Ying-chang Yang

Structural and magnetic properties of Y(Mn1−xFex)12

The crystallographic and the magnetic structures of Y(Mn1−xFex)12 intermetallic compounds were investigated. They crystallize in the ThMn12 structure type. The Y atoms occupy the 2(a) sites and the transition metals are distributed on 3 nonequivalent sites 8i, 8j, and 8f. We have determined the solid solubility limit (x = 0.67) of Fe in YMn12. Neutron diffraction spectra at different temperatures have been used to study the nuclear and magnetic structure of Y(Mn0.7Fe0.3)12 and Y(Mn0.4Fe0.6)12. The Mn and Fe atoms are found to exhibit strong site preference with the i site favoring Mn atoms and the f site Fe atoms. Accordingly the instability of the RFe12 phase can be explained on the basis of the preferential atomic ordering observed in the ternary compounds. Based on the results of magnetic structure refinements using the Rietveld profiling method, antiferromagnetic, noncollinear structures are proposed for these two compounds.

A Mössbauer effect study of the structural and magnetic properties of Y2(Fe1−xAlx)14B

The crystallographic and magnetic properties of Y2(Fe1−xAlx) 14B, where x equals 0.00, 0.02, 0.04, 0.06, and 0.08, have been investigated by Mossbauer spectroscopy and magnetic measurements at room temperature and 85 K. Magnetic anisotropy and magnetization changes with aluminum substitution indicate that, because of size, the aluminum preferentially occupies the j2 site over the remaining five crystallographically nonequivalent iron sites. This preferential occupation has been confirmed by Mossbauer spectral studies, which indicate that the compositional variation of the hyperfine field for each site is related to the number of near‐neighbor aluminum atoms for the site. This compositional variation is helpful in assigning the different spectral components in these alloys as well as in the related Nd2(Fe1−xCox)14B and Y2(Fe1−xCox)14B alloys. In all cases these assignments are consistent with the local symmetry and coordination environment for each site.

Magnetic properties of substituted R 2 (Fe, Al, Co) 14 B compounds

The effects of the substitution of Fe by Al in R 2 (Fe 1-x Al x ) 14 B compounds (R = Y, rare earths) on their magnetic properties have been investigated. The compounds crystallize in the tetragonal structure, P4 2 / mnm, provided x 1 , and the anisotropy field, H A , exhibit a maximum at x = 0.06. The substitution of Fe with Al atoms is also effective in enhancing the coercivity of magnets based on the Nd-Fe-B compounds. As the Y atom carries no magnetic moment, the increased anisotropy field must result from preferential ordering of the non-magnetic Al atoms among the six non-equivalent crystallographic sites of the iron sublattice. Earlier work has shown that the replacement of Fe by Co results in increasing the Curie temperature and decreasing the coercive field. The present data show that the Nd-(Fe, Al,Co)-B magnets have both high Curie temperatures and high coercive forces. Accordingly, it appears that it is possible to improve the thermal properties and reduce the total losses of Nd-Fe-B magnets by appropriate substitution of Fe with Al and Co atoms.

A Mössbauer effect study of the magnetic properties of Nd2(Fe1−xCox)14B and Y2(Fe1−xCox)14B

The atomic and magnetic structures of Nd2(Fe1−xCox)14B, with x equal to 0.0, 0.1, 0.2, and 0.3, and Y2(Fe1−xCox)14B, with x equal to 0.0, 0.1, 0.2, 0.3, and 0.4, have been investigated by Mossbauer spectroscopy at room temperature and 85 K. A Mossbauer effect spectral component analysis, based on neutron diffraction site populations in Nd2(Fe1−xCox)14B, has revealed a stronger compositional dependence for the hyperfine field and magnetic moment on the j2 site than is observed for the other five iron sites. A similar analysis for the Y2(Fe1−xCox)14B compounds shows lower hyperfine fields and hence moments on the c and e sites, as well as a significant decrease in the hyperfine field at the j1 site as the cobalt concentration is increased. The iron site hyperfine fields, and their dependence on cobalt content, are consistent with the local site coordination environments in both series of compounds.

