Abstract
Measurements of specific heat, dc magnetic susceptibility, and Yb ${L}_{\text{II}}$ and ${L}_{\text{III}}$ x-ray absorption near-edge structure (XANES) and extended x-ray absorption fine structure (EXAFS) on ${\text{YbAl}}_{3}$ milled alloys are reported. X-ray diffraction patterns are consistent with a reduction in particle size down to 10 nm and an increase in the lattice strain up to 0.4% for 120 h of milling time. A decrease in the mean valence from 2.86 for the unmilled alloy to 2.70 for 120 h milled ${\text{YbAl}}_{3}$ is obtained from the analysis of XANES spectra. From the analysis of spectra in the EXAFS region, an increase in the mean-square disorder of neighbor distance with milling time is detected in good agreement with the results of x-ray diffraction. Size effects strongly influence the magnetic and thermal properties. The value for the maximum of the magnetic susceptibility decreases around 30% for 120 h milled alloy and an excess specific heat, with a peak around 40 K in the milled samples, is derived. These changes in the physical properties along the milled ${\text{YbAl}}_{3}$ alloys are associated with the reduction in particle size. Such a reduction leads to the existence of a large number of ${\text{Yb}}^{2+}$ atoms at the surface with respect to the bulk affecting the overall electronic state.
Highlights
Magnetic fine particle systems are subject of interest attracting much scientific activities today because of the variety of interesting phenomena arising from the existence of nanometric structures.1,2 Within this area of research, the vast majority of the studies have been devoted to systems comprising transition metals.3 little attention has been paid to nanocrystalline rare-earth intermetallics
The Rietveld refinement of the x-ray diffraction data shows a decrease in the particle size down to nm and an increase in the lattice strain up to 0.4% for 120 h of milling time
In order to provide a microscopic point of view for the origin of the observed presence of an Yb2+ contribution in the magnetic susceptibility and the existence of an excess specific-heat stemming from interfacial atoms, we present the results on the electronic properties and the short-range structure as sampled by x-ray absorption measurements, XANES, and EXAFS
Summary
Magnetic fine particle systems are subject of interest attracting much scientific activities today because of the variety of interesting phenomena arising from the existence of nanometric structures. Within this area of research, the vast majority of the studies have been devoted to systems comprising transition metals. little attention has been paid to nanocrystalline rare-earth intermetallics. Magnetic fine particle systems are subject of interest attracting much scientific activities today because of the variety of interesting phenomena arising from the existence of nanometric structures.. Magnetic fine particle systems are subject of interest attracting much scientific activities today because of the variety of interesting phenomena arising from the existence of nanometric structures.1,2 Within this area of research, the vast majority of the studies have been devoted to systems comprising transition metals.. Several studies have been reported which are related to the GdX2 Laves phases under mechanical milling. In this case, the relationship between the structural and magnetic changes induced by the milling process results in the evolution from a ferromagnetic behavior to a spin-glass phase, which emerges at lower temperatures.. The relationship between the structural and magnetic changes induced by the milling process results in the evolution from a ferromagnetic behavior to a spin-glass phase, which emerges at lower temperatures. More recently, a study of the magnetic properties of TbAl2 milled alloys has revealed that disorder and size effects are important in crucial understanding of the magnetic behavior, with a pronounced variation of coercivity with the grain size.
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