Growth of ordered and disordered epitaxial thin films of Lu2MnNiO_6 using (001)-LaAlO_3 and (001)-SrTiO_3 substrates: Observation of six monoclinic in-plane twin variants and glassy magnetic behaviour

摘要

It is well known that in double perovskites, the degree of cation ordering plays a very important role in determining the intrinsic magnetic properties. Therefore, in order to distinguish between the intrinsic properties and the disordered cation driven magnetic properties, we have grown ordered and disordered epitaxial thin films of Lu2MnNiO_6 (LMNO) using two different cubic substrates (001)-LaAlO_3 and (001)-SrTiO_3 (LAO and STO respectively) by pulsed laser deposition (PLD) method. It is found that both LMNO films grow in monoclinic crystal symmetry and possess two out-of-plane domains (110) and (001). Moreover, various in-plane rotations of these domains give rise to a total of six in-plane twin variants. The films show dominant ferromagnetic nature. Due to good lattice matching with LAO, LMNO/LAO films are well-ordered and exhibit a sharp ferromagnetic to paramagnetic transition at 7c = 38 K, whereas, the large lattice mismatch with STO resulted in disordered LMNO/STO films and T_C is lowered to 34 K. The value of maximum magnetization (Ms, at 70 kOe) in disordered LMNO/STO (M_S = 2.4_(μB)/f.u.) is almost half of that in the ordered LMNO/LAO (M_S = 4.0_(μB)/f.u.). Interestingly, the well-ordered LMNO/LAO films show memory effect and relaxation of magnetization in the entire temperature range below TC. This is in conformance to the intrinsic glassy magnetic nature of LMNO.