Magnetic and magnetocaloric properties of Ni-doped MnCoGe alloy

In this work, a Ni-doped MnCoGe alloy has been synthesized by doping 4 wt% of Ni in place of Ge. The room temperature XRD pattern shows that the alloy has crystallized in two phases: hexagonal-MnCoGe and cubic-Co2MnGe and in addition, there are vacancies at Co and Ge sites. Around room temperature, MnCoGe phase has hexagonal structure and as the temperature is lowered, the structural transition takes place to orthorhombic-MnCoGe phase. When external magnetic field is low, orthorhombic phase is antiferromagnetic, but as field strength is increased, the ferromagnetic ground state is established. This alloy undergoes a second-order ferromagnetic transition followed by a first-order structural transition in a narrow temperature width. These have synergistically resulted in a single, reversible -ΔS(T)\documentclass[12pt]{minimal} \usepackage{amsmath} \usepackage{wasysym} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{amsbsy} \usepackage{mathrsfs} \usepackage{upgreek} \setlength{\oddsidemargin}{-69pt} \begin{document}$$-\Delta S(T)$$\end{document} curve across a very wide temperature span. The magnitude of entropy change has to be, however, improved by Ni–Ge tuning to enhance the relative cooling power. Regardless, a modest magnetocaloric effect with negligible hysteresis has been attained near room temperature via Ni-doping in MnCoGe alloy.