Giant Magneto-Volume and Magneto-Caloric Effects of Frustrated Antiferromagnet Mn₃GaN under Hydrostatic Pressure

Abstract

Volumetric and caloric effects associated with magnetic transition have been investigated systematically for a series of manganese nitrides based on Mn3GaN. The antiferromagnetic transition temperature TN of Mn3GaN, which is known for its giant barocaloric effect, was controlled at 220–390 K using elemental substitution or nitrogen deficiency while maintaining a steep transition and a large calorific effect. For nitrogen-deficient Mn3GaN0.87, TN decreases continuously at a constant rate with pressure up to 900 MPa. However, both volume and entropy changes (ΔV and ΔS) are retained up to 300 MPa. Beyond that, ΔS decreases concomitantly with increasing pressure, although no decrease in ΔV can be confirmed. The measured TN seems to deviate from the Clausius–Clapeyron relation, which might be related to the anomalous pressure dependence of ΔV and ΔS. These findings suggest that a phase other than the cubic Γ5g antiferromagnetic phase, which is stable at ambient pressure, appears at high pressure. Such anomalous magnetic properties might be attributable to the complex bond length dependence of the magnetic interaction.