Mössbauer study of permanent-magnet materials: Sm\u3csub\u3e2\u3c/sub\u3eFe\u3csub\u3e17-x\u3c/sub\u3eAl\u3csub\u3ex\u3c/sub\u3e compounds

The Fe57 Mössbauer spectra of Sm2Fe17-xAlx, where x=0, 1.0, 2.0, 3.0, and 4.0, have been measured at room temperature and analyzed. The ternary compounds Sm2Fe17-xAlx have the rhombohedral Th2Zn17 structure. Mössbauer measurements showed that all the compounds studied were ferromagnetic. The average hyperfine field was found to decrease with the increasing aluminum concentration, which is in qualitative agreement with magnetic measurements. The decrease in the average hyperfine field was from 224 kOe at x=0 to 174 kOe at x=4. By fitting the spectra we found that the hyperfine fields for the iron sites decrease in the order 6c, 9d, 18f, and 18h. The measured average isomer shift relative to α-iron was found to increase linearly with x. Analysis of the spectra showed that Al atoms occupy the 6c, 18h, and 18f, but not 9d, Fe sites and the fraction of occupancy of Al was found to depend on x

Photoemission studies of Co- and Fe-based compounds with the ThMn\u3csub\u3e12\u3c/sub\u3e structure

The electronic structures of NdFe11Ti, NdCo10V2, and YCo10Cr2 have been studied with photoemission and spin-polarized calculations. The changes in these electronic structures upon nitrogenation have also been investigated. In the Fe compound, the Fe 3d states dominate the calculated density of states near the Fermi-edge, and the N(2p) peak is evident at around 6.3 eV. There is no shift in Fe 3d peaks visible in these compounds upon nitrogenation. Other than small energy shifts in the peak positions, there is an overall agreement between experimental data and the calculated density of states. The calculated density of states in the local-density approximation for YCo10V2 is broadened to account for the well-known many-body effects and compared with the photoemission data. Journal of Applied Physics is copyrighted by The American Institute of Physics

Mössbauer, magnetic, and electronic-structure studies of YFe\u3csub\u3e12-x\u3c/sub\u3eMo\u3csub\u3ex\u3c/sub\u3e compounds

Mössbauer spectra, magnetization measurements, and self-consistent spin-polarized electronic structures of YFe12-xMox, where x=0.5, 1.0, 2.0, 3.0, and 4.0, are reported. The ternary compounds YFe12-xMox have the crystalline tetragonal ThMn12 structure. Analyses of the Mössbauer spectra show that Mo atoms occupy the 8i Fe sites of the ThMn12 structure, in agreement with previous observations. Room-temperature magnetic and Mössbauer measurements show that the compounds with x≤2.0 are ferromagnetic and with x≥3.0 are paramagnetic. Measurements at 25 K show that all the samples are magnetically ordered. The magnetic hyperfine field is found to decrease with increasing Mo concentration, which is in qualitative agreement with the calculated magnetic moments. The calculated magnetization decreases less rapidly with increasing x than the experimental data. In general the data suggest that with increasing Mo concentration there is an increase of antiferromagnetic coupling among the Fe moments, which leads to cluster-glass or spin-glass-like phenomena. The measured isomer shift relative to α-iron is found to decrease linearly with x

Electronic structures and Curie temperatures of iron-based rare-earth permanent-magnet compounds

The modification of the electronic structures of Sm2Fe17-xAlxNy, NdFe11TiNy, and YFe12-xMox upon alloying and nitriding are examined with self-consistent spin-polarized calculations and soft-x-ray photoemission measurements between 18 and 135 eV. The changes in the Curie temperature Tc with substitutional modifications and nitrogen addition are modeled with self-consistent spin-polarized electronic structure calculations and the spin-fluctuation theory of Mohn and Wohlfarth which relates the electronic structure to Tc. The calculations show that the spin-summed density of states at the Fermi energy is related to Tc. The photoemission spectra are dominated by the Fe 3d electrons within 3 eV of the Fermi energy in agreement with calculations. Changes in the density of states at the Fermi energy for interstitial and and substitutional modification compare well with calculations. Using photoemission results with experimental magnetic moments for the substitutional modification of the compound Sm2Fe17-xAlx, the spin-fluctuation theory predicts a change in Tc in agreement with the measured change in Tc. Spin-resolved photoemission spectra for c-axis oriented Sm2Fe17N2.6 with magnetization perpendicular to the surface are presented and compared to theoretical calculations

Electronic structure and Curie temperature of YFe\u3csub\u3e12-x\u3c/sub\u3eMo\u3csub\u3ex\u3c/sub\u3eN\u3csub\u3e\u3ci\u3ey\u3c/i\u3e\u3c/sub\u3e compounds

The electronic structures of YFe12-xMoxNy , where x=1.0, 2.0 and y=0, 0.7, have been studied with photoemission and spin-polarized calculations. The peak near the Fermi level in the energy distribution curves (EDC) becomes successively broader with larger Mo concentration. The features in the calculated density of state at 1.3 and 2.7 eV are not readily seen in the EDC, and this may be due to lifetime effects in these compounds. Finally, changes in Curie temperature (Tc) with the change of N or Mo concentration are compared with prediction of the theory of Mohn and Wohlfarth. Reasonable agreement is obtained in the N case but not in the Mo case, the latter most likely due to hybridization of Fe and Mo d bands

Electronic structure of Sm\u3csub\u3e2\u3c/sub\u3eFe\u3csub\u3e17\u3c/sub\u3eN\u3csub\u3ex\u3c/sub\u3e compounds

Sm2Fe17Nx is of considerable current interest as a permanent-magnet material because of its enhanced Curie temperature and uniaxial anisotropy. The electronic structures of Sm2Fe17Nx for x=0 and x~2.6 have been studied with photoemission and spin-polarized calculations. The materials are prepared by arc melting and nitrogen is introduced by ion implantation. The nitrogen concentration is quantified with Auger electron spectroscopy. The Sm 4f electrons with binding energies between 6 and 10 eV are investigated with resonant photoemission using photon energies near 140 eV. The major features of ultra-violet photoemission spectra include the Fe 3d band with a strong peak at 0.8 eV and a small peak at 2.9 eV below the Fermi energy which agree quite well with the theoretical density of states calculation. The modification of the electronic structure with nitrogen concentration is studied to understand the effect of nitrogen addition on the magnetic properties. Journal of Applied Physics is copyrighted by The American Institute of Physics