Jun-xian Zhang

Structure and magnetocrystalline anisotropy of R2Fe17−xGax compounds with higher Ga concentration

The effect of Ga substitution for Fe in R2Fe17 (R=Y, Sm, Gd, Tb, Dy, Ho, Er, and Tm) compounds on the structure and magnetocrystalline anisotropy has been studied by means of x‐ray diffraction and magnetization measurements. Both iron sublattice anisotropy and rare earth sublattice anisotropy are found to be modified by the introduction of the gallium atoms. A uniaxial anisotropy is shown in R2Fe17−xGax (for R=Y, Gd, Tb, Dy, Ho, Er, and Tm) compounds with high Ga concentration, whereas a reversal change in the easy magnetization direction is observed in the samples for R=Sm. The contributions to the uniaxial orientation of the magnetization in these compounds result from not only the rare earth sublattice, but also the iron sublattice.

Influence of Al substitution on the structure and Co-sublattice magnetocrystalline anisotropy of Gd2Co17 compounds

The structure and magnetic properties of Gd2Co17−xAlx compounds were investigated. All samples have a rhombohedral Th2Zn17-type structure and the replacement of Co by Al results in an approximately linear increase in the unit cell volumes at a rate of 8.2 A3/Al. The Curie temperature decreases monotically with the increase of Al concentration. On the basis of magnetization curves at the compensation temperature, the intersublattice-molecular-field coefficient, nRT, and the RT exchange-coupling constant JRT have been determined. It is noteworthy that the substitution of Al has a significant effect on the magnetocrystalline anisotropy of the Co sublattice, and changes the easy magnetization direction of Gd2Co17−xAlx compounds from the basal plane to the c axis.

GA-CONCENTRATION DEPENDENCE OF MAGNETOCRYSTALLINE ANISOTROPY IN GD2FE17-XGAX COMPOUNDS

The structure and magnetic properties of arc‐melted Gd2Fe17−xGax compounds were studied by means of x‐ray diffraction and magnetization measurements. X‐ray diffraction patterns demonstrate that all samples have a rhombohedral Th2Zn17‐type structure and the substitution of Ga leads to an approximately linear increase in the unit cell volumes. The Curie temperature is found to first increase and then decrease with increasing Ga concentration. It is noteworthy that the substitution of Ga has a significant effect on the magnetic anisotropy of iron sublattice. The easy magnetization direction of Gd2Fe17−xGax compounds changes from basal plane to c axis with increasing Ga concentration. The sample with x=7 exhibits a uniaxial anisotropy.

MAGNETIC-PROPERTIES OF SM2FE17-XSIX AND SM2FE17-XSIXC COMPOUNDS

Iron‐rich intermetallic compounds Sm2Fe17−xSix and Sm2Fe17−xSixC (x=0, 1, 2, and 3) were studied. The as‐prepared compounds are single phase with the rhombohedral Th2Zn17‐type structure except for Sm2Fe17C and Sm2Fe16SiC which contain some amounts of α‐Fe. The unit cell volumes and saturation magnetization at room temperature are found to decrease linearly with increasing Si concentration x. The Curie temperature Tc is found first to increase and then to decrease with increasing Si content. X‐ray diffraction measurements on magnetically aligned powder samples show that the easy magnetization direction of the Sm2Fe17−xSix samples with x≤2 is planar while that of the sample with x=3 is conical. The Sm2Fe17−xSixC samples with x≤3 exhibit an easy c‐axis anisotropy at room temperature. The anisotropy field is 83 kOe for x=0 and it rises to 110 kOe at x=1, and then drops with increasing Si concentration to 55 kOe at x=3.

Effects of Ga substitution in Y2Fe17 compounds on the magnetocrystalline anisotropy

The heating effects on the structure and fine structure of Cu-11.9Al-5Ni-1.6Mn-1Ti (wt%) shape memory alloy have been studied by means of transmission electron microscopy and microscopic compositional analysis. With the increase of the heating temperature and time, the stabilized M18R(1) martensite, transformed from the parent phase of L2(1) structure type, underwent the following structural variations: M18R(1) --> N18R(1) --> disorder N9R. Disorder N9R bainite precipitates and retained parent phases were observed in specimens heated at 573 and 623 K for 7.2 ks or longer. When the alloy was heated at 673 K for 133.2 ks, equilibrium alpha, gamma(2) and Ni,Al-rich phases were formed without any retained beta(1) parent phase. While the size of the X(s) particles decreased in the specimen heated at 623 K for 7.2 ks and they disappeared completely in the specimen heated at 673 K, the X(L) particles were coarsened after heating. With the increase of the heating temperature and time the growth of the antiphase domains was observed.

Effects of Si substitution on the magnetic properties of R2Fe17 compounds with R≡Y and Tm

Abstract X-Ray diffraction of R 2 Fe 17− x Si x (R ≡ Y and Tm) shows that the prepared samples are single phase, having the rhombohedral Th 2 Zn 17 -type structure and/or the hexagonal Th 2 Ni 17 -type structure. The substitution of Si for Fe in R 2 Fe 17 (R ≡ Y and Tm) leads to a strong increase in the Curie temperature and a reduction in the unit cell volume. The Fe moments derived from Y 2 Fe 17− x Si x decrease with increasing Si concentration from 2.0 μ B for x = 0 to 1.73 μ B for x = 3 as a result of magnetic dilution. The Tm moment is 6.0 ± 0.3 μ B , which is slightly lower than its free ion value. Samples of Tm 2 Fe 17− x Si x with x = 0–3 have a spin reorientation transition at low temperature. The spin reorientation temperature increases initially, then decreases with Si substitution, having a maximum value of 187.5 K at about x = 2.

