Mechanism of enhanced magnetization in CoFe2O4/La0.7Sr0.3MnO3 composites with different mass ratios

Magnetization enhancement is observed in the bi-magnetic systems including paramagnetic (PM)/antiferromagnetic (AFM), AFM/AFM, and ferromagnetic (FM)/AFM composites systems, and attributed to the effects of oxidation states of metallic ions on the interface exchange-coupling. With respect to the FM/FM system, in this study, the enhanced magnetization in hard CoFe2O4 (CFO)/soft La0.7Sr0.3MnO3 (LSMO) composites with different mass ratios of LSMO (R-s) was observed for the first time. The values of saturation magnetization (M-s) of CFO and LSMO at 10 K were found to be 111 and 113 emu/g, respectively. For the CFO/LSMO composites, M-s was below 111 emu/g for R-s <= 15% because the antiferromagnetically coupled CFO/LSMO system maintains the super-spin glass (SSG) state with the moment of CFO particles being randomly oriented. However, M-s increases to 133 and 127 emu/g for R-s = 18 and 21%, respectively, because the higher content of LSMO separates the CFO particles and destroys the SSG state, thus enabling the moment of CFO particles to rotate easily and align with the external magnetic field. Mechanism for the magnetization enhancement reported herein is different from the interface exchange-coupling mechanism, which enriches the understanding of the magnetization reversal in bi-magnetic systems and provides the experimental reference for the applications of bi-magnetic materials.