The order of magnetic phase transitions in disordered double perovskite oxides Sm2FeCoO6 and Dy2FeCoO6

We present the results on the order of phase transition around the spin re-orientation region using isothermal magnetization data performed on the sol-gel synthesized disordered double perovskite oxides Sm2FeCoO6 and Dy2FeCoO6 by Arrott plot method. The temperature variation of the DC magnetization data of both the samples show that there are two magnetic phase transitions; one at high temperature regime, the conventional paramagnetic (PM) to ferro or ferrimagnetic (FM or FIM) and the other at low temperatures, ferro or ferrimagnetic (FM or FIM) to antiferromagnetic (AFM). From the Arrott plot method, it is inferred that spin re-orientation transitions of both the compounds has a first order nature corresponding to the FM (FIM) to AFM transition.