A comparative magnetic behaviour of conventional and high entropy double perovskites: La2MnCoO6 and (La0.4Y0.4Ca0.4Sr0.4Ba0.4)MnCoO6

Abstract Here we report the synthesis, structure and magnetic properties of La2MnCoO6 and the high entropy stabilized (La0.4Y0.4Ca0.4Sr0.4Ba0.4)MnCoO6. The samples were characterized using powder X-ray diffraction (PXRD), transmission electron microscopy (TEM), electron diffraction (ED), energy-dispersive X-ray spectroscopy (EDX) elemental mapping analysis together with high-angle annular dark field scanning transmission electron microscopy (HAADF-STEM) and magnetization studies. PXRD and ED studies confirm the orthorhombic and cubic symmetry of La2MnCoO6 and (La0.4Y0.4Ca0.4Sr0.4Ba0.4)MnCoO6, respectively. The elemental mapping confirms the chemical homogeneity of the samples. The high temperature magnetic ordering at TC ~ 225 K expected for an atomically ordered La2MnCoO6 is suppressed in the corresponding quenched sample. The atomic disordering in quenched La2MnCoO6 results in coexistence of the phases where vibronic ferromagnetism and antiferromagnetic states appeared at TC ~ 135 K and TN ~ 150 K, respectively. Whereas the high entropy stabilized (La0.4Y0.4Ca0.4Sr0.4Ba0.4)MnCoO6 exhibits antiferromagnetic transition at TN ~ 150 K and low temperature magnetic frustration at 45 K and 15 K due to localized competing interactions. The drastic suppression of ferromagnetic state in (La0.4Y0.4Ca0.4Sr0.4Ba0.4)MnCoO6 suggests that the essential interaction is of antiferromagnetic nature in cationically disordered La2MnCoO6 perovskite. We have suggested that the size disorder parameter, σ 2 = ∑ i x i r i 2 - r A > 2 plays a significant role in determining the magnetic ground state of the high entropy stabilized perovskite.