Structure and magnetic properties of Dy2Co17−xGax (x=0–6) compounds

The structure and magnetic properties of arc-melted Dy2Co17-xGax compounds were studied. These compounds have the hexagonal Th2Ni17-type structure for 0 less than or equal to x less than or equal to 3 and the rhombohedral Th2Zn17-type structure for 3 less than or equal to x less than or equal to 6. The unit cell volume shows an approximately linear increase at a rate of about 7.7 Angstrom(3) per Ga atom. The Curie temperature was found to decrease with increasing Ga concentration. The saturation magnetization decreases linearly with increasing Ga content from 7.0 mu(B), f.u.(-1) for x=0 to -7.9 mu(B), f.u.(-1) for x=6. The exchange coupling constants J(DyCo) and J(CoCo) have been derived by analyzing both the field dependence and the temperature dependence of the magnetization. An approximately constant value of J(DyCo) indicates that the substitution of Ga for Co has only a small influence on the exchange coupling between the Dy and Co atoms. The effect of Ga substitution on J(CoCo) is strong, leading to a linear decrease of T-C in the Dy2Co17-xGax compounds

STRUCTURE AND MAGNETIC-ANISOTROPY OF SM2FE17-XALXC (X=2-8) COMPOUNDS PREPARED BY ARC MELTING

In previous work it was discovered that the 2:17‐type rare‐earth–iron compounds with high carbon concentration could be formed by the substitution of Ga, Si, or Al, etc., for Fe in R2Fe17Cx. The effect of Al substitution for Fe on the structure and magnetic anisotropy of Sm2Fe17C has been investigated. Alloys with the composition of Sm2Fe17−xAlxC (x=2, 3, 4, 5, 6, 7, and 8) were prepared by arc melting. The carbides are single phase with rhombohedral Th2Zn17‐type structure except for Sm2Fe17C which contains a small amount of α‐Fe. The addition of Al results in an approximately linear increase in the lattice constants and the unit‐cell volumes. The Curie temperature Tc is found to increase slightly when x≤3, then decrease rapidly with increasing Al concentration, while the room‐temperature saturation magnetization decreases monotonically with the addition of aluminum. X‐ray‐diffraction and magnetization measurement studies of magnetic‐field‐oriented powders demonstrate that the samples with x≤6 exhibit an ...

Effect of Ga substitution on the structure and magnetic properties of Ho2Fe17−xGax (x=0–8) compounds

The Rietveld analysis of x-ray diffraction data shows that Ho2Fe17−xGax (x=0–8) solid solutions crystallize with the Th2Ni17 structure for x⩽2, the Th2Zn17 structure for x⩾4, and the two coexisting phases for x=3. The unit-cell volume increases linearly with a slope of 8.7 A3 per Ga atom. At lower gallium concentrations, Ga atoms occupy the 18f, 18h sites in the Th2Zn17 structure (or 12j, 12k sites in the Th2Ni17 structure) and avoid the 6c, 9d sites. For higher Ga content (x⩾6) Ga atoms still avoid the 9d site, but preferentially occupy 6c and 18f sites for x=6–8 while the occupancy factor of the 18h site decreases. Gallium substitution decreases the saturation magnetization linearly with a slope of 2.5μB. The compounds Ho2Fe17−xGax (x=7,8) possess uniaxial magnetocrystalline anisotropy at room temperature. Doping first increases, then decreases the Curie temperature until this finally rebounds for x>6. The “anomalous” enhancement of the Curie temperature for x=7, 8 may be correlated with the variation o...

Effects of Ga substitution on the hard magnetic properties of the Sm2Fe17C1.5 compounds

Abstract A systematic investigation of the structure and magnetic properties of arc-melted and as-quenched Sm 2 Fe 17− x Ga x C 1.5 samples with 0 ≤ × ≤ 6 has been made by X-ray diffraction and magnetic measurements, X-ray diffraction studies have shown that these samples crystallize in the rhombohedral Th 2 Zn 17 -type structure. The unit-cell volumes υ of Sm 2 Fe 17− x Ga x C 1.5 compounds increase monotonically with increasing Ga concentration. The Ga-concentration dependence of the Curie temperature T C exhibits a maximum value of 633 K at about x = 2. The room-temperature saturation magnetization M s decreases monotonically with increasing Ga concentration. The Sm 2 Fe 17− x Ga x C 1.5 compounds exhibit an easy c -axis anisotropy at room temperature. The anisotropy field is found first to increase and then to decrease with increasing x , having a maximum value of 130 kOe at about x = 2. The coercivities of 13.0–16.0 kOe are obtained in as-quenched Sm 2 Fe 17- x Ga x C 1.5 ( x = 2 and 3) ribbons prepared at the speeds of 15–30 m/s at room temperature. The substitution of Ga in Sm 2 Fe 17 C 1.5 not only stabilizes the hard magnetic phase but also leads to the increase in coercivity.