Martensitic transformation and magnetocaloric effect of Mn<sub>1−</sub><sub><italic>x</italic></sub>Bi<sub><italic>x</italic></sub>CoGe alloys

Abstract

<p indent="0mm">Quaternary alloys of MnCoGe with the partial addition of other elements can realize coupling between structural and magnetic transformations, and it can present apparent magnetocaloric effects during martensitic transformation. In this paper, we have prepared Mn₁₋_{<italic>x</italic>}Bi_{<italic>x</italic>}CoGe (<italic>x</italic>=0, 0.03, 0.04, 0.05, 0.055, 0.06) series alloys using arc melting in a protective argon atmosphere. Experimental results indicate that the structural transformation temperature (<italic>T</italic>_M) of the samples shifts to low temperatures with increasing elemental Bi doping. The Mn_0.945Bi_0.055CoGe alloy (valence electron concentration<italic>e</italic>/<italic>a</italic>=6.63) undergoes a first-order magnetostructural transition (FOMST) near room temperature, and a large magnetic entropy change of <sc>36.8 J kg⁻¹ K⁻¹</sc> is obtained under an external magnetic field of <sc>0–5 T,</sc> which proves that elemental Bi doping in MnCoGe alloys can effectively tune the martensitic transformation temperature and further improve the magnetic entropy change.