Giant magnetocaloric effect induced by reemergence of magnetostructural coupling in Si-doped Mn0.95CoGe compounds

Abstract

It has been reported that the martensitic structural transformation temperature (Tstr) can be lowered and even depressed by Mn vacancy in MnCoGe-based alloys. In the present work, the structural transformation is tuned to reappear and the Tstr increases significantly by substituting Si for Ge in Mn0.95CoGe system, and thus the magnetostructural transition from paramagnetic Ni2In-type phase to ferromagnetic TiNiSi-type phase is again realized around room temperature. Meanwhile, the working temperature window is enhanced to be 22% wider than that of Mn1−xCoGe system. The history-dependent phase transitions have been discussed by measuring the M-H curves in different processes. Mn0.95CoGe0.9Si0.1 experiences a forward martensitic transition in loop process, and then a field-induced metamagnetic transition (FIMT) with large magnetic hysteresis can be observed around Tstrcooling. On the other hand, a reverse martensitic transition is observed in standard process, and the FIMT is depressed by thermal disturbance at higher temperatures. Large MCE is obtained due to the reemergence of magnetostructural transition, e.g., the maximum −ΔSM is 15.0J/kgK for a relatively low field change of 2T, which is larger than those of Mn1−xCoGe system and some other typical magnetocaloric materials in similar temperature range. The comprehensive advantages including giant low-field MCE, wide working temperature range, and lower cost of Si than Ge, suggest that Mn0.95CoGe1−xSix compounds could be promising materials for room temperature magnetic refrigeration.