Magnetocaloric behavior and magnetic ordering in MnPdGa

Abstract

MnPdGa, a compound crystallizing in the ${\\mathrm{Ni}}_{2}\\mathrm{In}$ structure, is a material displaying magnetic ordering near room temperature and is a potential ambient-temperature magnetocaloric. Screening based on electronic structure calculations suggest that MnPdGa may exhibit a high magnetocaloric figure of merit due to its strong magnetostructural coupling. Here we report the preparation of MnPdGa and employ high--resolution synchrotron x-ray diffraction to confirm its hexagonal ${\\mathrm{Ni}}_{2}\\mathrm{In}$-type structure. The zero-field ground state is shown to be a conical spin-wave state, defined by a long-range modulation of the conventional conical antiferromagnet structure. Near the Curie temperature, the measurements carried out here coupled with electronic structure calculations suggest that a fully ferromagnetic state can form at elevated temperatures under an applied field. A peak magnetocaloric entropy change $\\mathrm{\\ensuremath{\\Delta}}{S}_{M}=\\ensuremath{-}3.54\\phantom{\\rule{0.28em}{0ex}}\\mathrm{J}\\phantom{\\rule{0.28em}{0ex}}{\\mathrm{kg}}^{\\ensuremath{-}1}\\phantom{\\rule{4pt}{0ex}}{\\mathrm{K}}^{\\ensuremath{-}1}$ ($30.1\\phantom{\\rule{0.16em}{0ex}}\\mathrm{mJ}\\phantom{\\rule{0.16em}{0ex}}{\\mathrm{cm}}^{\\ensuremath{-}3}\\phantom{\\rule{0.16em}{0ex}}{\\mathrm{K}}^{\\ensuremath{-}1}$) is measured at ${T}_{C}\\phantom{\\rule{0.16em}{0ex}}=\\phantom{\\rule{0.16em}{0ex}}315\\phantom{\\rule{0.16em}{0ex}}\\mathrm{K}$ at an applied field $H=5\\phantom{\\rule{0.16em}{0ex}}\\mathrm{T}$. The exchange-driven, nontrivial magnetic structure found in MnPdGa is compared with the somewhat better-studied MnPtGa on the basis of electronic structure calculations.