# First order magneto-structural transition and magnetocaloric effect in MnNiGe$_{0.9}$Ga$_{0.1}$

## TL;DR

This study investigates the magneto-structural transition and magnetocaloric effect in MnNiGe$_{0.9}$Ga$_{0.1}$, revealing phase coexistence, non-equilibrium magnetic states, and significant cooling performance near 95 K.

## Contribution

It reports the first detailed analysis of the magneto-structural transition and magnetocaloric properties in MnNiGe$_{0.9}$Ga$_{0.1}$, highlighting phase coexistence and field-dependent effects.

## Key findings

- Incomplete transition with phase coexistence at low temperatures.
- Large inverse magnetocaloric effect across the transition.
- High relative cooling power compared to similar alloys.

## Abstract

The first order magneto-structural transition ($T_t\simeq95$ K) and magnetocaloric effect in MnNiGe$_{0.9}$Ga$_{0.1}$ are studied via powder x-ray diffraction and magnetization measurements. Temperature dependent x-ray diffraction measurements reveal that the magneto-structural transition remains incomplete down to 23 K, resulting in a coexistence of antiferromagnetic and ferromagnetic phases at low temperatures. The fraction of the high temperature Ni$_2$In-type hexagonal ferromagnetic and low temperature TiNiSi-type orthorhombic antiferromagnetic phases is estimated to be $\sim 40\%$ and $\sim 60\%$, respectively at 23 K. The ferromagnetic phase fraction increases with increasing field which is found to be in non-equilibrium state and gives rise to a weak re-entrant transition while warming under field-cooled condition. It shows a large inverse magnetocaloric effect across the magneto-structural transition and a conventional magnetocaloric effect across the second order paramagnetic to ferromagnetic transition. The relative cooling power which characterizes the performance of a magnetic refrigerant material is found to be reasonably high compared to the other reported magnetocaloric alloys.