Effect of static and dynamic disorder on electronic transport inRCo2compounds:Ho(Al

Abstract

We present experimental results on thermoelectric power ͑S͒ and electrical resistivity ͑͒ of pseudobinary alloys Ho͑Al x Co 1−x ͒ 2 ͑0 Յ x Յ 0.1͒, in the temperature range 4.2 to 300 K. The work focuses on the effects of static ͑induced by alloying͒ and dynamic ͑induced by temperature͒ disorder on the magnetic state and electronic transport in a metallic system with itinerant metamagnetic instability. Spatial fluctuations of the local magnetic susceptibility in the alloys lead to the development of a partially-ordered magnetic ground state of the itinerant 3d electron system. This results in a strong increase of the residual resistivity and a suppression of the temperature-dependent resistivity. Thermopower exhibits a complex temperature variation in both the magnetically ordered and in the paramagnetic state. This complex temperature variation is attributed to the electronic density-of-states features in vicinity of Fermi energy and to the interplay of magnetic and impurity scattering.Our results indicate that the magnetic enhancement of the Co 3d band in RCo 2 -based alloys upon a substitution of Co by nonmagnetic elements is mainly related to a progressive localization of the Co 3d electrons caused by disorder. We show that the magnitude of the resistivity jump at the Curie temperature for RCo 2 compounds exhibiting a first-order phase transition is a nonmonotonic function of the Curie temperature due to a saturation of the 3d-band spin-fluctuation magnitude at high temperatures.HoCo 2 belongs to the family of intermetallic RCo 2 cubic Laves phases ͑R stands for rare-earth elements͒ which are well known for their outstanding magnetic properties associated with itinerant 3d electron subsystem. 1-3 Long-range magnetic order of the 3d electron subsystem of paramagnetic YCo 2 and LuCo 2 can be induced by external magnetic field exceeding a certain critical value B c . This critical field was found to be about 70 T for YCo 2 ͑Ref. 4͒ and about 77 T for LuCo 2 . 5 Partial replacement of cobalt by aluminum leads to a decrease of B c and to the appearance of weak itinerant ferromagnetism in Y͑Al x Co 1−x ͒ 2 for x Ͼ 0.12. 6,7 In the case of magnetic RCo 2 compounds, long-range magnetic order of the 3d electron subsystem is induced by ordering of the localized magnetic moments of the rare earths. A substitution of Al on Co sites of the magnetic RCo 2 compounds, results in a considerable increase of the Curie temperature. 8 This behavior was interpreted within the framework of the itinerant magnetism by an increase of the density of states ͑DOS͒ at the Fermi level as Co is replaced by Al. However, the mechanism, responsible for the increase of DOS at the Fermi level, remains obscure. Mainly two scenarios have been proposed: in the first, DOS increases due to depopulation of 3d-Co band when Co is replaced by Al 6,9 ; in the second, the DOS increase is caused by a narrowing of the 3d band due to an expansion of the crystal lattice in the alloys. 7,10 In the present work, we use the temperature-dependent thermopower S͑T͒ t...

Magnetic ordering in the fine particles of some bulk Pauli paramagnets

“…It is possible that the observed magnetic transition in the fine-particles of the present materials is controlled by electronic structure [7]. In fact, the narrowing of the d-band due to defects and subsequent shift of the d states to Fermi energy has been proposed to play a crucial role favoring itinerant electron magnetism in the chemically-doped RCo 2 [17]. It is possible that such factors under favorable conditions stabilize, rather than destabilizing, magnetic ordering in fine-particles prepared by ball-milling.…”

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

“…This raises a question whether the electronic structure changes following reduced dimension and/or defects play a role in deciding the magnetic characteristics of milled specimens. At this juncture, it may be recalled that the role of defects on altering electronic density of states (and hence magnetism) was addressed in the case of binary Laves phase compounds [17] and therefore a role of such a factor in ball-milled specimens can not be ruled out.…”

Magnetic disordered in Ti doped ErCo2 alloys: Griffiths-like behavior

“…Many previous investigations of RCo 2 and RCo 2 À x T x (where T represents a transition metal) using different techniques [1,2,21] have made clear that Co moments appear at T c under the influence of the molecular field of the rare earth sublattice. However, the type of ordering for the Co moments remains obscure.…”