Hua-yang Gong

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.

The formation and magnetic properties of Sm2Fe15Al2Cx (x=0-2.0) compounds prepared by arc melting

The structural and magnetic properties of compounds in the series Sm2Fe15Al2Cx have been investigated by means of x-ray diffraction (XRD) and magnetization measurements. Samples with x=0, 0.5, 1.0, 1.5, and 2.0 were prepared by the arc-melting method. XRD patterns indicate that these carbides are single phase with a rhombohedral Th2Zn17-type structure, except for Sm2Fe15Al2, which contains a few per cent of BCC alpha -Fe. The saturation magnetization for all samples is about 110 emu g-1 and has a small dependence on C concentration. The Curie temperature Tc enhancement is about 190 K for x=1.5 compared with that of Sm2Fe17. All compounds exhibit an easy c-axis anisotropy at room temperature and the anisotropy field increases to about 110 kOe when x<or=1.5. The substitution of Al, like Ga and Si, is found to not only help the formation of high-C-concentration rare-earth-Fe compounds with 2:17-type structure, but also increase the anisotropy field.

The magnetic properties of Gd2Co17−xGax compounds

X-ray diffraction (XRD) and magnetization measurements were performed to investigate the effect of Ga substitution for Co on the structural and magnetic properties of Gd2Co17−xGax compounds (x=0, 1, 2, 3, 4, 5, 6, 7, and 8). Crystal-structure studies indicate that all samples are single phase with the rhombohedral Th2Zn17-type structure except for the samples with x=7 and 8, which contain a small amount of Co. The Ga substitution for Co in Gd2Co17 compounds leads to a monotonic increase in the unit cell volume and an approximately linear decrease in the saturation magnetization. The Curie temperature TC is found to decrease monotonically from 1210 K for x=0 to 30 K for x=8. The compensation points are observed for the Gd2Co17−xGax samples with x=5 and 6. The value of the compensation temperature, determined from the temperature dependence of the magnetization measured in a magnetic field of 1000 Oe, is 120 and 152 K for x=5 and 6, respectively. It is noteworthy that the substitution of Ga for Co in the Gd...

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.

Magnetic properties of Sm2Fe17-xGaxC2 compounds

The Sm2Fe17-xGaxC2 (x=0, 2, 3, 4, 5 and 6) samples were prepared by arc melting. X-ray diffraction shows that these alloys are single-phase compounds of the rhombohedral Th2Zn17-type structure except for the sample with x=0, which exhibits a multiphase structure with a predominant alpha -Fe phase. The lattice constants a and c and the unit-cell volumes nu of Sm2Fe17-xGaxC2 compounds with x>or=2 increase monotonically with increasing Gax concentration. The Curie temperature TC and room-temperature saturation magnetization Ms are found to decrease monotonically with increasing Gax concentration x from 635 to 338 K and from 102.3 to 29.0 emu g-1 respectively, as x increases from 2 to 6. The Sm2Fe17-xGaxC2 compounds exhibit an easy c axis anisotropy. The room-temperature anisotropy field is 135 kOe for x=2, which is about 55 kOe higher than that of Nd2Fe14B, and it decreases to 60 kOe at x=4.

Magnetic properties of R2Fe14M3 compounds with M=Ga and Si; R=Y, Nd, Sm, Gd, Tb, Dy, Ho, Er and Tm

Samples with composition R2Fe14M3 (M = Ga and Si; R = Y, Nd, Sm, Gd, Tb, Dy, Ho, Er and Tm) have been prepared by are-melting. Crystal-structure studies have shown that the prepared samples are single phase with the rhombohedral Th2Zn17 and/or the hexagonal Th2Ni17 structure. Substitution of Ga for Fe in R2Fe17 leads to an increase of the unit-cell volume, whereas Si substitution reduces the unit-cell volume. The Curie temperatures of the R2Fe14Ga3 and R2Fe14Si3 compounds are much larger than those of the corresponding R2Fe17 compounds. The Fe moment decreases upon Ga or Si substitution. The compounds R2Fe14Ga3 and R2Fe14Si3 With R = Er and Tm exhibit a spin-reorientation transition at low temperature

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.

Magnetic anisotropy of Dy2Fe17−xGax compounds

Abstract The single-phase compounds of Dy2Fe17−xGax (x = 0, 1, 2, 3, 4, 5, 6, 7 and 8) were prepared by arc melting. The substitution of Ga in the Dy2Fe17 compound is found to have an important effect on their structure and magnetic properties. Dy2Fe17 sample has the hexagonal Th2Ni17-type structure and the Ga-substituted samples crystallize in the rhombohedral Th2Zn17-type structure. The unit cell volumes increase linearly with increasing gallium concentration. The Curie temperature is found first to increase and then to decrease with increasing gallium content x, attaining a maximum value of 557 K at about x = 3, which is 187 K higher than that of Dy2Fe17. The saturation magnetization decreases linearly with increasing gallium content from 15.13 μB/f.u. for x = 0 to −4.27 μB/f.u. for x = 8. For x ≈ 6, the Fe sublattice moment is found to be about equal to the Dy sublattice moment. X-ray diffraction measurements on magnetically aligned powder samples reveal a change in easy magnetization direction, and the samples with x ≤ 5 exhibit easy plane anisotropy while the samples with x ≥ 6 exhibit easy c-axis anisotropy at room temperature.

MAGNETIC AND MAGNETORESTRICTIVE PROPERTIES OF SM1-XDYXFE2 COMPOUNDS AND ITS MOSSBAUER-EFFECT STUDIES

Measurements of x‐ray diffraction, magnetization, magnetostriction, and Mossbauer effect were performed on a series of Sm1−xDyxFe2 samples (x=0, 0.1, 0.15, 0.25, 0.45, and 0.65). It is shown that the system retains the cubic MgCu2 structure over the whole range and the lattice constant decreases linearly with increasing x. Results of Mossbauer effect study at room temperature show that for a small amount of Dy substitution for Sm, x<0.15, easy axes of the magnetization keep in the [111] direction. For x≳0.15, the direction of easy axes rotates gradually from [111] for x=0, and 0.1 to [100] for x=0.45 and 0.65. The concentration dependence of the saturation magnetization exhibits a minimum at x=0.30 for 1.5 K and at x=0.45 for room temperature, reflecting the occurrence of the compensation of magnetic moments at various Sm/Dy ratios. For x=0.45 and 0.65, the pinning phenomenon of narrow domain walls was observed at low temperature. The magnetostriction was found to decrease with the increase in the Dy cont...