MAGNETO-SENSITIVE WIRE FOR MAGNETIC SENSORS AND PRODUCTION METHOD THEREFOR

Abstract

An object is to provide a magneto-sensitive wire that exhibits a stable anisotropic magnetic field even under a high-temperature environment and can achieve expansion of the measurement range of an MI sensor, etc. The present invention provides a magneto-sensitive wire for magnetic sensors that comprises a Co-based alloy having a composite structure in which crystal grains are dispersed in an amorphous phase. The Co-based alloy contains 0.05 to 0.80 at %, preferably 0.10 to 0.60 at %, of Cu with respect to 100 at % of the Co-based alloy as a whole. The Co-based alloy may further contain 65 to 90 at % of the group of magnetic elements consisting of Co, Fe, and Ni as the total, 15 to 27 at % of Si and/or B as the total, and 0.5 to 2.5 at % of Mo. Such a magneto-sensitive wire is excellent in the heat resistance and exhibits a stable anisotropic magnetic field even under a high-temperature environment. By using the magneto-sensitive wire of the present invention, it is possible, for example, to efficiently produce an MI sensor with an expanded measurement range.

Claims

1. A magneto-sensitive wire for magnetic sensors, comprising a Co-based alloy having an amorphous phase, the Co-based alloy containing 0.05 to 0.80 at % of Cu with respect to 100 at % of the Co-based alloy as a whole and having a composite structure in which crystal grains are dispersed in the amorphous phase.

2. The magneto-sensitive wire for magnetic sensors according to claim 1, wherein at least a part of the crystal grains contains Cu.

3. The magneto-sensitive wire for magnetic sensors according to claim 1, wherein the Co-based alloy contains 60 at % or more of Co with respect to the Co-based alloy as a whole.

4. The magneto-sensitive wire for magnetic sensors according to claim 3, wherein the Co-based alloy contains 65 to 90 at % of a group of magnetic elements consisting of Co, Fe, and Ni as a total with respect to the Co-based alloy as a whole.

5. The magneto-sensitive wire for magnetic sensors according to claim 4, wherein the Fe is contained in an amount of 2.5 to 12 at % with respect to a total amount of the group of magnetic elements as a whole.

6. The magneto-sensitive wire for magnetic sensors according to claim 4, wherein the Ni is contained in an amount of 1 to 3 at % with respect to a total amount of the group of magnetic elements as a whole.

7. The magneto-sensitive wire for magnetic sensors according to claim 4, wherein the Co-based alloy contains 20 to 35 at % of Si and/or B as a total with respect to a total amount of the group of magnetic elements as a whole.

8. The magneto-sensitive wire for magnetic sensors according to claim 1, wherein the Co-based alloy further contains 15 to 27 at % of Si and/or B as a total with respect to the Co-based alloy as a whole.

9. The magneto-sensitive wire for magnetic sensors according to claim 1, wherein the Co-based alloy further contains 0.5 to 2.5 at % of Mo with respect to the Co-based alloy as a whole.

10. A method of producing a magneto-sensitive wire for magnetic sensors, comprising a heat treatment step of heating an amorphous wire comprising a Co-based alloy at a specific temperature equal to or higher than a crystallization start temperature and lower than a crystallization end temperature, the Co-based alloy containing 0.05 to 0.80 at % of Cu, wherein the magneto-sensitive wire for magnetic sensors that comprises a composite structure in which crystal grains are dispersed in an amorphous phase is obtained.

11. The method of producing a magneto-sensitive wire for magnetic sensors according to claim 10, wherein the heat treatment step is a tension annealing step performed while applying tensile stress to the amorphous wire.

12. The method of producing a magneto-sensitive wire for magnetic sensors according to claim 10, wherein the specific temperature is equal to or higher than a first temperature at which the magneto-sensitive wire for magnetic sensors that has an anisotropic magnetic field (Hk) of 10 Oe is obtained.

Description

BRIEF DESCRIPTION OF DRAWINGS

[0026] FIG. 1 is a graph illustrating measurement results of DSC according to a first example.

[0027] FIG. 2 is a set of HR-TEM images when observing cross sections of wires (Cu: 0% and Cu: 0.20%) according to the first example.

