JP2008034815A - SmFeN NANO-COMPOSITE MAGNETIC PARTICLE AND MANUFACTURING METHOD THEREOF - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide SmFeN nanocomposite magnetic particles which represent high magnetic anisotropy as the entire particles, along with its manufacturing method, at a low cost. <P>SOLUTION: By using a discharge plasma sintering method, SmFeN magnetic particles are applied with pulse currents under a pressure, to decompose a part of SmFeN single crystal phase constituting the SmFeN magnetic particle, for Fe crystal phase to be precipitated. Thus, SmFeN nanocomposite magnetic particles of mixed-phase system are obtained in which Fe crystal particles are dispersed as soft magnetic phase in the SmFeN single crystal phase as hard magnetic phase. By electrifying under pressure while the SmFeN magnetic particles are applied with a specified magnetic field, a part of the particles is decomposed while crystal orientation of the SmFeN magnetic particles is maintained in the applied magnetic field. Thus, SmFeN nanocomposite magnetic particles having a magnetic anisotropy equal to or higher than that of the SmFeN magnetic particles having been subjected to decomposition are provided. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention relates to SmFeN nanocomposite magnetic particles and a method for producing the same, and more particularly to what can be a constituent element of an anisotropic SmFeN nanocomposite magnet.

  Nanocomposite magnets as next-generation high-performance magnets have higher magnetic properties than conventional NdFeB magnets due to the exchange interaction between the soft magnetic phase of the nano order and the hard magnetic phase adjacent to the soft magnetic phase. Research and development is underway for practical application.

  As this type of nanocomposite magnet material, an NdFeB-based material having a high magnetic force level is generally used, but in addition to this, it has the same potential as the NdFeB-based material with respect to the magnetic force level, and has heat resistance and corrosion resistance. Is promising, SmFeN-based materials exhibiting properties superior to NdFeB, and various studies have been made for practical application.

As a method for producing these nanocomposite magnet materials, for example, a method described in JP-A-10-261515 is known (see Patent Document 1). This is a method using a so-called single roll method, in which a raw material containing Sm or Fe as an element is melted, and a raw material in a molten state is supplied from a nozzle onto a Cu roll and rapidly cooled. As a result, a quenched foil strip made of an amorphous structure or a structure containing fine crystals in the amorphous structure is obtained. Thereafter, the quenched foil strip is pulverized, and encapsulated and hot-worked to crystallize an SmFe crystal phase and a soft magnetic phase (Fe crystal phase) that become a hard magnetic phase. Finally, gas nitriding is performed to obtain an SmFeN nanocomposite magnetic powder composed of an SmFeN crystal phase and an Fe crystal phase.
Japanese Patent Laid-Open No. 10-261515

  In the nanocomposite magnetic powder (particles) obtained by the above method, it is ideal that the crystal orientations of the soft magnetic phase and the hard magnetic phase are aligned. In the method of crystallizing phases, it is difficult to align the crystal orientation of the hard magnetic phase, and the magnetic grains as a whole do not exhibit sufficient magnetic anisotropy. Further, the above-described method requires a plurality of steps, and an increase in the number of man-hours leads to an increase in cost.

  Therefore, the present invention has a technical problem to provide SmFeN nanocomposite magnetic particles that can exhibit high magnetic anisotropy as a whole particle and a method for producing the same at low cost.

  In order to solve the above-mentioned problems, the present invention provides an SmFeN nanocomposite comprising an SmFeN single crystal phase as a hard magnetic phase and an Fe crystal phase as a soft magnetic phase generated by decomposing a part of the SmFeN single crystal phase. Magnetic particles are provided.

  As described above, the SmFeN nanocomposite magnetic particle according to the present invention has a mixed phase structure in which the SmFeN single crystal phase and the Fe crystal phase generated by decomposition of a part of the SmFeN single crystal phase coexist. The SmFeN single crystal phase forms a hard magnetic phase with a uniform crystal orientation. Accordingly, the SmFeN single crystal phase having a uniform crystal orientation can be left in the hard magnetic phase while the entire particle is made into a nanocomposite by decomposition and formation of the Fe crystal phase. Thereby, the nanocomposite magnetic particle which shows high magnetic anisotropy as the whole particle | grain can be obtained.

