Influence of Cation Order and Valence States on Magnetic Ordering in La₂Ni_1−xMn_1+xO₆

Among multifunctional double perovskite oxides, La₂NiMnO₆ has recently drawn significant attention due to its importance both in terms of understanding of fundamental physics and potential for device applications. The relative alteration in Ni:Mn ratio strongly influences the structural and magnetic properties of La₂NiMnO₆. The cation ratio and degree of cation order significantly affect the magnetic coupling of the two B-site cations in these compounds. In the present study, La₂Ni_1−xMn_1+xO₆ (x = −0.25, 0, 0.25) samples with different Ni:Mn ratio have been prepared using sol–gel method and modifications of the above physical properties from that of a stoichiometric sample of La₂NiMnO₆ are discussed. The crystalline structures of the samples varied with different ionic ratios. While all samples exhibited ferromagnetic behavior, long-range Ni/Mn magnetic ordering was detected in selected samples only. The experimental values of saturation magnetization were smaller than the theoretical spin-only moments, which suggests a less ordered state for all samples. Due to an increased antiferromagnetic interaction caused by antisite disorders, the saturation magnetization decreases while the coercive field increases with decreasing Mn content.