Unveiling the structural and magnetic properties of RENaGeO4 (RE = Gd, Dy, and Ho) oxides and remarkable low-temperature magnetocaloric responses in GdNaGeO4 oxide

Abstract

The low-temperature magnetocaloric (MC) responses in various type solid-state magnets have been extensively determined, aimed for developing high-performing MC materials for magnetic refrigeration application and deepen our understanding of their underlying intrinsic magneto-physical characters. We herein fabricated a family of single-phased rare-earth (RE)-dominated, namely the RENaGeO4 (RE = Gd, Dy, and Ho) oxides, by solid phase reaction method and unveiled their structural and magnetic properties, specifically to low-temperature MC responses by experimental determination and theoretical calculation. All of these RENaGeO4 oxides crystallize in an orthorhombic Olivine-type structure with the space group of Pnma (No. 62) and order magnetically at the temperatures of 0.70, 2.28, and 2.15 K for GdNaGeO4, DyNaGeO4, and HoNaGeO4 oxides, respectively. The consistent elements in these RENaGeO4 oxides are all distributed uniformly and present as RE3+, Na1+, Ge4+, and O2- valence states, respectively. The low-temperature MC responses in these RENaGeO4 oxides are identified by the MC parameters of maximum magnetic entropy change and relative cooling power. These MC parameters under magnetic field changes (H) of 0-2/0-5 T as follows: 34.98/47.30 J/(kg·K) and 107.56/320.70 J/kg for GdNaGeO4, 11.23/14.82 J/(kg·K) and 77.70/236.82 J/kg for DyNaGeO4, and 12.21/15.37 J/(kg·K) and 81.18/239.47 J/kg for HoNaGeO4, respectively. Evidently, these determined MC parameters for GdNaGeO4 oxide, especially under relatively low H, are much larger than those of the commercial MC material of Gd3Ga5O12 oxide and surpass most updated benchmarked low-temperature MC materials, making the GdNaGeO4 oxide as an excellent candidate for low-temperature magnetic refrigeration application.