  In order to solve the above-mentioned problem, the present invention applies a current while applying pressure to the SmFeN magnetic particles, decomposes a part of the SmFeN single crystal phase forming the SmFeN magnetic particles, and precipitates the Fe crystal phase. The present invention provides a method for producing SmFeN nanocomposite magnetic particles, which obtains magnetic particles having a mixed phase structure in which an Fe crystal phase as a soft magnetic phase is dispersed in an SmFeN single crystal phase as a hard magnetic phase.

  As described above, the method according to the present invention is intended to make the magnet raw material into a nanocomposite by a method different from the conventional method. According to this method, the granular Fe crystal phase to be decomposed and precipitated remains undecomposed. In addition, magnetic particles having a structure in which the SmFeN single crystal phase coexists can be obtained. Therefore, when the method according to the present invention is applied to SmFeN magnetic particles composed of a single crystal phase with a uniform crystal orientation, a hard magnetic phase having the same crystal orientation can be obtained. Therefore, SmFeN nanocomposite magnetic particles exhibiting high magnetic anisotropy as a whole can be obtained, and as a result, production of a nanocomposite magnet that can exhibit high magnetic properties {for example (BH) max} becomes possible.

  In addition, since the nanocomposite magnetic particles can be produced by a simpler method than the conventional method, the production process can be simplified. Thereby, the nanocomposite magnetic particles or a nanocomposite magnet formed of these particles can be manufactured at a lower cost.

  The decomposition of the SmFeN magnetic particles can be performed, for example, by generating discharge plasma between the magnetic particles. Here, as a method for generating discharge plasma, a method called a discharge plasma sintering method (SPS method) is well known. This method activates the particle surface by applying a pulse current to the powder material supplied in a mold formed of a material such as graphite while applying a pulse current and generating discharge plasma between the powder particles. An effective heat treatment is performed on the particles in a short time. In the present invention, it does not matter whether or not a sintering action is produced between the powder particles as a result of the heat treatment performed by the same method. Similarly, the presence or absence of a sintering action is not questioned with respect to other energization treatments to be described later.

  Thus, one feature of the present invention is that the discharge plasma sintering method, which is usually used for powder sintering, is used for the decomposition (in other words, nanocomposite formation) of SmFeN magnetic particles used as magnet raw materials. Is. According to this method, since the decomposition of the SmFeN magnetic particles is performed uniformly, the Fe crystal phase can be dispersed and precipitated in the SmFeN single crystal phase as much as possible. Therefore, SmFeN nanocomposite magnetic particles having a homogeneous crystal structure as a whole can be formed. In addition, since the Fe crystal phase as a soft magnetic phase is dispersed and precipitated in the nano order, a highly magnetic nanocomposite magnet capable of exhibiting better exchange interaction can be obtained.

  As described above, the present invention is characterized in that the SmFeN magnetic particles are decomposed so that the Fe crystal phase as a soft magnetic phase is precipitated in the SmFeN single crystal phase when the SmFeN magnetic particles are pressurized and energized. However, in this case, it is necessary to promote the decomposition reaction partially by optimizing the decomposition conditions so that the SmFeN single crystal phase is not completely decomposed.

  Here, not only the discharge plasma sintering method (SPS method) but also the SmFeN magnetic particles are decomposed by applying a pulse current while applying pressure as in the present invention, the decomposition of the Fe crystal phase is affected. As factors presumed to be, pressure, current amount (energization amount), pulse condition, processing time (energization time), and processing atmosphere can be considered. Among these, as a result of intensive studies on the applied pressure and the amount of current, which are presumed to have particularly great effects, the present inventors have found conditions (preferable conditions) that allow the SmFeN magnetic particles to be decomposed without bias and appropriately. It was.

