JPH07126815A - Permanent magnet material - Google Patents

Abstract

PURPOSE:To develop a permanent magnet having excellent magnetic properties without using expensive rate earth elements by forming the crystal structure of a permanent magnet essentially consisting of Fe, Co and specified metals into a specified body-centered tetragonal structural body. CONSTITUTION:High purity Fe, Co and Pd or Pt is subjected to arc melting in an inert atmosphere of Ar or the like into an alloy having a compsn. of FeCo1-xPdx or FeCo1-xPtx (where x satisfies 0.2<=x<=0.9), and the slab is subjected to heat treatment, e.g. at 1100 deg.C for 20hr in a magnetic field and is thereafter rapidly cooled to a room temp. The permanent magnet in which a CuAu type body-centered tetragonal structural body embracing Co, Pd and Pt at the body-centered position forms a main phase, the C axis is used as an easily-magnetized axis and the crystal magnetic anisotropy energy at a room temp. is regulated to >=10<5>J/m<3> and excellent in magnetic properties can be obtd. without using easily oxidizable expensive rare earth elements.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a permanent magnet material used for a speaker, a VCM, a rotator and the like.

[0002]

2. Description of the Related Art Rare earth magnets currently in practical use are roughly classified into Sm-Co type and Nd-Fe-B type. The former has a high coercive force and excellent temperature characteristics, but has a drawback that the saturation magnetization M is low. This was originally solved by the development of an Nd-Fe-B system using Fe with a large M as a base, and since it also did not contain expensive Co, it was industrially shifted to an Nd-Fe-B system magnet. It's starting. However, the Nd-Fe-B system has a problem that it has a low Curie temperature and is easily oxidized, and development is currently underway as a countermeasure against it. In particular, the problem of oxidation adversely affects not only the corrosion resistance but also the magnetic properties themselves, and the reduction of oxygen in the manufacturing process greatly affects the manufacturing cost. This is a problem that can be said to be the fate of using rare earths as a raw material in addition to the use of Fe, and can be said to be a general problem of rare earth magnets.

[0003]

DISCLOSURE OF THE INVENTION The present invention provides an excellent permanent magnet material having high magnetic characteristics without using a rare earth element which is expensive and has a problem of oxidation.

[0004]

The present inventor has found that even if a part of Pd or Pt of FePd or FePt having a CuAu type structure distorted in a tetragonal structure (FIG. 1) is replaced with Co, the tetragonal structure is maintained. Moreover, it was found that the crystalline magnetic anisotropy energy was larger than that before substitution and the magnetization was also increased, and the present invention was completed. The background and contents of the present invention will be described below.

Among the magnetic properties required for a permanent magnet, magnetization and uniaxial crystal magnetic anisotropy are the most important and indispensable properties. Regarding the magnetization, in the alloy of 3d transition metal which is the main role of the magnetic material, a large value is shown in the bcc-FeCo alloy as seen in the Slater-Pauling curve, but the crystal structure is cubic except for Co alone. Yes,
Only hcp-Co exhibits uniaxial anisotropy. On the other hand, in the ordered alloy of 3d transition metal and 4d transition metal, CoP
CuA with extended c-axis like t, FePd, FePt, etc.
has a u structure or a tetragonal structure described by L1 ₀ ,
Those having strong uniaxial magnetocrystalline anisotropy are known. However, since Pd and Pt have almost no magnetic moment, their average magnetic moment or magnetization is close to half that of Fe or Co metal.

However, if a part of Pt or Pd occupying the body-centered position of the CuAu structure is replaced with Co, the system increases by the magnetic moment of Co, and if the tetragonal structure is maintained, this system is maintained. Is expected to be a material having high magnetic anisotropy and high magnetization. Therefore, the present inventor examined the possibility of FeCo _1-X Pd _X (X = 1,0.5) as a permanent magnet from band calculation based on the local density functional approximation.

