The intrinsic exchange bias effect in the LaMnO₃ and LaFeO₃ compounds

This work investigates the magnetic and the intrinsic exchange bias (EB) properties of the sol-gel synthesised LaMnO₃ and LaFeO₃ perovskite compounds. The x-ray diffraction (XRD) has proved the high homogeneity of both compounds, which are crystallised in the orthorhombic Pnma structure (as proved by Rietveld refinement). The field cooling-zero field cooling magnetisation dependent temperature (M(T)) indicates the antiferromagnetic (AFM) nature of these compounds. Nevertheless, an anomalous ferromagnetic (FM) behaviour is observed, which is more likely, arises from the spin canting effect in the Mn³⁺ and Fe³⁺ ions. The thermal variation of the magnetisation reciprocal (M⁻¹) has confirmed the presence of this FM component below 110K in LaMnO³ and the Curie-Weiss behaviour above 160K. Also, the magnetic hysteresis loops below 110K are corresponding to the FM-like behaviour. The spin of the FM component couples with the AFM phase spins, leading to the EB effect in both compounds that show maximum values of −1124Oe and 2343 Oe for the LaMnO³ and LaFeO³ compounds, respectively. It is observed that the EB effect is suppressed with the partial substitution of La³⁺ by Ba²⁺ due to the dominance of the FM phase and the absence of the FM/AFM coupling. Also, the influence of the FM-AFM phases co-existence on the magnetocaloric(MCE) properties of the LaMnO₃ compound were studied. Where the LaMnO₃ compound shows a magnetic entropy change (ΔS) of 0.42 J/kg.K with an adiabatic temperature change (ΔT_ad) of 0.1k that is improved in the La_0·8Ba_0·2MnO₃ compound to 1.3 J/kg.K and 0.4K, respectively.