Onset of itinerant ferromagnetism associated with semiconductor-metal transition in Ti x Nb1 − x CoSn half Heusler solid solution compounds

Abstract

In this paper, the magnetic and transport properties of the TixNb1−xCoSn solid solution compounds with half Heusler cubic MgAgAs-type structure have been studied. This work shows the onset of ferromagnetism associated with a semiconductor to metal transition. The transition occurs directly from ferromagnetic metal to semiconducting state as it is the case in the TiCoxNi1−xSn series studied previously. A weak quantity of Ti in NbCoSn is sufficient to allow the appearance of ferromagnetic order and metallic state. The variations of the Curie temperature as a function of saturation and effective paramagnetic moments are related to the itinerant ferromagnetism model. A comparison is made with the TiCoSnxSb1−x series (also studied previously), where the transition from TiCoSn ferromagnetic metal to non-magnetic semiconductor TiCoSb occurs through an intermediate metallic Pauli-like state.

A new n-type half-Heusler thermoelectric material NbCoSb

“…Besides MNiSn and MCoSb (M = Hf, Zr and Ti), other HH thermoelectric materials with 18 VEC such as NbCoSn (ZT = 0.3 at 850 K for Nb 0.99 Ti 0.01 CoSn 0.9 Sb 0.1 ) [23,24], VFeSb (ZT = 0.25 at 550 K for pure VFeSb) [25,26] and so on, were also investigated in recent years. However, there is very little work on forming HH phase material using elements with more or less than 18 VEC for TE application.…”

Half-Heusler Structures with Full-Heusler Counterparts: Machine-Learning Predictions and Experimental Validation

“…Although disorder could be viewed as a nuisance, it offers a powerful tool to control physical properties, because small amounts of disorder can have profound effects on the electronic structure and on the performance of magnetic, magnetocaloric, or thermoelectric materials. For example, substituting Ti for Nb in Ti x Nb 1– x CoSn causes transitions from a nonmagnetic semiconductor to a ferromagnetic metal, and self-doping with Ni in ZrNiSn improves thermoelectric properties by reducing thermal conductivity by over 60% . Another type of disorder, though less commonly reported, arises from vacancy defects.…”