Critical behavior and magnetocaloric effect of Mn4.75Ge3(Co, Fe)(0.25) alloys

Abstract

The critical behavior and magnetocaloric effect of Mn5Ge3, Mn4.75Co0.25Ge3 and Mn4.75Fe0.25Ge3 were investigated. The critical exponents of beta = 0.368 and gamma = 1.312 for Mn5Ge3 were in good agreement with the values predicted by the 3D Heisenberg model whereas for Mn4.75Co0.25Ge3 (beta = 0.379, gamma = 1.037) and Mn4.75Fe0.25Ge3 (beta = 0.365, gamma = 1.055) there a large deviation for the gamma values from the Heisenberg model. Curie temperatures and magnetic entropy, Delta S-M, however, were in accordance with the beta values of the three alloys. The respective peak Delta S-M for Mn5Ge3, Mn4.75Co0.25Ge3 and Mn4.75Fe0.25Ge3 was 4.96, 4.67, and 5.11 J/ kg K under an external field change of 3 T. The Delta S-M - T curves for the three alloys collapsed onto a single master curve regardless of the composition and the applied field. It was also demonstrated that the universal behavior with the critical exponents can be used to extrapolate the Delta S-M - T curve to fields experimentally unavailable. (C) 2016 Elsevier B.V. All rights reserved.