Magnetism of fine particles of Kondo lattices, obtained by high-energy ball-milling

Abstract

Despite intense research in the field of strongly correlated electron behavior for the past few decades, there has been very little effort to understand this phenomenon in nanoparticles of the Kondo lattices. In this paper, we review the results of our investigation on the fine particles (<<1 μm) of some of the alloys obtained by high-energy ball-milling, to bring out that this synthetic method paves a way to study strong electron correlations in nanocrystals of such alloys. We primarily focus on the alloys of the series CeRu(2 - x)Rh(x)Si2, lying at different positions in Doniach's magnetic phase diagram. While CeRu2Si2, a bulk paramagnet, appears to become magnetic (of a glassy type) below about 8 K in fine particle form, in CeRh2Si2, an antiferromagnet (T(N) = 36 K) in bulk form, magnetism is destroyed (at least down to 0.5 K) in fine particles. In the alloy CeRu0.8Rh1.2Si2, at the quantum critical point known to exhibit non-Fermi liquid behavior in the bulk form, no long range magnetic ordering is found.

Magnetism mediated by a majority of [Fe3+ + $\mathbf{V}_{\mathbf{O}}^{\mathbf{2-}}$ ] complexes in Fe-doped CeO2nanoparticles

“…XPS studies of CeO 2 nanoparticles [26] reported the coexistence of Ce 3+ ions with Ce 4+ ions and greater reduction of Ce 3+ ions with decreasing particle size. Extensive studies on the electronic structure of Ce compounds by theoretical (Kondo systems) models [27,28] identified that lowest energy (4 f 0 ) and the first excited (4 f 1 ) configurations are well separated in energy and Ce ions retain a mainly Ce 3+ (4 f 1 ) configuration at the surface [29,30]. Thus, it would be expected that nanoscale CeO 2 would lead to a more 4 f localized behaviour (Ce 3+ valance favoured) at the surface with the decrease in size, an effect scaling with the surface-to-volume ratio.…”

Contrasting magnetic behavior of fine particles of some Kondo lattices

“…In the field of strongly correlated electron systems (SCES) containing 4f and 5f metals, the question of how the properties get modified when the particle size is reduced to micron or nano scale has not been sufficiently addressed in the literature. In this respect, we have initiated some work in recent years [1,2] by synthesizing fine particles by high-energy ball-milling [3] in an atmosphere of toluene. It was noticed that CeRu 2 Si 2 , one of the most celebrated non-magnetic Kondo lattices in the bulk form, crystallizing in ThCr 2 Si 2 -type tetragonal structure, reveals features due to magnetic ordering around (T N =) 8 K when the particle size is reduced, whereas isostructural CeRh 2 Si 2 , known to exhibit antiferromagnetic order near 36 K, loses magnetism.…”