires were fabricated. Six types of magnetic sensitive wires with stress sensitivities ranging from 0mOe / MPa to 100mOe / MPa were prepared by adjusting the Fe ratio and heat treatment conditions of the magnetic sensitive wires (refer to Figure 2 ).

[0111] Each MI sensor was produced based on the specifications described in Japanese Patent No. 4650591 or the specification of AMI 306 (commercial product) manufactured by Aichi Steel, Ltd.

[0112] (2) Environmental testing

[0113] Each MI sensor was subjected to an environmental test. The environmental test was conducted by placing the MI sensor in a treatment chamber at a temperature of 80°C and a humidity of 85% and maintaining it for 100 hours. The sensitivity of each MI sensor was measured before and after the high temperature and high humidity test. For each MI sensor (magnetic sensitive wire), the sensitivity change rate was calculated by dividing the sensitivity difference before and after the test by the sensitivity before the test. The stress sensitivity of the magnetic sensitive wire and the sensitivity change rate of the MI sensor are listed in the table below. Figure 2 .

[0114] (3) Evaluation

[0115] from Figure 2 It is clear that by using magnetosensitive wire with low stress sensitivity (magnetostriction), the sensitivity change rate of the MI sensor can be suppressed even under environmental fluctuations. Specifically, for example, if the stress sensitivity of the magnetosensitive wire is within the range of ±30mOe / MPa, the sensitivity drop of the MI sensor can be less than 3%. It should be noted that as environmental tests, gas-phase temperature cycle tests or liquid-phase thermal shock tests can also be performed instead of the above-mentioned high-temperature and high-humidity test. In either case, the same results can be obtained.

[0116] As can be seen from the above, the magnetosensitive wire of the present invention achieves the desired anisotropic magnetic field and magnetostriction (stress sensitivity). In addition, the use of this magnetosensitive wire can provide a magnetic sensor that achieves both an expanded measurement range and improved environmental resistance.

Claims

1. A magnetically sensitive wire, wherein: The magneto-sensitive wire comprises a Co-based alloy, wherein the Co-based alloy comprises Fe, The Co-based alloy contains more Fe than a reference composition that is entirely amorphous and has zero magnetostriction, wherein the Fe content in the Co-based alloy is 7% to 9.5% in atomic ratio relative to the total amount of a magnetic element group consisting of Co, Fe, and Ni, and includes a composite structure in which crystal grains are dispersed in an amorphous phase. The Co-based alloy contains more than 50 atomic % of Co relative to the entirety of the Co-based alloy. The Co-based alloy contains 65 atomic % to 85 atomic % of the magnetic element group in total relative to the entire Co-based alloy. The Co-based alloy further contains Si and / or B in an amount of 15 to 33 atomic % in total relative to the entire Co-based alloy. The Co-based alloy further comprises a total of 0.5 atomic % to 4 atomic % of one or more selected from the group consisting of Mo, Nb, Zr, W, Cr, Ti, and V, or 0.1 atomic % to 2.3 atomic % of Mo, relative to the entire Co-based alloy. The Fe ratio of the reference composition is 5.9% to 6%.

2. The magnetic sensitive wire according to claim 1, wherein The Fe ratio is 7.5% to 9%.

3. The magnetic sensitive wire according to any one of claims 1 or 2, wherein: The Co-based alloy contains 0.1 atomic % to 3.5 atomic % of Ni based on the total amount of the magnetic element group.

4. The magneto-sensitive wire according to claim 1 or 2, wherein: The anisotropy magnetic field is 5Oe to 70Oe and the stress sensitivity is -30mOe / MPa to 30mOe / MPa.

5. A manufacturing method for obtaining the magneto-sensitive wire according to any one of claims 1 to 4, wherein: The manufacturing method includes a heat treatment step of heating an amorphous wire composed of a Co-based alloy containing more Fe than a reference composition that is entirely amorphous and has zero magnetostriction at a specific temperature that is higher than a crystallization start temperature and lower than a crystallization end temperature.

6. The manufacturing method according to claim 5, wherein: The heat treatment step is a tension annealing step performed while applying a tensile stress to the amorphous wires.

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