Magnetic, structural and magnetocaloric properties of Y0.9Gd0.1Fe2Hx hydrides

International audienceAt 300 K, Y0.9Gd0.1Fe2Hx hydrides crystallize sequentially with increasing H concentration in various structures related to a lowering of the cubic MgCu2 type structure of the parent alloy: cubic C1, monoclinic M1, cubic C2, monoclinic M2, cubic C3, orthorhombic O. Above 300 K, they undergo a first-order transition at a TO-D temperature driven by order-disorder of hydrogen atoms into interstitial sites. Their magnetic, structural and magnetocaloric properties have been investigated through magnetic measurements, and high-resolution synchrotron diffraction experiments. The magnetization at 5 K decreases slightly from 4 to 3.8 μB for x = 3–3.9 H/f.u., then with a larger slope for higher H content. A discontinuous decrease of the magnetic transition temperature is observed: M1 and C2 hydrides are ferrimagnetic with TC near 300 K, M2 hydride displays a sharp ferromagnetic-antiferromagnetic transition at TFM-AFM = 144 K, whereas C3 and O hydrides present only a sharp increase of the magnetization below 15 K and a weak magnetization up to room temperature. Negative magnetic entropy variations (ΔSM) are measured near TC for the M1 and C2 phases, near TFM-AFM for the M2 phase, whereas positive ΔSM peaks due to inverse MCE effect are found near TO-D. A structural and magnetic phase diagram is proposed