Vacancy-tuned paramagnetic/ferromagnetic martensitic transformation in Mn-poor Mn_{1-x}CoGe alloys

TL;DR

This study demonstrates that vacancy engineering in Mn-poor Mn_{1-x}CoGe alloys enables a temperature window for martensitic transformation near room temperature, leading to magnetic-field-induced effects and large magnetocaloric responses.

Contribution

It introduces a vacancy-tuning strategy to control martensitic transformation temperatures and magnetic properties in Mn_{1-x}CoGe alloys, a novel approach in this material system.

Findings

Vacancy tuning shifts transformation temperature near room temperature.

Large magnetization difference enables magnetic-field-induced transformation.

Reduced thermal hysteresis improves material stability.

Abstract

It is shown that a temperature window between the Curie temperatures of martensite and austenite phases around the room temperature can be obtained by a vacancy-tuning strategy in Mn-poor Mn1-xCoGe alloys (0 <= x <= 0.050). Based on this, a martensitic transformation from paramagnetic austenite to ferromagnetic martensite with a large magnetization difference can be realized in this window. This gives rise to a magnetic-field-induced martensitic transformation and a large magnetocaloric effect in the Mn1-xCoGe system. The decrease of the transformation temperature and of the thermal hysteresis of the transformation, as well as the stable Curie temperatures of martensite and austenite, are discussed on the basis of the Mn-poor Co-vacancy structure and the corresponding valence-electron concentration.