In other words, the details are left to the examination results to be described later. From the results, it was found that the area where the improvement of magnetic properties (effective current area) was observed tends to shift to the side where the amount of current is larger as the applied pressure increases. . Moreover, the range of the said effective current area | region expanded as the pressurization force increased. From these results, the present invention proposes that the SmFeN magnetic particles be decomposed under the following conditions. That is, by determining the pressure P and the current amount I so that the ratio of the current amount I [A] to the pressure force P [MPa] is 4 ≦ I / P ≦ 13, the decomposition is performed, whereby the SmFeN magnetism is obtained. The particles can be decomposed without bias and moderately.

  In this manner, if SmFeN magnetic particles are pressurized and pulsed and a part of them is decomposed, nanocomposites of SmFeN magnetic particles can be achieved. The degree of magnetic anisotropy of the SmFeN single crystal phase remaining without being decomposed may be reduced by the influence of the decomposition treatment. This is because, when isotropic magnetic measurement is performed on the magnetic particles before decomposition and the magnetic particles after decomposition, (BH) max after decomposition is improved, whereas each magnetic particle has a magnetic field. It is also inferred from the fact that when the magnetic measurement is performed after the orientation is imparted, the (BH) max after decomposition only shows a value equal to or less than that before decomposition (untreated).

  In view of such circumstances, in the present invention, pressurization energization is performed with a magnetic field applied to the SmFeN magnetic particles. As described above, the partial decomposition of the SmFeN magnetic particles by applying the pressure is performed in a state where the magnetic field is applied to the particles, so that the partial decomposition of the particles can be performed while the crystal orientation of the SmFeN magnetic particles is held by the applied magnetic field. Arise. Thereby, SmFeN nanocomposite magnetic particles having magnetic anisotropy equal to or higher than that of the SmFeN magnetic particles subjected to decomposition can be obtained.

  As described above, when applying energization under a magnetic field and partially decomposing the SmFeN magnetic particles, an arbitrary form such as direct current or pulse can be adopted as the type of current to be applied.

  Thus, according to the present invention, SmFeN nanocomposite magnetic particles that can exhibit high magnetic anisotropy as a whole particle can be provided at low cost.

  Hereinafter, 1st Embodiment of the manufacturing method of the SmFeN nanocomposite magnetic particle which concerns on this invention is described based on drawing.

FIG. 1: has shown principal part sectional drawing of the apparatus used for manufacture of the SmFeN nanocomposite magnetic particle which concerns on 1st Embodiment. This apparatus 1 is a so-called discharge plasma sintering apparatus, and contains SmFeN magnetic particles 11 made of a material to be pressurized and energized, that is, an SmFeN single crystal phase (for example, Sm ₂ Fe ₁₇ N ₃ single crystal phase). And a die 2 for insertion, and an upper punch 3 and a lower punch 4 that can be inserted into the die 2 and are arranged in a pair of upper and lower sides. An upper punch electrode 5 and a lower punch electrode 6 are provided at the ends of the upper punch 3 and the lower punch 4 opposite to the opposing sides. Of the discharge plasma sintering apparatus 1 configured as described above, at least the die 2 and the upper and lower punches 3 and 4 are accommodated in the chamber 7. The inside of the chamber 7 is maintained at a predetermined degree of vacuum (10 ⁻¹ Pa to 10 ⁻³ Pa) by an appropriate atmosphere control means (not shown), or is maintained in an inert atmosphere by nitrogen gas or the like.

  Both the upper and lower punches 3 and 4 are made of graphite in order to supply a pulse current to the SmFeN magnetic particles 11. Of course, the upper and lower punches 3 and 4 can be formed of other materials such as conductive ceramics or a high melting point metal as long as they have conductivity and strength capable of withstanding a predetermined pressure.

  The die 2 is also formed of graphite, but may be formed of other materials such as WC (tungsten carbide) or ceramics as long as it can withstand a predetermined pressure and temperature.

  The upper and lower punches 3 and 4 can be moved in the vertical direction by an appropriate driving means (not shown) through the upper punch electrode 5 and the lower punch electrode 6 and can be energized by an appropriate power supply means (not shown). ing.

