Magnetostructural coupling, Kondo-like behavior, and magnetocaloric performance in Fe-doped Nd0.5(Sr0.4Ba0.1)CoO3 perovskites

Abstract

We comprehensively studied the structural, electronic, magnetic, electrical, and magnetocaloric properties of A- and B-site co-doped polycrystalline perovskites Nd_0.5(Sr_0.4Ba_0.1)Co_1−xFe_xO₃ (x = 0.0–0.2), which crystallize in a disordered orthorhombic phase with space group (62). Synchrotron X-ray diffraction (SXRD) analyses reveal stable valence states for Co and Fe ions across compositions, with progressive distortion of the [Co/Fe]O₆ octahedral symmetry as the Fe content increases. Magnetic measurements indicate a decrease in the paramagnetic–ferromagnetic transition temperature (T_C) from 211 K to 206 K, attributed to Fe^3+/4+ ↔ Co^2+/3+ random magnetic interactions. Temperature-dependent SXRD analysis shows anomalies in the volumetric coefficient of thermal expansion α_V(T) and U_iso mean square displacement, correlating with the T_C due to magnetoelastic coupling. The magnetocaloric effect (MCE) analysis reveals a second-order phase transition (SOFT) around T_C with a maximum magnetic entropy change −ΔS^max_M of 2.03 J kg⁻¹ K⁻¹ and a relative cooling power (RCP) of approximately 226 J kg⁻¹ for x = 0.12. The magnetic order exponents suggest long-range magnetic ordering. Furthermore, X-ray absorption near-edge structure spectroscopy (XANES) indicates consistent valence states for Co and Fe ions across all samples, with increased hybridization between Fe and O atoms due to Fe doping. The electrical resistivity analysis revealed metallic behavior with a notable upturn at ∼110 K, attributed to a localized-itinerant magnetism thermally driven, described by a Kondo–Bloch–Grüneisen type equation. These findings elucidate the role of Fe doping in modulating the structural, electronic, electric, and thermomagnetic properties of Nd_0.5(Sr_0.4Ba_0.1)Co_1−xFe_xO₃, offering valuable insights into the underlying magnetic phase diagram of this perovskite system.