Synthesis, structure and magnetic properties of La1-x Ln xCr0.5Co0.5O3 (x = 0 and 0.2 & Ln = Pr, Sm and Gd) perovskites

We report the sol–gel synthesis of La_1-xLn_xCr_0.5Co_0.5O₃ (x = 0 and 0.2 & Ln = Pr, Sm and Gd) perovskites. The samples were characterized using powder X-ray diffraction (PXRD), field emission scanning electron microscopy (FE-SEM), energy dispersive X-ray (EDX) and magnetization measurements. It is worth mentioning that all the samples in this study are found to be monophasic as attested from the PXRD patterns in sharp comparison with the previously reported work on LaCr_0.5Co_0.5O₃ [Solanki et al. J. Magn. Magn. Mater. 469 (2019) 95–99.]. This could be related to the slight modifications in synthesis condition like the metal to citric acid ratio, drying as well decomposition temperature of gel, final calcination temperature and time. The parent phase (x = 0) crystallizes in rhombohedral, R-3c, structure whereas the Ln-doped samples are orthorhombic, Pbnm. FE-SEM imaging revealed the irregular shape and large variation in particle size. The particles are highly agglomerated but show faceted surface irrespective of shape and size. The EDX analysis confirms the nominal cationic composition of the samples. The magnetic measurements suggest the onset of antiferromagnetic ordering in all the samples with T_N ranging from 130 K to 124 K depending on the size of the Ln-dopant ion. The high temperature effective paramagnetic moments obtained from Curie-Weiss law for all the samples suggest that the most likely spin-state of cobalt is intermediate-spin state. The low temperature magnetic behaviour of the substituted samples could be related to the rare earth-transition metal interaction. The magnetic ground states can be attributed to the Cr³⁺–O–Co³⁺, Cr³⁺–O–Cr³⁺ and Co³⁺–O–Co³⁺ antiferromagnetic superexchange interactions between the randomly distributed Cr³⁺ and Co³⁺ ions.