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Electronic structure of rare earth magnets and tungsten-based transition metal alloys by photoelectron spectroscopy
Abstract
Photoelectron spectroscopy was used to investigate the electronic and magnetic structures of crystalline rare earth magnetic materials of the form R$\sb2$Fe$\sb{14}$B with R = Y, Nd, and Gd. Measurements are reported for photon energies of 21.2 eV, 40.8 eV, 100 eV and 130 eV. The major features of the spectra include an Fe(3d) band centered at E$\sb{\rm B}$ = $-$0.7 eV, Gd(4f) at $-$8.8 eV, Nd(4f) at $-$5.3 eV, and B(2s) at $-$8.6 eV. These results compare favorably with self-consistent, semi-relativistic, spin-polarized linear-muffin-tin-orbital calculations of Jaswal for Y$\sb2$Fe$\sb{14}$B. Measurements were made in both the ferromagnetic state (T = 296 K) and paramagnetic state (T = 623 K). No change in the photoelectron intensity was detected on heating above the Curie point T$\sb{\rm C}$ = 585 K. This constancy of the electronic density of states indicates a paramagnetic state with considerable magnetic short-range order, as in the fluctuating band model of itinerant ferromagnetism. In addition, binary transition metal alloys of the form T$\sb{\rm x}$W$\sb{\rm 100-x}$ where T = Cu, Ni, and Co are investigated by photoelectron spectroscopy, x-ray diffraction, and x-ray fluorescence. For each series, seven to nine x compositions were produced by sputtering. X-ray diffraction measurements show amorphous phases occurring from 52 $<$ x $<$ 65 for Cu$\sb{\rm x}$W$\sb{\rm 100-x}$, 30 $<$ x $<$ 50 for Ni$\sb{\rm x}$W$\sb{\rm 100-x}$, and 15 $<$ x $<$ 80 for Co$\sb{\rm x}$W$\sb{\rm 100-x}$. Photoelectron spectra are presented for photon energies of 21.2 eV and 40.8 eV. Spectra for the CuW series show that the Cu d-band peak (E$\sb{\rm B}$ = $-2.2$ eV) in pure Cu shifts to E$\sb{\rm B}$ = $-$2.9 eV upon alloying to Cu$\sb{81}$W$\sb{19}$. Measurements for the NiW and CoW series exhibit a smaller d-band peak shift of approximately 0.3 eV away from e$\sb{\rm F}$ as the composition changes to pure tungsten. The alloys appear to fit the split-band model which is described with the coherent potential approximation.
Subject Area
Condensation
Recommended Citation
Engelhardt, Michael Anthony, "Electronic structure of rare earth magnets and tungsten-based transition metal alloys by photoelectron spectroscopy" (1988). ETD collection for University of Nebraska-Lincoln. AAI8818617.
https://digitalcommons.unl.edu/dissertations/AAI8818617