JP2017152609A - Magnetic material - Google Patents

Abstract

PROBLEM TO BE SOLVED: To solve the problem in which, in a conventional magnetic material having Fe-Pd as a core and Fe as a shell, when a reverse magnetic field is applied to the magnetic material, the Fe of the shell is magnetically reversed, thereby disabling to obtain a high coercive force of the whole magnetic material and to supply magnetic material with high coercivity.SOLUTION: The magnetic material includes: a core containing Fe-Pd; a shell containing Fe; and a coating present on the outer periphery of the shell and containing SiO. A ratio c/a of crystal lattice constants a and c of the Fe-Pd is 0.957 to 0.961.SELECTED DRAWING: Figure 1

Description

  The present invention relates to a magnetic material containing Fe—Pd as a hard magnetic material phase. The present invention particularly relates to a magnetic body including a core containing Fe—Pd and a shell containing Fe.

  In order to improve the magnetic anisotropy and / or the coercive force, the magnetic material containing Fe—Pd as the hard magnetic material phase has been variously improved.

For example, Patent Document 1 discloses a magnetic body in which Fe—Pd is coated with SiO ₂ . Since the Fe—Pd particles are not fused to each other by coating SiO ₂ , the magnetic material disclosed in Patent Document 1 has high magnetic anisotropy.

  Patent Document 2 discloses a magnetic body having Fe—Pd as a core and Fe as a shell. Fe—Pd is a hard magnetic phase, and Fe is a soft magnetic phase. By making Fe—Pd and Fe into a core / shell structure, exchange coupling works between the hard magnetic phase and the soft magnetic phase, so that the residual magnetization and saturation magnetization of the magnetic material can be improved.

International Publication No. 2006/070572 Japanese Patent Laying-Open No. 2015-185602

  However, the magnetic material disclosed in Patent Document 2 cannot obtain a high coercive force due to the influence of Fe which is a soft magnetic material phase. FIG. 4 is a schematic diagram for explaining the reason why a conventional magnetic body using Fe—Pd as a core and Fe as a shell cannot obtain a high coercive force.

  The conventional magnetic body 10 has an Fe—Pd core 1 and an Fe shell 2. As shown in FIG. 4A, when no magnetic field is applied to the conventional magnetic body 10, the direction of the magnetic field is the same in the core 1 and in the shell 2. However, when a magnetic field opposite to the magnetic field inside the core 1 and the inside of the shell 2 is applied to the conventional magnetic body 10, the shell 2 has a soft magnetic phase. As shown in FIG. 4B, the magnetic field in the core 1 is opposite. If it does so, as shown in FIG.4 (c), the magnetic field inside the core 1 will also become the same direction as the applied magnetic field, and the conventional magnetic body 10 cannot obtain a high coercive force.

  As described above, in a conventional magnetic body having Fe—Pd as a core and Fe as a shell, when a reverse magnetic field is applied to the magnetic body, the Fe of the shell is magnetically reversed. The present inventors have found a problem that a high coercive force cannot be obtained.

  The present invention has been made to solve the above problems, and the present invention provides a magnetic body having a core containing Fe—Pd and a shell containing Fe and having a high coercive force. For the purpose.

In order to achieve the above object, the present inventors have made extensive studies and completed the present invention. The summary is as follows.
<1> a core containing Fe—Pd;
A shell containing Fe;
A film present on the outer periphery of the shell and containing SiO ₂ ;
With
C / a in the crystal lattice constants a and c of the Fe—Pd is 0.957 to 0.961.
Magnetic material.

  ADVANTAGE OF THE INVENTION According to this invention, the magnetic body provided with the core containing Fe-Pd and the shell containing Fe and having a high coercive force can be provided.

Case the core is a case and _Fe 68 _{Pd 32} is a _Fe 65 _{Pd 35,} a diagram showing the relationship between the thickness and the coercive force of the film (SiO _2). Case the core is a case and _Fe 68 _{Pd 32} is a _Fe 65 _{Pd 35,} a diagram showing the relationship between the thickness and the c / a of the film (SiO _2). FIG. 4 is a diagram showing a structure of a magnetic body in Example 2. (A) is a figure which shows the structure | tissue observed using the transmission electron microscope (TEM), (b) shows the structure | tissue observed using the high angle scattering dark field scanning transmission electron microscope (HAADF-STEM). FIG. It is a schematic diagram explaining the reason why a conventional magnetic body using Fe—Pd as a core and Fe as a shell cannot obtain a high coercive force.