EMBODIMENTS FOR CARRYING OUT THE INVENTION

[0028] One or more features freely selected from the present specification can be added to the above-described features of the present invention. The content described in the present specification corresponds not only to the magneto-sensitive wire of the present invention but also to a method of producing the same and relevant techniques, as appropriate. Methodological features can even be features regarding a product.

«Co-Based Alloy»

[0029] (1) The Co-based alloy is composed of Co and plural types of alloy elements in order to constitute an amorphous soft magnetic alloy. First, Co, which is the main component (the balance), is contained, for example, in an amount of more than 50 at % in an embodiment, 60 at % or more in another embodiment, 65 at % or more in still another embodiment, or 70 at % or more in a further embodiment with respect to the Co-based alloy as a whole. Suffice it to say that Co may be contained in an amount of 85 at % or less in an embodiment, 80 at % or less in another embodiment, or 75 at % or less in a further embodiment with respect to the Co-based alloy as a whole.

[0030] Unless otherwise stated, the alloy composition as referred to in the present specification is represented by an atomic ratio (stoichiometric ratio). Representation of the alloy composition includes a ratio to the Co-based alloy as a whole (100 at %) and a ratio to the total amount of the group of magnetic elements (Co+Fe+Ni) as a whole (100 at %). Unless otherwise stated, the ratio to the Co-based alloy as a whole (100 at %) is referred to. Note that Fe or Ni is not necessarily an essential element of the Co-based alloy. Accordingly, when the ratio to the total amount of the group of magnetic elements is referred to, the Co-based alloy may contain Co and Fe, may contain Co and Ni, may contain Co, Fe, and Ni, or may contain only Co.

[0031] (2) The Co-based alloy may contain Fe so that the magneto-sensitive wire (amorphous wire) has zero magnetostriction (e.g., the absolute value of magnetostriction is less than 10.sup.−6) or its vicinity. Fe is contained, for example, in an amount of 2.5 to 12 at % in an embodiment or 3 to 10 at % in another embodiment with respect to the total amount of the group of magnetic elements as a whole. For example, Fe is contained in an amount of 2 to 10 at % in an embodiment or 2.5 to 8 at % in another embodiment with respect to the Co-based alloy as a whole.

[0032] The Co-based alloy may contain Ni in order to be an amorphous soft magnetic alloy. Ni is contained, for example, in an amount of 1 to 3 at % in an embodiment or 1.5 to 2.5 at % in another embodiment with respect to the total amount of the group of magnetic elements as a whole. For example, Ni is contained in an amount of 0.5 to 2.5 at % in an embodiment or 1 to 2 at % in another embodiment with respect to the Co-based alloy as a whole.

[0033] The total amount of the group of magnetic elements consisting of Co, Fe, and Ni is, for example, an amount of 65 to 90 at % in an embodiment or 70 to 85 at % in another embodiment with respect to the Co-based alloy as a whole.

[0034] (3) The Co-based alloy may contain Si and/or B. Si and/or B are contained, for example, in an amount of 20 to 35 at % in an embodiment or 24 to 33 at % in another embodiment as the total (Si+B) with respect to the total amount of the group of magnetic elements as a whole. For example, Si and/or B are contained in an amount of 15 to 27 at % in an embodiment or 18 to 25 at % in another embodiment as the total with respect to the Co-based alloy as a whole. When only one of Si and B is used, it is contained, for example, in an amount of 10 to 20 at % in an embodiment or 12 to 18 at % in another embodiment with respect to the total amount of the group of magnetic elements as a whole. For example, one of Si and B is contained in an amount of 7 to 17 at % in an embodiment or 9 to 15 at % in another embodiment with respect to the Co-based alloy as a whole. Si and B contribute to the formation of an amorphous Co-based alloy and the appearance of crystal grains. Note, however, that if they are excessive, the anisotropic magnetic field tends to change suddenly with respect to the treatment temperature.

[0035] (4) The Co-based alloy may further contain Mo, Cr, Nb, Zr, etc. These elements can also contribute to the formation of an amorphous Co-based alloy. These elements are contained, for example, in an amount of 0.5 to 4 at % in an embodiment or 1 to 3 at % in another embodiment as the total with respect to the Co-based alloy as a whole. When only Mo is used, it may be contained, for example, in an amount of 0.5 to 2.5 at % in an embodiment or 1 to 2 at % in another embodiment with respect to the Co-based alloy as a whole.

