Unusual dynamic magnetic behavior of polycrystalline La2NiMnO6

Single-phase polycrystalline La2NiMnO6 was studied by means of magnetization and specific heat measurements. This monoclinic perovskite material shows ferromagnetic behavior with Tc about 270 K. ac Susceptibility of the sample shows a strong frequency dependent behavior. Fitting results of the relationship between freezing temperature and frequency indicate that the present sample can be better described as a system with superparamagnetic (SPM) behavior. This dynamic magnetic behavior was further confirmed by the weak magnetic relaxation and memory effect. The SPM behavior was explained in terms of formation of clusters in the magnetic background. Moreover, specific heat at 0 T and 9 T both shows broad transition around Tc.