Role of anti-site disordering in magnetic properties of Sm2NiMnO6 double perovskite

We have investigated the structural, magnetic and electronic properties of B-site disordered Sm₂NiMnO₆ DP oxide. XPS measurements indicate mixed valency of both Ni²⁺/³⁺ and Mn⁴⁺/³⁺ species. RE₂NiMnO₆ ordered DP is commonly believed to show two magnetic phase transitions viz, PM-FM transition at T_C due to Ni^2+/3+-O-Mn^4+/3+ super exchange interaction and at T_f due to coupling of RE spins with Ni-Mn network [1, 2]. In our present study, we have observe that the presence of intrinsic B-site disorder results in an additional AFM coupling [3], mediated by Ni^2+/3+-O-Ni^2+/3+ and Mn^4+/3+-O-Mn^4+/3+ pairs. In M(T) measurements we have observed an inverted cusp like trend and thermal irreversibility in FCC and FCW cycles in T_f<T<T_C both of which vanishes on application of higher magnetic fields. The observed thermal hysteresis indicates towards the possibility of either coexisting FM-AFM phases or magnetic frustration originating from different exchange interaction paths between mixed valence ions. MH isotherms in T_f <T<T_C exhibit two step reversibility loop behavior, which further confirms the presence of competing FM-AFM phases.
[1]. Lekshmi, et al, J. Mater. Chem. C, 2013, 1, 6565.
[2]. Yang, et al, J. Appl. Phys., 2012, 112, 064104.
[3]. D. Sanchez, et al., Phys Rev. B, 2002, 65, 104426.