Charge ordering induced by Sr doping in 3% Cr-doped La0.45Ca0.55-xSrxMnO3

The relation between the average ionic radius of A-site cations (rA) and the Cr3+-Mn3+/4+ magnetic coupling has been investigated in 3% Cr-doped La0.45Ca0.55-xSrxMnO3. Cr-free La0.45Ca0.55MnO3 undergoes the transition from ferromagnetic (FM) to charge ordered antiferromagnetic (CO AFM) phases at low temperature. In the x = 0 and 0.1 compounds, Cr doping suppresses this transition, and FM metallic phases are observed even at low temperatures. Sr doping at x≥0.2 produces AFM components at low temperatures. Particularly, the CO AFM phase is observed at x = 0.25 and 0.3 despite Cr doping. Antiferromagnetic superexchange interaction between t2g (Cr) and t2g (Mn) through 2pπ (O) in Cr-O-Mn bonds is detectable only at x≥0.2. Strong AFM coupling between Cr3+ and its neighbouring Mn3+/4+ probably interferes with long-range FM ordering. There must be some correlation between Cr3+-Mn3+/4+ magnetic coupling and (rA), and the strong AFM t2g (Cr)-2pπ (O)-t2g (Mn) interaction is likely to enhance the charge ordering at x = 0.25 and 0.3