Formation and magnetic properties of spark plasma sintered Mn$_{3-\delta}$ ($\delta$ = 0, 1) alloys

TL;DR

This study synthesizes Mn$_{3- ext{δ}}$Ga alloys via Spark Plasma Sintering, revealing their magnetic properties, phase coexistence, and theoretical insights into their structure and magnetization mechanisms.

Contribution

It provides new synthesis and characterization of Mn$_{3- ext{δ}}$Ga alloys, combining experimental magnetic measurements with DFT calculations to understand their phase stability and magnetic behavior.

Findings

Mn$_3$Ga is single-phase with high Curie temperature (~780 K).

Mn$_2$Ga coexists with Mn$_9$Ga$_5$ phase due to lower formation energy.

Alloys exhibit hard magnetic behavior with significant room temperature magnetization.

Abstract

We present the synthesis of D0$_{22}$ Mn$_{3 - \delta}$Ga ($\delta$ = 0, 1) Heusler alloys by Spark Plasma Sintering method. The single phase Mn$_3$Ga (T$_\mathrm{c}$ $\simeq$ 780 K) is synthesized, while Mn$_2$Ga (T$_\mathrm{c}$ $\simeq$ 710 K) is found to coexist with a near-stoichiometric room temperature paramagnetic Mn$_9$Ga$_5$~($\approx$ 15 \%) phase due to its lower formation energy, as confirmed from our density functional theory (DFT) calculations. The alloys show hard magnetic behavior with large room temperature spontaneous magnetization m$_s$(80 kOe) = 1.63 (0.83) $\mu_\mathrm{B}$/f.u. and coercivity H$_\mathrm{c}$ = 4.28 (3.35) kOe for Mn$_3$Ga (Mn$_2$Ga). The magnetic properties are further investigated till T$_\mathrm{c}$ and the H$_\mathrm{c}$ (T) analysis by Stoner-Wohlfarth model shows the nucleation mechanism for the magnetization reversal. The experimental results are well supported by DFT calculations, which reveal that the ground state of D0$_{22}$ Mn$_2$Ga is achieved by the removal of Mn-atoms from full Heusler Mn$_3$Ga structure in accordance with half Heusler alloy picture.