Magnetic transitions with magnetocaloric effects near room temperature related to structural transitions in Y0.9Pr0.1Fe2D3.5 deuteride

The structural and magnetic properties of Y0.9Pr0.1Fe2D3.5 deuteride have been investigated by synchrotron and neutron diffraction, magnetic measurements, and differential scanning calorimetry. Deuterium insertion induces a 23.5% cell volume increase and a lowering of crystal symmetry compared to the cubic C15 Y0.9Pr0.1Fe2 parent compound (Fd-3m SG). The deuteride is monoclinic (P21/c SG) below 330 K and undergoes a first-order transition between 330 and 350 K toward a pseudo-cubic structure (R-3 m SG) with TO–D = 342(2) K. In both structures, the D atoms are located in 96% R2Fe2 and 4% RFe3 tetrahedral interstitial sites (R = Y0.9Pr0.1). The compound is ferromagnetic, accompanied by a magnetostrictive effect below TC = 274 K. The analysis of the critical exponents indicates a second-order type transition with a deviation from the isotropic 3D Heisenberg model toward the 3D XY model. This implies an easy plane of magnetization in agreement with cell parameter variation showing planar magnetic orientation. A weak magnetic peak is even observed at the order–disorder transition with a maximum at 343 K. Magnetic entropy variations are characteristic of direct and inverse magnetocaloric effects at TC and TO–D, respectively.