Magnetism study of spin correlations in Bi0.5Ca0.5MnO3

Magnetic properties of polycrystalline Bi0.5Ca0.5MnO3 are investigated by means of magnetization and electron spin resonance (ESR). The charge ordering (CO) and antiferromagnetic (AFM) transitions are determined from the temperature dependence of magnetization and ESR parameters. It is found that weak ferromagnetic (FM) spin correlations exist in the paramagnetic (PM) state. With temperature decrease, FM spin correlations are suppressed by gradually increased AFM spin correlations in the CO state and frozen in the long range AFM state at the AFM transition temperature T-N. Our study suggests that the competition between FM and AFM spin correlations is accompanied by a change of spin-orbit coupling and spin-lattice interaction.