  Hereinafter, embodiments of the magnetic body according to the present invention will be described in detail. In addition, embodiment shown below does not limit this invention.

The magnetic body of the present invention includes a core containing Fe—Pd, a shell containing Fe, and a coating film present on the outer periphery of the shell and containing SiO ₂ .

(core)
The magnetic body of the present invention includes a core containing Fe—Pd at the center. Fe-Pd represents an alloy of Fe (iron) and Pd (palladium).

The composition of Fe—Pd is not particularly limited as long as Fe—Pd is a hard magnetic phase. When the composition of Fe—Pd is expressed as Fe _x Pd _y (where x + y = 100), x is 45 to 85 atomic% and y is 15 to 55 atomic% from the viewpoint of the magnetic properties of the hard magnetic phase. Is preferred. Examples of Fe—Pd include Fe ₆₅ Pd ₃₅ and Fe ₆₈ Pd ₃₂ .

  Fe-Pd is an alloy of Fe (iron) and Pd (palladium), but Fe-Pd may contain elements other than Fe and Pd as long as the magnetic properties as a hard magnetic phase are not impaired. Good. The purity of Fe—Pd is preferably 97% by mass or more, and more preferably 99% by mass or more.

  The core may contain an alloy, metal, oxide, and / or nitride other than Fe—Pd as long as the magnetic properties of the Fe—Pd hard magnetic phase are not impaired. When the entire core is 100% by mass, the content of Fe—Pd in the core is preferably 97% by mass or more, and more preferably 99% by mass or more.

  Moreover, when the whole magnetic body is 100 volume%, it is preferable that content of a core is 50-99 volume%. By making the core content within this range, the exchange coupling described later works effectively. In addition, the whole magnetic body is the sum total of the volume% of a core, a shell, and each film.

  Although there is no restriction | limiting in particular in the magnitude | size of a core, It is preferable that the magnitude | size of a core is a circle equivalent diameter and 1-1000 nm. If the size of the core is within this range, the core exhibits more excellent characteristics as a hard magnetic phase. The size of the core is more preferably 10 to 100 nm as an equivalent circle diameter. The equivalent circle diameter is the projected area equivalent circle diameter. The same applies hereinafter unless otherwise specified.

(shell)
The magnetic body of this invention is equipped with the shell containing Fe in the outer periphery of the core mentioned above. Fe may contain (solid solution) elements other than Fe as long as the magnetic properties of Fe as a soft magnetic phase are not impaired. The purity of Fe is preferably 97% by mass or more, and more preferably 99% by mass or more.

  The shell may contain a metal other than Fe, an alloy, an oxide, and / or a nitride as long as the magnetic properties of Fe as a soft magnetic phase are not impaired. When the entire shell is 100% by mass, the Fe content in the shell is preferably 97% by mass or more, and more preferably 99% by mass or more.

  Since the magnetic body of the present invention has a core / shell structure, exchange coupling is performed between the core containing Fe-Pd, which is a hard magnetic phase, and the shell containing Fe, which is a soft magnetic phase. Work. Due to this exchange coupling, the magnetic body of the present invention has more excellent remanent magnetization and saturation magnetization than a magnetic body of a single core without a shell.

  In order to make this exchange coupling work more effectively, the content of the shell is preferably 1 to 50% by volume when the entire magnetic material is 100% by volume. In addition, the whole magnetic body is the sum total of the volume% of a core, a shell, and each film.

  The thickness of the shell is not particularly limited, but the thickness of the shell is preferably 0.1 to 100 nm. If the thickness of the shell is within this range, the shell can exhibit more excellent characteristics as a soft magnetic phase and can more effectively act as an exchange with the core. The thickness of the shell is more preferably 1 to 10 nm.

(Coating)
The magnetic body of the present invention includes a coating that exists on the outer periphery of the shell and contains SiO ₂ . The film containing SiO ₂ can change the crystal lattice constants a and c / a of Fe—Pd. SiO ₂ may be amorphous or crystalline. Further, SiO ₂ may be a complex oxide containing an element other than Si and O as long as the function of changing c / a described above is not impaired. The purity of SiO ₂ is preferably 97% by mass or more, and more preferably 99% by mass or more.