FIG. 2 shows a CuAu structure FeCo _0.5 Pd _0.5.
Is a plot of the total energy of the system when the lattice constant ratio is c / a = 1.0, 1.2 and 1.3 as a function of the Wigner-Seitz radius r _WS corresponding to the lattice constant. The energy of the system at r _WS which gives the minimum energy in the case of c / a = 1.2 than in c / a = 1.0
Is low, so at least this system has c / a = 1.
It is expected that the tetragonal crystal with c / a> 1 will be more stable than the cubic crystal with 0. Figure 3 shows FePd and FeCo _0.5 Pd
It is a calculation result of c / a dependence of magnetization of _0.5 . FePd
Pd at the actual lattice constant ratio c / a of 1.3576
It can be seen that the magnetization is certainly increased in FeCo _0.5 Pd _0.5 in which half of the above is replaced by Co. However, FeCo _0.5 Pd
_In the case of _0.5 , c / a = which seems to be stable in terms of energy
It can be seen that the magnetization is further increased in 1.2. Therefore, when Pd is replaced by Co, it is expected that the magnetization is increased not only by the effect of atom replacement but also by the contraction of c / a. Figure 4 shows FePd and FeCo _0.5 P
It is a calculation result of c / a dependence of crystal magnetic anisotropy energy-Ku of d _0.5 . Actual lattice constant ratio c / a of FePd
= 1.3576, the Ku is about 25 × 10 ⁵ J / m ³ , and the calculated values show a good agreement. It is easily understood that Ku decreases in both FePd and FeCo _0.5 Pd _0.5 when c / a decreases, as a result of the fact that they approach a highly symmetric cubic crystal. What should be noted here is that FeCo _0.5 Pd _0.5 has a larger anisotropic energy than FePd. Originally FeP
It is Pd and Pt that d and FePt show strong magnetic anisotropy.
Has a very large spin-orbit interaction energy compared to Fe and Co.
It is a very interesting result that the magnetic anisotropy becomes stronger by substituting a part with. This is because both spin-orbit interaction and exchange interaction are involved in magnetic anisotropy.
It is interpreted that the substitution of o promotes exchange splitting and thus affects the magnetic anisotropy. The above results are FeP
It was qualitatively the same at t, and the calculation result was obtained that not only the magnetization but also the magnetic anisotropy energy increased by substituting a part of Pt with Co.

Based on the above calculation results, the inventor has found that FeC
o _1-X Pd _X and FeCo _1-X Pt _X were prepared and magnetic properties were evaluated. As a result, an increase in magnetization and good uniaxial anisotropy were confirmed in the range of 0.2 ≦ X ≦ 0.9. Was done. X
When <0.2, the system becomes cubic and uniaxial anisotropy cannot be obtained. Further, when X> 0.9, the effect of Co substitution was not recognized and good characteristics were not obtained.

[0009]

EXAMPLES The present invention will be described below with reference to examples. Purity 99.9% iron and purity 99.9% Co and purity 9
9.7% Pd is arc-melted in Ar atmosphere to produce FeC
o _1-X Pd _X (X = 0.3, 0.4, 0.5, 0.
A disordered alloy of 6) was obtained. After that, heat treatment was performed at 1100 ° C. for 20 hours in a magnetic field, and the mixture was gradually cooled to room temperature to obtain a regular single phase. Table 1 shows the obtained magnetic characteristics.

[0010]

[Table 1] M: Magnetization (room temperature), Tc: Curie temperature, Ku: Crystal magnetic anisotropy energy (room temperature)

Table 2 shows FeCo obtained by a similar method.
The magnetic characteristics of _1-X Pt _X (X = 0.3, 0.4, 0.5, 0.6) are shown.

[0012]

[Table 2] M: Magnetization (room temperature), Tc: Curie temperature, Ku: Crystal magnetic anisotropy energy (room temperature)

[0013]

According to the specific alloy composition of the present invention, a permanent magnet material having excellent magnetic properties can be obtained without using a rare earth element.

[Brief description of drawings]

FIG. 1 is a diagram showing a crystal structure of a CuAu type ordered alloy.

FIG. 2 is a graph showing the Wigner-Seitz radius r _WS (atomic unit) dependence of the crystal energy at each lattice constant ratio of FeCo _0.5 Pd _0.5 .

FIG. 3 is a graph showing the dependence of the magnetization M of FePd and FeCo _0.5 Pd _0.5 on the lattice constant ratio c / a.

FIG. 4 is a graph showing the c / a dependence of crystal magnetic anisotropy energy of FePd and FeCo _0.5 Pd _0.5 .

─────────────────────────────────────────────────── ─── Continuation of the front page (51) Int.Cl. ⁶ Identification code Internal reference number FI Technical indication H01F 7/02 C

Claims (3)

[Claims] 1. Fe, Co, and M (M: Pd, Pt)
A permanent magnet material containing a CuAu-type body-centered tetragonal structure having Co and M at the body-centered position as a main phase. 2. FeCo _1-X M _X (where 0.2 ≦ x ≦
The permanent magnet material according to claim 1, having a composition of 0.9). 3. The permanent magnet according to claim 1, wherein the c-axis is the axis of easy magnetization and the magnetocrystalline anisotropy energy at room temperature is 10 ⁵ J / m ³ or more.