[0036] (5) As previously described, Cu promotes lowering the temperature (crystallization start temperature) at which the crystal grains appear from the amorphous phase and widening the temperature range (crystallization start temperature to crystallization end temperature). If the amount of Cu is unduly small, such effects will be poor, while if the amount of Cu is unduly large, the coercive force will increase. Cu is preferably contained, for example, in an amount of 0.05 to 0.80 at % in an embodiment, 0.10 to 0.60 at % in another embodiment, or 0.15 to 0.40 at % in a further embodiment with respect to the Co-based alloy as a whole.

«Composite Structure»

[0037] When a wire (amorphous wire) composed of an amorphous phase as a whole is subjected to heat treatment (such as tension annealing), a magneto-sensitive wire having a composite structure in which crystal grains are dispersed in the amorphous phase is obtained. The crystal grains are fine and are observed by TEM as previously described. The arithmetic average value (average diameter) of the particle diameters (maximum lengths) of crystal grains observed in the field of view is, for example, 1 to 150 nm in an embodiment, 5 to 70 nm in another embodiment, or 10 to 50 nm in a further embodiment. The coarsening of crystal grains causes an increase in the coercive force (increase in the hysteresis) and the like.

[0038] The particle number density of crystal grains in the composite structure is, for example, 5.5 to 10 (×10.sup.−6/nm.sup.3) in an embodiment or 6 to 9 (×10.sup.−6/nm.sup.3) in another embodiment. If the particle number density is unduly low, a sufficient anisotropic magnetic field cannot be obtained. An unduly high particle number density causes a decrease in the sensitivity of the magnetic sensor and an increase in the hysteresis. The particle number density is also obtained by image-processing the observed image using analysis software attached to the TEM.

«Production Method»

(1) Amorphous Wire

[0039] The amorphous wire can be produced through various methods. Examples of typical methods of producing amorphous wires include the modified Tailor method (references: WO93/5904, or Japanese Translation of PCT International Application, No. 8-503891, etc.) and the in-rotating-liquid spinning method (references: JP57-79052A, etc.). The amorphous wire is drawn to a desired wire diameter as appropriate before the heat treatment step.

(2) Heat Treatment Step

[0040] The magneto-sensitive wire having a composite structure is obtained, for example, by heat-treating an amorphous wire. The temperature for the heat treatment (specific temperature: T) may be adjusted between the crystallization start temperature (Tx1) and the crystallization end temperature (Tx2) (Tx1≤T<Tx2) in accordance with the desired anisotropic magnetic field. If the specific temperature is unduly low, the anisotropic magnetic field cannot be increased, while if the specific temperature is unduly high, the coercive force will increase rapidly.

[0041] The specific temperature may also be, for example, equal to or higher than a first temperature (T1) at which the magneto-sensitive wire having an anisotropic magnetic field (Hk) of 10 Oe is obtained (Tx1≤T<T). Additionally or alternatively, the specific temperature may be equal to or lower than a second temperature (T2) at which the magneto-sensitive wire having an anisotropic magnetic field of 40 Oe or 20 Oe is obtained (T≤T2<Tx2). When the amorphous wire is heated in a furnace, the specific temperature (T) is the atmosphere temperature in the furnace.

[0042] Depending on the component composition and wire diameter of the amorphous wire and other factors, the treatment time is, for example, 0.5 to 15 seconds in an embodiment or 1 to 10 seconds in another embodiment. An unduly short time may cause insufficient appearance of the crystal grains, while an unduly long time may cause the crystal grains to readily grow to become coarse. The heat treatment may be performed in an air atmosphere or otherwise in an inert gas atmosphere or a vacuum atmosphere.

[0043] The heat treatment step may be an annealing step performed without applying tensile stress (external stress) to the amorphous wire or may also be a tension annealing step performed while applying tensile stress to the amorphous wire. When the tension annealing (TA) is performed, in addition to the internal stress due to the composite structure, the internal stress due to the external stress is additively or synergistically introduced into the magneto-sensitive wire. The amorphous wire may be not only elastically deformed but also plastically deformed due to the tensile stress, provided that the amorphous wire does not break.

