Emergent properties in the natural composite Ni2MnSb0.5Al0.5

Abstract

We have investigated the structure, transport and magnetic properties of Ni2MnSb0.5Al0.5 Heusler alloy. Structural analysis using x-ray diffraction and scanning electron microscopy has confirmed Ni2MnSb0.5Al0.5 to be a natural composite of Ni2MnSb and Ni2MnAl phases, regardless of annealing conditions. This composite has a dendritic microstructure formed by the phase separation during solidification. The electronic phase separation was confirmed using x-ray near edge absorption spectroscopy, recorded at Mn and Ni K-edge and supported by ab-initio calculations of the same using multiple scattering theory. A thorough characterization of this novel composite form of Ni2MnSb0.5Al0.5 Heusler alloy has been carried out by recording its magnetic and transport properties including electrical resistivity, thermal conductivity, and heat capacity. The composite micro-structure of this system plays a crucial role in drastically reducing its thermal conductivity value, while maintaining its metallic character. Unlike many oxide composites, the magnetic properties of the Ni2MnSb0.5Al0.5 cannot be considered as the volume average of the characteristics of the two phases, rather it shows a long range ferromagnetic order with Curie temperature of 334 K and magnetic moment of 2.52 /f.u.