Enhanced exchange bias effect in size modulated Sm_0.5Ca_0.5MnO₃ phase separated manganite

Abstract

The effect of grain size modulation on exchange bias effect in CE-type antiferromagnetic Sm_0.5Ca_0.5MnO₃ phase separated manganite is reported here. With the reduction of particle size, ferromagnetic clusters are found to form in the charge ordered antiferromagnetic matrix and gradually become larger. The horizontal and vertical shifts of the magnetic hysteresis loops in the field cooled magnetization process clearly indicate the size dependent exchange bias effect and it can be tuned with the reduction of particle sizes. The values of exchange bias parameter, i.e., exchange bias field (H_E), coercivity (H_C), remanence asymmetry (M_E), and magnetic coercivity (M_C) are found to depend strongly on the particle size. The variations of H_E follow non-monotonic dependencies with reduction in particle size and show maximum (1205 Oe) at particle size of 150 nm at T = 5 K, which can be ascribed due to the changes in uncompensated surface spins. The values of H_E and M_E are found to decrease exponentially with increasing temperature below the spin- or cluster-glass like freezing temperature. The spin relaxation model has been employed for analysis of large magnetic training effect. The linear relationship between H_E and M_E further confirms the role of uncompensated surface spins. In view of spintronics application of manganites, the present observation of large exchange bias shift in this half-doped manganite may have great technological importance.