«Magneto-Sensitive Wire»

[0044] The cross section of the magneto-sensitive wire is usually circular. The wire diameter is, for example, 1 to 150 μm in an embodiment, 3 to 80 μm in another embodiment, or 5 to 30 μm in a further embodiment. If the wire diameter is unduly small, the sensitivity of the magnetic sensor will be lowered. If the wire diameter is unduly large, strict management of the cooling rate for forming an amorphous magneto-sensitive wire will be required.

«Application»

[0045] The magneto-sensitive wire of the present invention can be used for various magnetic sensors. The magneto-sensitive wire of the present invention is suitable for the magneto-sensitive body of an MI sensor that is excellent in the responsivity, sensitivity, power consumption, and other properties.

EXAMPLES

[0046] A number of amorphous wires having different alloy compositions were produced, which were used to reveal the relationship between the treatment temperature and the magnetic characteristics. In addition, the metallographic structures of the amorphous wires after the tension annealing were observed. The present invention will be described in more detail below with reference to such specific examples.

First Example

«Making of Samples»

(1) Amorphous Wires

[0047] The raw materials compounded in the alloy composition 1 (unit: at %) listed below were arc-melted to obtain Co-based alloys with different Cu content ratios (x: 0≤x≤1). Using each Co-based alloy, a glass-coated wire was produced by the modified Tailor method. When confirmed with a scanning electron microscope (SEM), the diameter of the core portion (metal portion other than the glass) of each wire was about 11 μm. In addition, when confirmed with an X-ray diffraction method, the entire structure of the core portion was amorphous (phase).

{(Co.sub.89.8Fe.sub.8.2Ni.sub.2).sub.0.762(Si.sub.50B.sub.50).sub.0.238}.sub.(98.7-x)/100Mo.sub.1.3Cu.sub.x.Math.(Co.sub.68.43Fe.sub.6.25Ni.sub.1.52Si.sub.11.9B.sub.11.9).sub.(98.7-x)/100Mo.sub.1.3Cu.sub.x  <Alloy Composition 1>

(2) Heat Treatment Step

[0048] Each wire was subjected to continuous heat treatment (tension annealing) by winding the wire and passing it through a heating furnace provided in mid-course while applying tension to the wire. The treatment conditions at that time were as follows.

[0049] The treatment conditions were set to include the applied tensile stress σ=200 MPa, the passing time in the heating furnace (time in the furnace): 6.7 seconds, the length of the heating furnace to pass through: 0.52 m, and the treatment atmosphere: in the air. The atmosphere temperature (referred to as a “treatment temperature”/specific temperature) in the heating furnace to pass through was variously changed in a range of 500° C. to 600° C.

«Measurement»

(1) Magnetic Characteristics

[0050] For each wire heat-treated at various treatment temperatures, the magnetic characteristics (anisotropic magnetic field: Hk, coercive force: iHc) were measured using a vibrating sample magnetometer (available from Toei Scientific Industrial Co., Ltd., PV-M10-5). Relationships between the amount of Cu (x), the treatment temperature, and the magnetic characteristics are collectively listed in Table 1.

(2) Differential Scanning calorimetry (DSC)

[0051] Differential scanning calorimetry (DSC) was performed on each wire (amorphous wire) before the heat treatment. Some of the measurement results (Cu: 0 at %, 0.20 at %, 1.00 at %) are collectively illustrated in FIG. 1.

«Observation»

[0052] The cross section of each wire after the heat treatment was observed with a high resolution transmission electron microscope (HR-TEM: available from JEOL Ltd., JEM-2100F). Some of the obtained TEM images (BF) (Cu: 0 at %, 0.20 at %/treatment temperature: 580° C.) are shown in FIG. 2.

[0053] On the basis of the obtained TEM images, the average diameter (arithmetic average of the maximum lengths in a plan view) and particle number density of the crystal grains confirmed in the field of view (about 3 μm×2 μm/sample thickness: 0.1 μm) were calculated using the image processing software attached to the HR-TEM.

«Evaluation»

(1) Temperature Range of Crystallization

[0054] As apparent from FIG. 1, all the DSC curves exhibited double peaks. As the Cu content ratio increased, the prior peak (left side in the figure) indicating the crystallization start temperature (T1x) shifted to the lower temperature side. In addition, the interval between the prior peak and the posterior peak (right side in the figure) indicating the crystallization end temperature (Tx2) was expanded. It has therefore been found that when the Co-based alloy contains Cu, the crystallization start temperature (temperature at which crystal grains start to appear from the amorphous phase of the wire) is lowered, and the temperature range (from the crystallization start temperature to the crystallization end temperature) in which the crystal grains can appear is expanded.

