Spin-valve nature and giant coercivity of a ferrimagnetic spin semimetal Mn$_2$IrGa

TL;DR

This study identifies Mn$_2$IrGa as a spin semimetal with giant coercivity and spin-valve features, supported by experimental and theoretical evidence, indicating its potential for spintronic applications.

Contribution

The paper reports Mn$_2$IrGa as a new spin semimetal with unique magnetic and transport properties, including giant coercivity and spin-valve behavior, confirmed through combined experimental and ab-initio calculations.

Findings

Giant coercive field of about 8.5 kOe at 2 K.

Evidence of spin-valve characteristics from asymmetric magnetoresistance.

Confirmation of semimetallic behavior via resistivity and specific heat measurements.

Abstract

Spin semimetals are amongst the most recently discovered new class of spintronic materials, which exhibit a band gap in one spin channel and semimetallic feature in the other, thus facilitating tunable spin transport. Here, we report Mn$_2$IrGa to be a candidate material for spin semimetal along with giant coercivity and spin-valve characteristics using a combined experimental and theoretical study. The alloy crystallizes in an inverse Heusler structure (without any martensitic transition) with a para- to ferri-magnetic transition at $T_\mathrm{C} \sim$ 243 K. It shows a giant coercive field of about 8.5 kOe (at 2 K). The negative temperature coefficient, relatively low magnitude and weak temperture dependance of electrical resistivity suggest the semimetallic character of the alloy. This is further supported by our specific heat measurement. Magnetoresistance (MR) confirms an irreversible nature (with its magnitude $\sim$1\%) along with a change of sign across the magnetic transition indicating the potentiality of Mn$_2$IrGa in magnetic switching applications. In addition, asymmetric nature of MR in the positive and negative field cycles is indicative of spin-valve characteristics. Our ab-initio calculations confirm the inverse Heusler structure with ferrimagnetic ordering to be the lowest energy state, with a saturation magnetization of 2 $\mu_\mathrm{B}$. $<100>$ is found to be the easy magnetic axis with considerable magneto-crystalline anisotropy energy. A large positive Berry flux at/around $\Gamma$ point gives rise to an appreciable anomalous Hall conductivity ($\sim$-180 S/cm).