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

At 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 mu(B) 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 T-C 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 (Delta S-M) are measured near T-C for the M1 and C2 phases, near TFM-AFM for the M2 phase, whereas positive Delta S-M peaks due to inverse MCE effect are found near TO-D. A structural and magnetic phase diagram is proposed. (c) 2022 Elsevier B.V. All rights reserved.

Automated summary

At different temperatures, the structures and magnetic properties of Y0.9Gd0.1Fe2Hx hydrides change sequentially. Above 300K, they undergo a first-order transition and exhibit negative and positive magnetic entropy variations. The proposed structural and magnetic phase diagram provides a better understanding of the properties of these hydrides.