Magnetocrystalline anisotropy of (Nd1−xSmx)2Fe14B and (Nd1−xPrx)2Fe14B

A spin reorientation appears at 140 K in Nd2Fe14B. In order to investigate the magnetic behavior of the rare earth sublattice, the magnetocrystalline anisotropy of (Nd1-xSmx)2Fe14B and (Nd1-xPrx)2Fe14B has been studied by X-ray and magnetic measurements. We find that the substitution of Nd with Sm results in an increasing spin reorientation temperature. A change in easy magnetization direction from the c-axis toward the basal plane is observed at room temperature in (Nd1-xSmx)2Fe14B compounds by increasing the Sm content, x. The effect of substitution of Nd withPr is reversed.

Thermal expansion anomalies of R2(Fe1−x Mx)14B

Thermal expansion anomalies of R2(Fe1−xMx)14B (R=Nd and Y; M=Co and Al) have been observed with x‐ray powder diffraction in the range from room temperature to 1000 K. All these compounds show an abnormal thermal expansion below the Curie temperature. The substitution effect of Fe by Co and Al on the thermal expansion behavior has been investigated to determine how atomic ordering of these substituent atoms influence the Fe‐Fe exchange interactions so as to alter the magnetic properties of the R‐Fe‐B intermetallic compounds.

Structural and magnetic properties of Y(Al1−xFex)12

In order to investigate the magnetic behavior of 3d atoms in the ThMn12‐type structure, the structured and magnetic properties of Y(Al1−xFex)12 were studied by Mossbauer spectroscopy and magnetization measurements. The Y(Al1−xFex)12 intermetallic compounds crystallize in the ThMn12‐type structure for x in the range of 0.3–0.5. The results can be explained on the basis of the preferential atomic ordering observed in the ternary compounds. The compounds are ferromagnetic with Curie temperatures of 130, 170, and 280 K, respectively, for x values of 0.3, 0.4, and 0.5.

Atomic and magnetic structure of Er(Fe1−xNix)3 intermetallic compounds

Neutron diffraction studies have been made on the intermetallic compounds, ErFe2Ni, ErFe1.5Ni1.5, and ErFeNi2, to determine the effect of the nonmagnetic Ni atoms on the three magnetic phases of ErFe3. Diffraction patterns above the Curie temperature show that Ni atoms almost exclusively occupy the h1 sites. At room temperature, a nearly basal plane ferrimagnetic arrangement of magnetic moments results whereas at 4.2 K, a noncollinear structure is observed, in contrast to the uniaxial collinear structure obtained for ErFe3. The results are explained on the basis of the competitive local anisotropies and the change in exchange interactions of Er‐Fe upon substitution of Ni.

The temperature dependence of the Mössbauer hyperfine parameters in Nd2Fe14B

We have determined the temperature dependence of the internal hyperfine field, isomer shift, and quadrupole shift at each of the six iron sites in Nd2Fe14B. The hyperfine parameters are consistent with the local iron site environments. The quadrupole and isomer shifts and their temperature dependences support our assignments of the relative ordering of the internal hyperfine fields as j2>k2>c≊k1>j1>c. We obtain a Mössbauer temperature of 390 K for Nd2Fe14B, which compares well with the Debye temperature of 420K for pure iron.

Neutron diffraction study of Y2(Fe1−xCox)14B (abstract)

The crystallographic and magnetic properties of Y2(Fe1−xCox)14B, x=0.00, 0.1, 0.2, 0.3, 0.4, and 0.5, were investigated by neutron diffraction and magnetic measurements at selected temperatures from 4.2 K to above the Curie temperature. The preferential occupation by Co atoms among the six nonequivalent crystallographic sites of Fe has been determined together with the mean magnetic moments of the Fe and Co atoms. The Fe atoms are found to favor the j2 site. The atomic ordering and its relationship to the magnetic properties are explained on the basis of the local site symmetries and the effect of the differing electronic behavior of the Fe and Co atoms with respect to their nearest neighbors.