Widening of working temperature range in Mn5-xCuxGe3 (x = 0.1 and 0.3) magnetocaloric compounds by compositional tuning

Abstract

This study presents the effect of Cu doping on the fundamental properties, magnetocaloric effect, and critical behavior of Mn5Ge3 system. Mn5-xCuxGe3 compounds with x = 0.1 and 0.3 conform D88-hexagonal structure. The unit cell volume decreases, and MnI-MnI distance increases with Cu content. This modifies the exchange interaction and impacts Curie temperature and saturation magnetization accordingly. The critical exponents β and γ of x = 0.1 compound are of 3D Ising class, while the x = 0.3 compound shows non-conventional behavior with its γ lying within the 3D Ising framework and β lying between 3D XY and Heisenberg classes. Both the compounds have extended-type spin interactions, and the decay of the exchange integrals has been calculated. Mn5-xCuxGe3 compounds clearly outperform most materials of Mn5Ge3 class in terms of the magnetocaloric effect. They show an appreciable reversible isothermal entropy change across a wide temperature span with a large relative cooling power near the room temperature effect. These compounds can be combined with other suitable Mn5Ge3 materials and used in ‘active magnetic regenerative (AMR)’ systems as layered refrigerants for more efficient magnetocaloric cooling.