Structure and magnetic order of the Heusler compoundCo2NbSn

Abstract

We present a detailed study of the structural and magnetic phase transitions of the Heusler compound Co 2 NbSn. This material undergoes a structural transition at T S ϭ235 K from the cubic Heusler Fm3m hightemperature phase into an orthorhombic low-temperature lattice of Pmma symmetry. Further, the system exhibits a magnetic transition at T C ϭ116 K from para-to ferromagnetism. While on a macro-and mesoscopic scale Co 2 NbSn appears to be fully Fm3m ordered, from microscopic studies we find that on an atomic scale site disorder is present. We discuss the implications of these findings for the anomalous macroscopic physical properties and domain formation in the ferromagnetic state in Co 2 NbSn.

X-ray magnetic circular dichroism in d and f ferromagnetic materials: recent theoretical progress. Part I (Review Article)

“…184,185 Further, at the first-order transition, T s , the accompanying specific heat anomaly is smeared out over a wide temperature range of 60 K. Such behavior points to the presence of crystallographic disorder, which has been identified recently by means of a detailed microscopic study of the local crystallographic site symmetry in Ref. 182. Co 2 NbSn is disordered on an atomic scale, i.e., there are random displacements of Co, Nb, and Sn ions from their nominal positions in both the Fm3m and Pmma lattices.…”

“…However, unlike Ni 2 MnGa, for which the martensitic phase transition ͑T s = 200 K͒ occurs within the ferromagnetically ordered phase ͑T c = 376 K͒, for Co 2 NbSn the martensitic phase transition temperature T s = 233 K is well above the ferromagnetic ordering temperature of T c = 116 K. 182 Consequently, the shape memory behavior in Co 2 NbSn cannot be controlled by a magnetic field.…”

“…One should mention that although the energy band structure of the low-temperature phase of Co 2 NbSn was evaluated in Ref. 186 as tetragonal, recent structural investigations 182 show that the low-temperature phase of this compound has orthorhombic Pmma symmetry.…”

“…51͒. 182 Two inequivalent Co ions occupy the 4h ͑x =0, y = 0.253, z =1/ 2͒ and 4k ͑x =1/ 4, y = 0.746, z = 0.051͒ Wyckoff positions. The Nb ions occupy also two inequivalent Wyckoff positions 2a ͑x =0, y =0, z =0͒ and 2f ͑x =1/ 4, y =1/ 2, z = 0.527͒.…”

Superconductivity in the Heusler alloy Pd2YbPb

“…7), which seems to be reasonable when compared with those of isoelectronic similar compounds. Wolter et al [16] have recently obtained, by means of heat capacity measurements, the value of T D for the Heusler compound Co 2 NbSn to be 365 K. As well known, the meansquare displacement of atoms can be expressed [17] as…”