With the SmFeN magnetic particles 11 filled in the space defined by the die 2 and the upper and lower punches 3 and 4, the upper punch 3 is relatively moved toward the lower punch 4 so that the SmFeN magnetic particles 11 are moved up and down. Pressurize from the direction. Along with the pressurization, a predetermined pulse current is supplied to the upper and lower punches 3, 4, and pulse energization is performed on the SmFeN magnetic particles 11 being pressed for a predetermined time. Thereby, in the SmFeN magnetic particles 11, a decomposition reaction of SmFeN → Fe + SmN + N (here, a decomposition reaction of Sm ₂ Fe ₁₇ N ₃ → 17Fe + 2SmN + 1 / 2N ₂ ) occurs.

  In this way, by applying a pressure and a pulse current to the SmFeN magnetic particles 11 and decomposing a part of the SmFeN single crystal phase forming the SmFeN magnetic particles 11, the SmFeN single crystal phase as a hard magnetic phase is decomposed. In addition, particles having a form in which Fe crystal grains as a soft magnetic phase are dispersed and precipitated are obtained. Among these, the coexistence of the SmFeN single crystal phase and the Fe crystal phase was confirmed by XRD (X-ray diffraction method). FIG. 2 is a photograph of the SmFeN magnetic particles 11 after the decomposition treatment or a part thereof taken with a TEM (transmission electron microscope). From the figure, it can be seen that the particles 11 are composed of nano-order fine crystal grains (parts indicated by arrows in the figure) that are decomposed and precipitated and SmFeN single crystal phases that remain without being decomposed. When considered together with the analysis results of the EDS (energy dispersive X-ray analyzer) and the XRD (X-ray diffraction method) shown in the upper right in the figure, it can be inferred that the fine crystal grains are precipitated Fe crystal phases. The

  As described above, by applying pulse current to the SmFeN magnetic particles 11 while applying pressure, the SmFeN magnetic particles 11 are partially decomposed to precipitate a Fe crystal phase as fine crystal grains, thereby decomposing the particles. The magnetic particles having a mixed phase structure in which the SmFeN single crystal phase as the hard magnetic phase remaining without being dispersed and the Fe crystal phase as the soft magnetic phase dispersed and precipitated in the same crystal phase and having a nano-order granularity coexist can get. The hard magnetic phase composing such particles exhibits a single crystal orientation of the SmFeN single crystal phase before decomposition. Therefore, the SmFeN composite magnetic particles obtained by such a production method can exhibit high magnetic anisotropy. Therefore, by using this as a raw material, it becomes possible to produce a nanocomposite magnet that can exhibit excellent magnetic properties {for example, (BH) max}.

  In addition, according to such a method, the manufacturing process can be simplified as compared with the conventional method, thereby making it possible to reduce the manufacturing cost of the SmFeN nanocomposite magnetic particles or the nanocomposite magnet using the same. Become.

  Further, by decomposing the SmFeN magnetic particles 11 by using the discharge plasma sintering method, the SmFeN magnetic particles 11 are uniformly decomposed throughout. Therefore, SmFeN nanocomposite magnetic particles having a homogeneous crystal structure with as little variation as possible can be obtained. Further, by using the discharge plasma sintering method, the SmFeN magnetic particles 11 can be decomposed in a short time.

  Next, the proper conditions for producing SmFeN nanocomposite magnetic particles by the above-described production method were examined by taking as an example the case of using the discharge plasma sintering method. In the following examination, the die 2 and the upper and lower punches 3 and 4 were both made of graphite, and the diameter of the accommodation space for the SmFeN magnetic particles 11 was φ10 mm.