The coating may contain oxides, nitrides, metals, and / or alloys other than SiO ₂ as long as the above-described function of changing c / a is not impaired. When the entire coating is 100% by mass, the content of SiO _{2 in} the coating is preferably 97% by mass or more, and more preferably 99% by mass or more.

  Moreover, when the whole magnetic body is 100 volume%, it is preferable that content of a film is 0.1-10 volume%. By setting the content of the coating within this range, the above-described function of changing c / a works effectively. In addition, the whole magnetic body is the sum total of the volume% of a core, a shell, and each film.

The thickness of the coating is preferably 1 to 13 nm. If the thickness of the coating is within this range, the above-described function of changing c / a works more effectively. In addition, since the magnetic body of the present invention is often nanoparticles, the magnetic bodies are often sintered or connected with a binder or the like. In such a case, the coating containing SiO ₂ also functions as a film that divides magnetism.

(C / a in Fe-Pd crystal lattice constants a and c)
C / a (hereinafter, simply referred to as “c / a”) in the crystal lattice constants a and c of Fe—Pd is 0.957 to 0.961. The crystal lattice constant means the length of the crystal axis and the angle between the crystal axes. These are represented by six constants: the angles α, β, and γ between the edges of the crystal unit cell, and the lengths a, b, and c of each axis.

  By setting c / a to 0.957 to 0.961, the magnetic anisotropy of Fe—Pd can be increased. Thereby, even if a magnetic field in the direction opposite to the magnetic field inside the core is applied to the magnetic body of the present invention, the decrease in the coercive force of the magnetic body is suppressed. As a result, the magnetic body of the present invention has a higher coercive force than a conventional magnetic body including a core containing Fe—Pd and a shell containing Fe.

Without being bound by theory, due to the presence of a coating containing SiO ₂ , strain is introduced into a magnet including a core containing Fe—Pd and a shell containing Fe, so that c / a is 0.957-0. .961.

(Method for producing magnetic substance of the present invention)
Although the manufacturing method of the magnetic body of this invention will not be specifically limited if the magnetic body obtained satisfies the requirements demonstrated so far, For example, the following manufacturing methods can be mentioned.

  Pd particles are produced. The method for producing Pd particles is not particularly limited, and examples thereof include a method for producing Pd nanocube particles by a chemical reduction method. The size of the Pd nanocube particles is preferably 1 to 100 nm, more preferably 5 to 50 nm, in terms of equivalent circle diameter.

The outer periphery of the Pd particles is coated with iron oxide to obtain particles whose core is Pd and whose shell is FeO _x (hereinafter, such particles may be referred to as “Pd / FeO _x particles”). Method for coating the outer peripheral iron oxide of Pd particles is not particularly limited, a mixture of Fe _{(CO) 5} in Pd particles, Fe _{(CO) 5} method of degrading the like.

Pd / FeO _x particles added tetraethylorthosilicate (Tetraethyl Orthosilicate), Pd / FeO x particles periphery to particles coated with SiO ₂ (hereinafter, such particles, and "pd _/ FeO x / SiO ₂ particles" May be represented.) The thickness of the SiO ₂ coating of Pd / FeO _x / SiO ₂ particles is controlled by the amount of tetraethyl orthosilicate.

In a reducing atmosphere, Pd / FeO _x / SiO ₂ particles are subjected to a reduction heat treatment, particles in which the core is Fe—Pd, the shell is Fe, and the outer periphery of the shell is coated with SiO _2. May be referred to as “Fe—Pd / Fe / SiO ₂ particles”. )

  The reducing gas is not particularly limited, but the reducing gas is preferably hydrogen gas from the viewpoint that it is difficult to produce a compound with Fe, Pd, and Si.

The reduction heat treatment temperature may be appropriately determined depending on the composition of Fe—Pd of Fe—Pd / Fe / SiO ₂ particles, etc., with 500 to 600 ° C. as a guide.

  When reducing the Fe concentration (atomic%) in Fe—Pd, the reduction heat treatment temperature is increased. On the other hand, when the Fe concentration (atomic%) in Fe—Pd is increased, the reduction heat treatment temperature is decreased.

