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.