First, among the setting conditions of the discharge plasma sintering method, regarding the five factors of the applied pressure, current amount, pulse condition, processing time (energization time), and processing atmosphere, which are presumed to affect the resolution of the SmFeN magnetic particles 11, The degree of influence of each factor on the magnetic properties, here the maximum energy product (BH) max, was examined. In particular,
1) Regarding pressure, 3kN, 4kN, 5kN,
2) Regarding the amount of current, 300A, 375A, 450A,
3) Regarding pulse conditions, 1-9, 1-1, 99-1 (the former is pulse current ON, the latter is OFF 1 unit is 1.3 msec),
4) Regarding energization time, 4 sec, 8 sec, 12 sec,
5) Regarding the atmosphere, the above decomposition treatment is performed under three levels of high vacuum (10 ^-2 to 10 ^-3 Pa), vacuum (10 ^-1 Pa), and nitrogen gas, respectively, and the SmFeN magnetic particles 11 after the treatment The magnetic properties were evaluated. At this time, the aggregate (molded body) of the processed SmFeN magnetic particles 11 isotropically, that is, after molding, the process for giving magnetic orientation in a specific magnetic field is omitted (BH) max is measured. went. Further, Z16 manufactured by Nichia Corporation was used as the SmFeN magnetic particle 11 used for the test.

  As a result, regarding the pulse condition, it was found that the condition close to direct current contributes to the improvement of (BH) max. Regarding the energization time, an optimum value exists in combination with the pulse condition, and it was found that 8 sec is suitable when the pulse condition is close to DC (99-1). On the other hand, with regard to the applied pressure, although a temporary correlation was observed between the applied pressure and (BH) max, it was found that the tendency and the degree thereof differ depending on the value of the current amount. The atmosphere did not affect the magnetic characteristics.

Based on the above results, SmFeN magnetic particles 11 under the conditions of current amount: 300 A (3.82 MA / m ² ), energization time: 8 sec, pulse condition: 99-1, pressurizing force: 5 kN (64 MPa), atmosphere: vacuum When the magnetic properties {(BH) max} of the particles after decomposition were measured, a maximum energy product of 52 kJ / m ³ was shown. Since (BH) max of the same particle 11 before decomposition was 35 kJ / m ³ , it was found that the magnetic property {(BH) max} was increased about 1.5 times by the method according to the present invention.

  Next, the magnetic characteristics {(BH) max of the decomposed SmFeN magnetic particles 11 obtained when the amount of current is changed under a pressing force of a plurality of levels (3 kN, 4 kN, 5 kN, 5.5 kN, 6 kN). } And the degree of influence of the combination of both factors on the magnetic properties was investigated. Based on the previous results, the other conditions were energization time: 8 sec, pulse condition: 99-1, and atmosphere: vacuum. (BH) max was measured isotropically on the shaped particles after decomposition.

FIG. 3 shows the relationship between the current amount I [A] under each pressing force P [kN] and (BH) max [kJ / m ³ ] obtained at that time. In the figure, a region surrounded by a broken line frame indicates a range of (BH) max that can be indicated by the SmFeN magnetic particle 11 before the decomposition treatment under the above conditions. From the figure, there is an effective current region with a predetermined width where an improvement in (BH) max is recognized at each pressing force P, and the effective current region shifts to the side where the current amount I is larger as the pressing force P increases. The tendency to do can be seen. Further, as the pressing force P increases, the range of the effective current region tends to expand. From the above results, it can be seen that an appropriate decomposition reaction can be obtained by applying a pulse current having a magnitude matching the pressure applied to the particles. FIG. 4 shows the effective current range for each applied pressure obtained from the results shown in FIG. As for the pressure value in FIG. 4, the numerical value on the left side is the set load value [kN], and the numerical value on the right side indicates the converted value to the pressure [MPa].