In the case of Fe ₆₅ Pd ₃₅ , the reduction heat treatment temperature may be 545 to 555 ° C., for example. In the case of Fe ₆₈ Pd ₃₂ , the reduction heat treatment temperature may be, for example, 525 to 535 ° C.

The reduction heat treatment time may be appropriately determined depending on the amount of treatment of Fe—Pd / Fe / SiO ₂ particles. The reduction heat treatment time is preferably 1 to 50 hours, more preferably 5 to 15 hours.

  The manufacturing method described so far may be modified as follows, for example, as long as the purpose is not impaired.

When the Fe—Pd of the Fe—Pd / Fe / SiO ₂ particles contains an element other than Fe and Pd, the Pd particle may be a particle containing Pd and an element other than Fe and Pd. The core of the Fe-Pd / Fe / SiO ₂ particles (particles comprised of core / shell / coating) In case of containing alloy or the like other than Fe-Pd is the Pd particles, and Pd, Fe-Pd alloy It is good also as the particle | grains containing constituent elements, such as.

The Fe-Pd / Fe / SiO ₂ particles Fe, in case of incorporating (solid solution) elements other than Fe, the FeO _x of Pd / FeO _x particles contains a FeO _x, and elements other than Fe May be. The shell of the Fe-Pd / Fe / SiO ₂ particles (particles comprised of core / shell / coating), in case of incorporating a metal other than Fe and / or alloys such as, FeO _x of Pd / FeO _x particles , FeO _x and a metal other than Fe and / or a constituent metal of an alloy may be contained.

SiO ₂ of Fe-Pd / Fe / SiO ₂ particles, in the case of a composite oxide containing an element other than Si and O, Pd / to FeO _x particles, and tetraethylorthosilicate, elements other than Si and O A silicate containing may be added. When the coating of Fe—Pd / Fe / SiO ₂ particles (particles composed of core / shell / coating) contains an oxide other than SiO ₂ , tetraethyl orthosilicate is added to the Pd / FeO _x particles. , And a silicate containing an element constituting an oxide other than SiO ₂ may be added.

  Hereinafter, the present invention will be described more specifically with reference to examples. Note that the present invention is not limited to these.

Example 1
Pd nanocube particles having an equivalent circle diameter of 10 to 20 nm were prepared by a chemical reduction method. After the Pd nanocube particles and Fe (CO) ₅ were mixed, Fe (CO) ₅ was decomposed to produce Pd / FeO _x particles.

In order to reduce the Pd / FeO _x particles to make the core composition Fe ₆₅ Pd ₃₅ , 0.03 mmol of tetraethyl orthosilicate was added to 40 mg of Pd / FeO _x particles, and Pd / FeO _x / SiO ₂ particles were prepared.

The Pd / FeO _x / SiO ₂ particles were subjected to a reduction heat treatment in a hydrogen atmosphere at 550 ° C. for 10 hours to produce Fe—Pd / Fe / SiO ₂ particles. The Fe—Pd / Fe / SiO ₂ particles were used as the magnetic material of Example 1. The reduction heat treatment temperature was set with the goal of setting the Fe—Pd composition to Fe ₆₅ Pd ₃₅ .

(Examples 2-9)
Magnetic materials of Examples 2 to 9 were prepared in the same manner as in Example 1 except for the amount of tetraethyl orthosilicate added to 40 mg of Pd / FeO _x particles. The addition amount of tetraethyl orthosilicate in Examples 2 to 9 was 0.05 mmol, 0.10 mmol, 0.14 mmol, 0.18 mmol, 0.23 mmol, 0.32 mmol with respect to 40 mg of Pd / FeO _x particles, respectively. 0.45 mmol and 0.90 mmol.

(Examples 10 to 13)
In order to reduce the Pd / FeO _x particles so that the core composition is Fe ₆₈ Pd ₃₂ , Example 1 is the same as Example 1 except that the amount of tetraethyl orthosilicate added and the reduction heat treatment temperature is 530 ° C. 10 to 13 magnetic materials were produced. The reduction heat treatment temperature was set with the goal of setting the Fe—Pd composition to Fe ₆₈ Pd ₃₂ . Moreover, the addition amount of the tetraethyl orthosilicate of Examples 10-13 was 0.05 mmol, 0.10 mmol, 0.14 mmol, and 0.18 mmol with respect to 40 mg of Pd / FeO _x particles, respectively.

