Ferromagnetic insulating and reentrant spin glass behavior in Mg doped La0.75Sr0.25MnO3 manganites

In this study, the effect of Mg substitution on structural, magnetic and electrical properties of La0.75Sr0.25Mn1−xMgxO3 and La0.75Sr0.25−xMgxMnO3 (nominal compositions) samples are investigated by XRD, Ac susceptibility and electrical resistivity measurements. It is found that Mg does not replace La in the perovskite lattice. Also the results show that by increasing Mg doping levels, the paramagnetic–ferromagnetic and metal–insulator transition temperatures decrease. The reason for decreasing transition temperatures with increasing Mg concentration is, that the long-range FM order has been destroyed by the Mg, which is randomly occupying Mn site. This leads to the suppression of double-exchange interaction in the Mn3+–O–Mn4+ networks. Also the reentrant spin glass (RSG) state accompanied by FM transition, exists in high doped samples. The RSG state could be understood on the basis of double exchange ferromagnetic interaction in Mn3+–O–Mn4+ and super-exchange antiferromagnetic interaction in the Mn4+–O–Mn4+ networks.