  By further generalizing the above results, for example, the effective range shown in FIG. 5 is determined. That is, under the conditions of energization time: 8 sec, pulse condition: 99-1, atmosphere: vacuum, the relationship between the current amount I [A] and the applied pressure P [MPa] is 4 ≦ I / P ≦ 13 (FIG. 5). By performing the above-described decomposition treatment with the applied pressure P and the current amount I set so as to satisfy the region indicated by the middle slanted line, it is possible to obtain an appropriate decomposition reaction without variation with respect to the SmFeN magnetic particles 11. . However, when the applied pressure P is too small, the macro volume resistivity of the SmFeN magnetic particles 11 increases abruptly as compared with the applied pressure P, which may cause an excessive decomposition reaction. Even if the pressure P is increased to some extent, the macro volume resistivity of the SmFeN magnetic particles 11 does not change so much, but in such a case, materials such as the die 2 and the upper and lower punches 3 and 4 that have relatively low strength. There is concern about deformation or breakage of a member formed of (graphite or the like). Therefore, from this viewpoint, in addition to the effective range shown in FIG. 5, it is preferable to appropriately determine the lower limit (for example, 38 MPa) and the upper limit (for example, 90 MPa) of the applied pressure P.

  Further, from the results shown in FIG. 3, when the pressure P is constant, it can be seen that the value of (BH) max shows a peak in the effective current region where the improvement of (BH) max is recognized. Further, the peak (maximum value) of (BH) max tends to shift in the direction in which the current amount I increases as the pressing force P increases. From this point of view, by setting the optimal amount of current I so as to obtain the maximum value (peak) of (BH) max according to the applied pressure P, it has a more ideal fine crystal mixed phase structure and is excellent. SmFeN nanocomposite magnetic particles that can exhibit magnetic properties can be obtained.

  As described above, the case where the discharge plasma sintering method (SPS method) is used as an example of the means for obtaining the SmFeN nanocomposite magnetic particles has been illustrated. As long as the particles 11 can be decomposed and the Fe crystal phase as the soft magnetic phase can be decomposed and precipitated in the SmFeN single crystal phase as the hard magnetic phase, means other than those described above can be employed.

  FIG. 6: has shown principal part sectional drawing of the apparatus used for manufacture of the SmFeN nanocomposite magnetic particle which concerns on 2nd Embodiment of this invention. The apparatus 21 mainly includes a magnetic field applying means (here, a pair of magnetic fields) for applying a predetermined magnetic field to the SmFeN magnetic particles 11 filled in a space defined by the die 22 and the upper and lower punches 23 and 24. It has a configuration different from the discharge plasma sintering apparatus 1 according to the first configuration example in that it includes an electromagnet 28). In this configuration example, the pair of electromagnets 28 is disposed opposite to the position where the die 22 is sandwiched, and a magnetic field is applied in a direction perpendicular to the movable direction of the upper and lower punches 23 and 24, that is, the energization direction to the SmFeN magnetic particles 11. It is designed to be applied.

  The point which is equipped with the die | dye 22 filled with the SmFeN magnetic particle 11, and energizing pressurization, the upper and lower punches 23 and 24, and the upper and lower punch electrodes 25 and 26 is the same as that of the 1st structural example. In this configuration example, a cylindrical chamber 27 is disposed outside the die 22, and an inert gas such as Ar is injected into the chamber 27 through a vent hole provided in the chamber 27. 22 and the upper and lower punches 23 and 24 are kept inactive.

  Similarly to the first configuration example, the upper and lower punches 23 and 24 can be moved in the vertical direction by an appropriate driving means (not shown) via the upper punch electrode 25 and the lower punch electrode 26, respectively, and appropriate electric power not shown. It can be energized by the supply means, here it is configured to be capable of direct current energization. The power supply to the electromagnet 28 and its supply source may be the same.

The SmFeN magnetic particles 11 are partially decomposed using the pressurizing and energizing device 21 having the above configuration. First, with the SmFeN magnetic particles 11 filled in the space defined by the die 22 and the upper and lower punches 23 and 24, the pair of electromagnets 28 are energized, and a predetermined magnetic field in the opposite direction is applied to the SmFeN magnetic particles 11. To do. In this manner, the SmFeN magnetic particles 11 are pressurized by the upper and lower punches 23 and 24 in a state where a magnetic field is applied, and a predetermined direct current is passed between the upper and lower punches 23 and 24, thereby energizing the SmFeN magnetic particles 11 being pressurized. Is performed for a predetermined time. Thereby, in the SmFeN magnetic particles 11, a decomposition reaction of SmFeN → Fe + SmN + N (here, a decomposition reaction of Sm ₂ Fe ₁₇ N ₃ → 17Fe + 2SmN + 1 / 2N ₂ ) occurs.