(Comparative Example 1)
A magnetic material of Comparative Example 1 was produced in the same manner as in Example 1 except that tetraethyl orthosilicate was desired to be added to the Pd / FeO _x particles.

(Comparative Example 2)
A magnetic material of Comparative Example 2 was produced in the same manner as in Example 10 except that tetraethyl orthosilicate was added to the Pd / FeO _x particles.

(Reference Example 1)
A magnetic material of Reference Example 1 was produced in the same manner as in Example 1 except that tetraethyl orthosilicate was not added to the Pd / FeO _x particles and the reduction heat treatment temperature was 570 ° C. The reductive heat treatment temperature was set with the goal of making the composition of Fe—Pd Fe ₆₀ Pd ₄₀ and not having a core / shell structure and a magnetic material only with a core.

(Evaluation of magnetic material)
Each magnetic material produced in this way was evaluated as follows.

(Magnetic properties)
As for the magnetic characteristics, the coercive force of each magnetic material was measured at room temperature using a vibrating sample magnetometer (VSM: Vibrating Sample Magnetometer).

(Crystal lattice constant)
As for the crystal lattice constant, each magnetic substance is analyzed by X-ray diffraction (XRD), and crystal lattice constants α, β, and γ, and a, b, and c are calculated from the analysis results. Furthermore, c / a was determined.

(Tissue observation)
The structure of each magnetic material was observed using a transmission electron microscope (TEM) and a high-angle scattering dark-field scanning transmission electron microscope (HAADF-STEM). Then, it was confirmed whether each magnetic body has a core / shell structure.

The result of observing the structure of the magnetic body of Example 2 is shown in FIG. (A) shows the structure | tissue observed using the transmission electron microscope, (b) shows the structure | tissue observed using the high angle scattering dark field scanning transmission electron microscope. In (a), due to the difference in contrast, core / shell type particles (hereinafter sometimes referred to as “Fe—Pd / Fe particles”) in Fe—Pd / Fe / SiO ₂ particles and a coating (SiO ₂ ). ). From (a), the diameter of the Fe—Pd / Fe / SiO ₂ particles and the diameter of the Fe—Pd / Fe particles were measured, and the half of the difference was taken as the thickness of the coating (SiO ₂ ). Determined the thickness of the SiO ₂ for 200 Fe-Pd / Fe / SiO ₂ particles randomly extracted, results of calculating the average value was 3.0 nm. For the Fe—Pd / Fe / SiO ₂ particles other than Example 2, the thickness of the coating (SiO ₂ ) was similarly determined. In (b), since the coating SiO ₂ is amorphous, the coating is not observed, but the core (Fe—Pd) and the shell (Fe) can be clearly distinguished from the difference in contrast. The same applies to Fe—Pd / Fe / SiO ₂ particles other than Example 2. From these results, it was confirmed that the magnetic bodies of Examples 1 to 13 had a core / shell / coating structure.

Table 1 shows the evaluation results of the coercive force and c / a. Also, from Table 1, the relationship between the thickness of the coating (SiO ₂ ) and the coercive force when the core is Fe ₆₅ Pd ₃₅ and Fe ₆₈ Pd ₃₂ is summarized in FIG. Furthermore, the relationship between the thickness of the coating (SiO ₂ ) and c / a when the core is Fe ₆₅ Pd ₃₅ and Fe ₆₈ Pd ₃₂ is summarized in FIG. In Table 1 and FIGS. 1 and 2, the thickness of the coating (SiO ₂ ) of 0 nm means that the coating (SiO ₂ ) does not exist.

As can be seen from Table 1 and FIGS. 1 and 2, in the magnetic materials of Examples 1 to 13, c / a became 0.957 to 0.961 due to the presence of the coating (SiO ₂ ), and as a result, It has confirmed that the magnetic body of Examples 1-13 has a high coercive force. Furthermore, it confirmed that the magnetic body of Examples 1-13 had a higher coercive force compared with the magnetic body of the reference example 1 which is not provided with a shell.

  From the above results, the effect of the present invention was confirmed.

1 Core 2 Shell 10 Conventional magnetic material

Claims (1)

A core containing Fe-Pd;
A shell containing Fe;
A film present on the outer periphery of the shell and containing SiO ₂ ;
With
C / a in the crystal lattice constants a and c of the Fe—Pd is 0.957 to 0.961.
Magnetic material.