(2) Composite Structure

[0055] As apparent from FIG. 2, when the Co-based alloy contained Cu, a composite structure in which a large number of crystal grains appeared was obtained even at the same treatment temperature. When Cu was 0%, the average diameter of the crystal grains was 18 nm and the particle number density was 5.2×10.sup.−6/nm.sup.3. When Cu was 0.20%, the average diameter of the crystal grains was 20 nm and the particle number density was 8.7×10.sup.−6/nm.sup.3. Also from these, it has been revealed that Cu is involved in the appearance of crystal grains.

[0056] It can also be found from FIG. 2 that the crystal grains are very fine with a grain diameter of about 50 nm at the maximum. It has been confirmed by the selected area diffraction that the small dots appearing black or white in FIG. 2 are fine crystal grains. It has also been confirmed that Cu is contained in the crystal grains, by a three-dimensional atom probe (available from AMTEK, LEAP4000XSi).

(3) Anisotropic Magnetic Field

[0057] As apparent from Table 1, it can be found that when the Co-based alloy contains Cu, the same anisotropic magnetic field (Hk) occurs in a lower temperature region than when the Co-based alloy does not contain Cu (Cu: 0 at %).

[0058] It can also be found from Table 1 that when the Co-based alloy contains Cu, the treatment temperature range (temperature difference) corresponding to a predetermined range of the anisotropic magnetic field (e.g., Hk=10 to 40 Oe) is expanded. That is, it can be said that when the Co-based alloy contains Cu, the temperature dependence of the anisotropic magnetic field is moderate.

[0059] Such a tendency occurs regardless of the amount of Cu at least in a range of Cu≤1.00 at % and is consistent with the previously described DSC measurement results. Note, however, that when the amount of Cu is close to 1.00 at % as the content ratio, the treatment temperature range is expanded, but the coercive force is also increased. Therefore the amount of Cu in the Co-based alloy is preferably 0.05 to 0.80 at % and particularly preferably 0.10 to 0.60 at %.

Second Example

«Making of Samples/Measurement»

[0060] The raw materials compounded in the alloy compositions 2 to 4 (unit: at %) listed below were arc-melted to obtain plural types of Co-based alloys with different Cu content ratios (x: 0≤x≤1). As in the case of the first example, each amorphous wire made by the improved Tailor method was subjected to heat treatment (tension annealing) in which the treatment temperature was variously changed. The treatment temperature range was set to 500° C. to 600° C. for the alloy composition 2 and 540° C. to 640° C. for the alloy compositions 3 and 4. The reason why the treatment temperature range was changed in accordance with the alloy composition is that the temperature range in which fine crystals are precipitated differs depending on the content ratios of Si and B in the Co-based alloy.

[0061] As in the first example, the magnetic characteristics of each wire after the heat treatment were measured. Relationships between the Cu content ratio (x), the treatment temperature, and the magnetic characteristics are collectively listed in Table 2 (alloy composition 2), Table 3 (alloy composition 3), and Table 4 (alloy composition 4).

{(Co.sub.92.7Fe.sub.5.3Ni.sub.2).sub.0.8(Si.sub.50B.sub.50).sub.0.2}.sub.(98.5-x)/100Mo.sub.1.5Cu.sub.x.Math.(Co.sub.74.16Fe.sub.4.24Ni.sub.1.6Si.sub.10B.sub.10).sub.(98.5-x)/100Mo.sub.1.5Cu.sub.x  <Alloy Composition 2>

{(Co.sub.94.6Fe.sub.3.4Ni.sub.2).sub.0.765(Si.sub.50B.sub.50).sub.0.235}.sub.(98.5-x)/100Mo.sub.1.5Cu.sub.x.Math.(Co.sub.72.37Fe.sub.2.6Ni.sub.1.53Si.sub.11.75B.sub.11.75).sub.(98.5-x)/100Mo.sub.1.5Cu.sub.x  <Alloy Composition 3>