In this manner, by applying pressure and current to the SmFeN magnetic particles 11 and decomposing a part of the SmFeN single crystal phase forming the SmFeN magnetic particles 11, the hard magnetic phase is obtained as in the first embodiment. Thus, particles having a form in which Fe crystal grains as a soft magnetic phase are dispersed and precipitated in the single crystal phase of SmFeN are obtained. About the SmFeN magnetic particle 11 after the energization treatment, the Sm ₂ Fe ₁₇ N ₃ single crystal phase and the α-Fe crystal phase coexist, and the average crystallite diameter of the α-Fe crystal phase is 18 nm. This was confirmed by XRD (X-ray diffraction method).

  In this embodiment, the SmFeN magnetic particles 11 are pressurized and energized in a state where a predetermined magnetic field is applied by the electromagnet 28, so that the crystal orientation inherently possessed by the SmFeN magnetic particles 11 is determined by the applied magnetic field. Partial decomposition of the particles 11 occurs in the held state. Thereby, it has a magnetic anisotropy equivalent to or higher than that of the SmFeN magnetic particles 11 subjected to decomposition (for example, in the experiment described later, a result of improving the degree of anisotropy as illustrated in FIG. 11 was obtained). SmFeN nanocomposite magnetic particles can be obtained.

  Hereinafter, the superiority of the pressure energization method in a magnetic field application state was examined.

  First, with respect to the amount of current, pressure energization is performed in a magnetic field application state (1.2 T) or a magnetic field non-application state (0 T) under three levels of 20 A, 40 A, and 60 A (all of which are direct current). The maximum energy product (BH) max of the particles was measured. As a comparison, the (BH) max was also measured for SmFeN magnetic particles 11 of the same type (Z16 manufactured by Nichia Corporation) used in the experiment in the first embodiment and untreated.

  Here, the filling amount of the SmFeN magnetic particles 11 into the die 22 was 50 mg. The die 22 and the upper and lower punches 23 and 24 were both made of graphite, the diameter of the accommodation space for the SmFeN magnetic particles 11 was 3 mm, the pressure was 14 MPa, and the current application time was 4 s. In addition, for magnetic measurement, measurement samples are prepared by solidifying with paraffin in a state where a predetermined magnetic field is applied to the powder obtained in each of the above-described processes, and the magnetic properties of these measurement samples are expressed as VSM (vibration sample). Type magnetometer).

FIG. 7 shows the relationship between the current amount I [A] under each processing condition and (BH) max [kJ / m ³ ] obtained at that time. In any current range, the (BH) max of the particles obtained by the pressurization energization treatment with the magnetic field applied is not only the (BH) max of the untreated particles, but the pressurization energization treatment with no magnetic field applied. It can be seen that it exceeds that of the particles obtained in. Also, it can be seen that (BH) max shows the highest value (318 kJ / m ³ ) when the current amount is 40 A (= 5.66 MA / mm ² ).

Next, with respect to the energization time, the magnetic properties, specifically, the residual magnetization, of the particles obtained when the above treatments are performed under five levels of 4, 8, 10, 15, 20 [s]. Evaluation and comparison were performed for four items of Br [T], coercive force iHc [kA / m], maximum energy product (BH) max [kJ / m ³ ], and degree of anisotropy. Here, the degree of anisotropy is the ratio of magnetization at the maximum magnetic field of 2.4 MA / m in the easy magnetization direction and the two directions perpendicular to this direction (magnetization in the easy magnetization direction / magnetization in any one of the two perpendicular directions). (For other relevant indicators, refer to the following reference: Magnetic materials opened by powder metallurgy-From dust cores to permanent magnets, February 2004, Material Center, p54.) checking). The applied current amount was set to 40 A from the previous experimental result. Other conditions are the same as in the previous experiment.

