Structural and Magnetic Properties of <i>B</i>-Site-Ordered <i>RE</i>₂CuTiO₆ (<i>RE</i> = Dy, Ho, and Er) Double-Perovskite Oxides with Significant Cryogenic Magnetocaloric Performance

Abstract

The magnetocaloric effect (MCE) is currently intensively investigated in various rare earths (<i>RE</i>)-containing magnetic solids, not only for developing appropriate magnetocaloric materials (MCMs) for cryogenic magnetic cooling but also for deepening our understanding into the inherent physical properties of these materials. Here, we provide a systematic experimental investigation into a series of new <i>RE</i>₂CuTiO₆ (<i>RE</i> = Dy, Ho, Er) double-perovskite (DP) oxides regarding the structural and magnetic properties, especially for their cryogenic MCE and magnetic-phase transition (MPT). All of these <i>RE</i>₂CuTiO₆ oxides crystallize in a <i>B</i>-site-ordered hexagonal DP-type structure with the symmetry of the crystallographic space group <i>P</i>6̅<i>m</i>2. These DP oxides exhibit magnetic ordering, with MPT temperatures of approximately 2.7, 2.2, and 2.7 K for Dy₂CuTiO₆, Ho₂CuTiO₆, and Er₂CuTiO₆, respectively. The magnetocaloric performances of the <i>RE</i>₂CuTiO₆ DP oxides were characterized by the peak values of magnetic entropy change, the temperature-averaged magnetic entropy change (5K-lift), and relative cooling powers. These magnetocaloric parameters were deduced to be 18.7/17.9 J/kgK and 298.2 J/kg for Dy₂CuTiO₆, 12.5/12.2 J/kgK and 273.9 J/kg for Ho₂CuTiO₆, and 13.8/12.9 J/kgK and 188.4 J/kg for Er₂CuTiO₆ under a magnetic field change of 0-5 T. These values are comparable to those of most reported <i>RE</i>-containing magnetocaloric materials, indicating that these <i>RE</i>₂CuTiO₆ DP oxides are promising candidates for cryogenic magnetic cooling applications.