Influence of intermartensitic transitions on transport properties of Ni2.16Mn0.84Ga alloy

TL;DR

This study investigates how intermartensitic transitions in Ni2.16Mn0.84Ga alloy significantly influence its magnetic and transport properties, especially resistivity, due to changes in martensitic modulation and Fermi surface nesting.

Contribution

It reveals the impact of intermartensitic transitions on transport and magnetic properties, highlighting the role of Fermi surface nesting in resistivity differences between martensitic phases.

Findings

Large resistivity difference (~15%) between 5M and 7M martensites.

Intermartensitic transition causes significant thermal hysteresis in resistivity and magnetization.

Fermi surface nesting may explain the resistivity behavior at martensitic transitions.

Abstract

Magnetic, transport, and x-ray diffraction measurements of ferromagnetic shape memory alloy Ni$_{2.16}$Mn$_{0.84}$Ga revealed that this alloy undergoes an intermartensitic transition upon cooling, whereas no such a transition is observed upon subsequent heating. The difference in the modulation of the martensite forming upon cooling from the high-temperature austenitic state [5-layered (5M) martensite], and the martensite forming upon the intermartensitic transition [7-layered (7M) martensite] strongly affects the magnetic and transport properties of the alloy and results in a large thermal hysteresis of the resistivity $\rho$ and magnetization $M$. The intermartensitic transition has an especially marked influence on the transport properties, as is evident from a large difference in the resistivity of the 5M and 7M martensite, $(\rho_{\mathrm{5M}} - \rho_{\mathrm{7M}})/\rho _{\mathrm{5M}} \approx 15%$, which is larger than the jump of resistivity at the martensitic transition from the cubic austenitic phase to the monoclinic 5M martensitic phase. We assume that this significant difference in $\rho$ between the martensitic phases is accounted for by nesting features of the Fermi surface. It is also suggested that the nesting hypothesis can explain the uncommon behavior of the resistivity at the martensitic transition, observed in stoichiometric and near-stoichiometric Ni-Mn-Ga alloys.