The effect of Ca-substitution in La-site on the magnetic properties of La2CoMnO6.

Double perovskite La_2-xCa_xCoMnO₆ (x=0, 0.1, 0.2, 0.5) ceramics samples were synthesized by the standard solid-state reaction method. The crystal structures have been confirmed to be monoclinic perovskite structure with space group of P21/n at room temperature by the powder x-ray diffraction (Cu-Ka). The grains of the samples are relatively dense and distribute in random directions from the scanning electron microscope patterns. Holes are doped into La₂CoMnO₆ with the substitution of the Ca²⁺ ions in La-site, and further lead to the valences of Mn ions and Co ions transforming from Mn⁴⁺ and Co²⁺ to Mn³⁺ and Co³⁺, respectively. Ferromagnetic coupling of Mn⁴⁺-O^2--Co²⁺ and antiferromagnetic coupling of Mn₃₊-O^2--Co³⁺ are coexistent in La_2-xCa_xCoMnO₆ system, which correspond to two transitions existed in field-cooling magnetization versus temperature curves. Curie temperature of La_2-xCa_xCoMnO₆ system decreases with the increasing of Ca-substitution amount. The coexistence of different magnetic phases leads to the exchange bias effect. [ABSTRACT FROM AUTHOR]