ELUCIDATING SIZE EFFECTS ON THE COMPETING MAGNETIC PHASES IN La1-x-yPryCaxMnO3 IN BULK POLYCRYSTALS

Abstract

Mixed valence manganese oxides R1−xAxMnO3 (R = rare earth cation such as La, Pr, Nd, Sm, etc., and A = divalent cation, such as Ca, Sr, Ba, etc.) have been famous for long time. These complex metal oxides have been studied as far back as 1950 for their interesting structural, magnetic, and electronic behaviour, especially a certain class of manganese oxide, the manganite perovskites. The perovskite manganites are well established and widely investigated materials belonging to the strongly correlated family because of the intimate and intricate coupling between the different degrees of freedom. The major degrees of freedom in these type of materials are associated with the lattice, charge, orbital and spin and the interplay between them leads to a wide variety of structural, electronic, and magneto-electric phases like paramagnetism (PM), charge ordering (CO), ferromagnetism (FM), antiferromagnetism (AFM), spin glass behaviour, metal-insulator transition (IMT), and colossal magnetoresistance (CMR) etc. In manganites, one of the most widely studied phenomena has been the phase transition from the antiferromagnetic charge ordering (AFM-CO) to a charge disordered ferromagnetic metallic (CD-FMM) state. The charge ordering is synchronous to the AFM spin order having an insulating flavour, while the charge disordered state comes with FM spin order and metallic flavour. Thus, the AFM-super-exchange (SE) competes with the FM-DE interaction. This type of competition between AFM and FMM phases gives rise to a variety of interesting dimensions to the phase competition as manifested in the magnetic and magnetotransport properties. Such phase competition scenario is termed as the phase separation (PS). The competing FM and AFM phases in manganites incite magnetic frustration and when frozen it causes the existence of glassy behaviour. Several studies have reported the findings on the glassy behaviour in manganites, which is attributed to the interaction between the phase separated clusters and not to the competition between DE and SE interactions.