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

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.