Simultaneous enhancements of magnetization and remanence in sufficiently exchange-coupled Co0.8Al0.2Nd Fe2−O4/Co7Fe3(Co) composites

Abstract Hard/soft magnetic Co0.8Al0.2NdxFe2−xO4/Co7Fe3(Co) composites are synthesized by the ball-milling-assisted ceramic process, followed by 5% H2-Ar reduction. The effects of the reduction time on their structure and magnetic properties are studied at room temperature. XRD patterns indicate that Co0.8Al0.2NdxFe2−xO4 sample, calcined at 900 °C for 3 h, contains the main spinel CoFe2O4 phase in combination of a small amount of foreign Fe2O3 and/or FeNdO3 phases. After being reduced at 550 °C for 30 min, surface magnetic particles of spinel Co0.8Al0.2NdxFe2−xO4 ferrite samples are transformed from the hard magnetic Co0.8Al0.2NdxFe2−xO4 to the soft magnetic Co7Fe3(Co). The magnetic measurement suggests that the specific saturation magnetization and remanence of spinel Co0.8Al0.2NdxFe2−xO4 decrease with increasing Nd3+ content. After being reduced at 550 °C, specific saturation magnetization and remanence of the composites, Co0.8Al0.2NdxFe2−xO4/Co7Fe3(Co), increase markedly. The hysteresis loop of the composites shows a single-phase magnetization behavior, implying that the magnetic hard (Co0.8Al0.2NdxFe2−xO4) phase and soft [Co7Fe3(Co) alloy] phase in Co0.8Al0.2NdxFe2−xO4/Co7Fe3(Co) composites are well exchange-coupled, which is confirmed by the switching field distribution curves further.