Superexchange antiferromagnetism and cryogenic magnetocaloric effect in scheelite-type GdTi0.5Mo0.5O4 compound

Abstract

Scheelite-type LnLiF4 compounds have become promising cryogenic magnetic refrigerants due to their giant low-field magnetocaloric effect (MCE). This work presents an example of a scheelite-type rare-earth transition metal oxide GdTi0.5Mo0.5O4. The magnetic interactions, magnetic phase transition (MPT) and MCE of GdTi0.5Mo0.5O4 compound were investigated through magnetization measurements and a mean-field approach. A mean-field model was used to elucidate the role of primarily superexchange antiferromagnetic (AFM) coupling on the magnetocaloric performance in this compound. From the analysis of the magnetization dependence, an isotropic AFM exchange coupling with energy scale εex = JnnS2 ≈ 1.7 K was estimated. The magnetic susceptibility reveals the occurrence of MPT from paramagnetic (PM) to AFM at the Néel temperature (TN ≈ 1.3 K). GdTi0.5Mo0.5O4 exhibits a large magnetic entropy change up to 43.3 J/(kg·K) at 1.3 K for μ0ΔH = 0−7 T, which makes it a cryogenic magnetic refrigerant with potential applications. Furthermore, a mean-field model with superexchange AFM above 3 K can well predict the MCE observed in GdTi0.5Mo0.5O4.