  FIG. 8 shows the relationship between the energization time under each processing condition and the residual magnetization Br of the particles obtained at that time. Similarly, the relationship between the energization time and the coercive force iHc, and the energization time and (BH) max These relationships are shown in FIGS. 9 and 10, respectively. First, as shown in FIG. 8, with respect to the residual magnetization Br, the residual magnetization Br of the particles obtained by the pressurization energization treatment under the application of the magnetic field is not affected by the energization time. It turns out that it exceeds that of the particle | grains obtained by the pressurization energization process by application. Further, from FIG. 9, in the case of the pressurization energization treatment without applying a magnetic field, the coercive force iHc of the treated particles tends to decrease as the energization time increases. It can be seen that the particles suppress the decrease in the coercive force iHc. As for (BH) max, as in FIG. 7, regardless of the energization time, the (BH) max of the particles obtained by pressurization energization under magnetic field application is of course the magnetic field. It turns out that it exceeds that of the particle | grains obtained by the pressurization energization process by no application.

  Further, FIG. 11 shows the relationship between the energization time and the degree of anisotropy of the particles obtained at that time when the pressure energization treatment is performed under application of a magnetic field and when it is not treated. From the figure, it can be seen that the degree of anisotropy of particles subjected to pressurization under application of a magnetic field generally increases as compared to the degree of anisotropy of untreated particles. Also from this, SmFeN nanocomposite magnetism obtained as a result of partial decomposition is maintained by maintaining the crystal orientation of undecomposed SmFeN magnetic particles by applying pressure to the SmFeN magnetic particles while applying a predetermined magnetic field. It can be seen that high magnetic anisotropy can be imparted to the particles.

It is principal part sectional drawing of the apparatus used for the manufacturing method of the SmFeN nanocomposite magnetic particle which concerns on 1st Embodiment of this invention. It is a TEM photograph of SmFeN nanocomposite magnetic particles obtained by the manufacturing method according to the first embodiment. It is a figure which shows the relationship between the electric current amount at the time of each pressurizing force, and (BH) max of the particle | grains obtained at that time. It is a table | surface which shows the effective current range at the time of each pressurizing force. It is a figure which shows the effective range of applied pressure and electric current amount. It is principal part sectional drawing of the apparatus used for the manufacturing method of the SmFeN nanocomposite magnetic particle which concerns on 2nd Embodiment of this invention. It is a figure which shows the relationship between the electric current amount in each process condition, and (BH) max of the particle | grains obtained in that case. It is a figure which shows the relationship between the electricity supply time on each process condition, and the residual magnetization Br of the particle | grains obtained in that case. It is a figure which shows the relationship between the electricity supply time on each process condition, and the coercive force iHc of the particle | grains obtained at that time. It is a figure which shows the relationship between the electricity supply time on each process condition, and (BH) max of the particle | grains obtained in that case. It is a figure which shows the relationship between the electricity supply time on each process condition, and the degree of anisotropic of the particle | grains obtained at that time.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Discharge plasma sintering apparatus 2 Die 3, 4 Punch 5, 6 Punch electrode 11 SmFeN magnetic particle 21 Pressurization electricity supply device 22 Die 23, 24 Punch 25, 26 Punch electrode 28 Electromagnet

Claims (3)

  An SmFeN nanocomposite magnetic particle comprising an SmFeN single crystal phase as a hard magnetic phase and an Fe crystal phase as a soft magnetic phase generated by decomposing a part of the SmFeN single crystal phase.   By applying an electric current while applying pressure to the SmFeN magnetic particles, by disassembling a part of the SmFeN single crystal phase forming the SmFeN magnetic particles and precipitating the Fe crystal phase, the SmFeN single crystal phase as a hard magnetic phase is precipitated. A method for producing SmFeN nanocomposite magnetic particles, wherein magnetic particles having a mixed phase structure in which an Fe crystal phase as a soft magnetic phase is dispersed are obtained.   The method for producing SmFeN nanocomposite magnetic particles according to claim 2, wherein pressure application is performed while a magnetic field is applied to the SmFeN magnetic particles.

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