{(Co.sub.88.2Fe.sub.9.8Ni.sub.2).sub.3.765(Si.sub.50B.sub.50).sub.0.235}.sub.(98.5-x)/100Mo.sub.1.5Cu.sub.x.Math.(Co.sub.67.47Fe.sub.7.5Ni.sub.1.53Si.sub.11.75B.sub.11.75).sub.(98.5-x)/100Mo.sub.1.5Cu.sub.x  <Alloy Composition 4>

«Evaluation»

[0062] As apparent from comparison between Tables 2 to 4 and Table 1, it has been found that the same tendency as in the first example is exhibited even when the alloy composition is changed. That is, it has been found that even when the Co-based alloys have different alloy compositions, Cu is contained thereby to be able to lower the treatment temperature at which a desired anisotropic magnetic field (Hk) is obtained and expand the treatment temperature range in which the anisotropic magnetic field can be adjusted.

[0063] Moreover, the same tendency has been found that even when the alloy composition changes, at a Cu content ratio of 1.00 at %, the treatment temperature range expands while the coercive force also increases rapidly.

[0064] From the above, it has been revealed that according to the magneto-sensitive wire of the present invention, the treatment temperature at which a desired anisotropic magnetic field can be obtained is lowered and its range is widened; therefore, a magneto-sensitive wire having an anisotropic magnetic field corresponding to the measurement range can be stably obtained.

TABLE-US-00001 TABLE 1 Alloy composition 1: {(Co.sub.89.8Fe.sub.8.2Ni.sub.2.0).sub.0.762 (Si.sub.50B.sub.50).sub.0.238 } .sub.(98.7−x)/100 Mo.sub.1.3 Cu.sub.x Cu (at %) Treatment temperature (° C.) 0 0.10 0.20 0.30 0.50 1.00 Hk 10 569 560 552 557 547 540 (Oe) 20 572 566 562 563 555 555 40 577 571 572 573 562 572 Treatment temperature  8  11  20  16  15  32 difference (° C.) when Hk: 10 to 40 (Oe) Coercive force (Oe) 0.7 1.0 0.8 1.1 1.2 6.2 when Hk: 40 (Oe)

TABLE-US-00002 TABLE 2 Alloy composition 2: {(Co.sub.92.7Fe.sub.5.3Ni.sub.2.0).sub.0.8 (Si.sub.50B.sub.50).sub.0.2 } .sub.(98.5−x)/100 Mo.sub.1.5 Cu.sub.x Cu (at %) Treatment temperature (° C.) 0 0.10 0.20 0.30 0.50 1.00 Hk 10 475 465 458 464 455 446 (Oe) 20 481 474 473 474 466 463 40 494 487 489 488 481 488 Treatment temperature  19  22  31  24  26  42 difference (° C.) when Hk: 10 to 40 (Oe) Coercive force (Oe) 0.7 1.0 0.8 1.2 1.4 5.9 when Hk: 40 (Oe)

TABLE-US-00003 TABLE 3 Alloy composition 3: {(Co.sub.94.6Fe.sub.3.4Ni.sub.2.0).sub.0.765 (Si.sub.50B.sub.50).sub.0.235 } .sub.(98.5−x)/100 Mo.sub.1.5 Cu.sub.x Cu (at %) Treatment temperature (° C.) 0 0.10 0.20 0.30 0.50 1.00 Hk 10 593 584 576 578 568 563 (Oe) 20 610 604 603 600 592 592 40 — — — — — — Treatment temperature  17  20  27  22  24  29 difference (° C.) when Hk: 10 to 20 (Oe) Coercive force (Oe) 1.2 1.5 1.2 1.6 1.9 6.2 when Hk: 40 (Oe)

TABLE-US-00004 TABLE 4 Alloy composition 4: {(Co.sub.88.2Fe.sub.9.8Ni.sub.2.0).sub.0.765 (Si.sub.50B.sub.50).sub.0.235 } .sub.(98.5−x)/100 Mo.sub.1.5 Cu.sub.x Cu (at %) Treatment temperature (° C.) 0 0.10 0.20 0.30 0.50 1.00 Hk 10 590 580 572 579 569 559 (Oe) 20 595 588 585 587 577 577 40 600 593 594 594 587 597 Treatment temperature  10  13  22  15  18  38 difference (° C.) when Hk: 10 to 40 (Oe) Coercive force (Oe) 1.0 14 1.1 1.6 1.8 6.3 when Hk: 40 (Oe)