Magnetoelastic coupling and cryogenic magnetocaloric effect in two-site disordered GdSrCoFeO6 double perovskite

Abstract

The development of new magnetic refrigerants demands an effective investigation of materials with a large magnetocaloric effect in a wide temperature range. Herein, we report on the structural, magnetic, and magnetocaloric properties of the two-site disordered double perovskite GdSrCoFeO6 prepared by the modified solid-state synthesis method. Temperature-dependent synchrotron X-ray diffraction analysis revealed that GdSrCoFeO6 crystallizes in the orthorhombic phase (Pnma), with Gd3+/Sr2+ and Co2+/3+/Fe3+/4+ ions randomly distributed on the A- and B-sites, respectively. An observed lattice parameter anomaly around 60 K indicates the occurrence of the magnetoelastic coupling, which coincides with the presence of ferro/ferrimagnetic (FM/FiM) ordering below TC ≈ 65 K from the magnetic measurements. These results match well with our first-principles calculation prediction of low-temperature magnetic (FM/FiM) and electronic (insulating/metal) transitions related to a combined effect of Co and Fe short- and long-range competitions, crossings of spin state at Co ions, and the hybridization degree between Gd-4f and Co-3d states. Additionally, a modified Arrott plot and Kouvel–Fisher analysis were used to establish the nature of the magnetic phase transition in GdSrCoFeO6, yielding the critical exponent β = 1.46(6)/1.45(6), γ = 1.48(5)/1.17(2), and δ = 2.01(3)/1.80(5), respectively. The specific heat analysis reveals two well-defined broad peaks (∼10 and ∼70 K), which match well with a Schottky anomaly (Gd-4f) and the magnetic transition of FM/FiM to paramagnetic order, respectively. The magnetocaloric effect (MCE) analysis reveals a maximum magnetic entropy change ΔSMmax ≈ 13 J kg–1 K–1 (at ∼8 K) under a field of 0–7 T. These results evidence that the Schottky anomaly and the magnetoelastic coupling seem to be key factors for driving further enhancements to the MCE in GdSrCoFeO6, making it a possible candidate for cryogenic applications.