2017 年 64 巻 7 号 p. 347-354
Exchange-coupled nanocomposite magnets (NCMs) consisting of hard and soft magnetic phases have attracted much attention as novel permanent magnets. We previously succeeded in fabrication of L10-FePd/α-Fe NCMs by the reductive annealing of Pd/γ-Fe2O3 heterostructured nanoparticles. Herein we explain the structural optimization of L10-FePd/α-Fe NCMs by adjusting the volume fraction of hard/soft phases and the temperature of reductive annealing to obtain large maximum energy products ((BH)max). The sample with a hard/soft volume ratio of 82/18 formed by annealing at 773 K had the largest (BH)max = 10.3 MGOe. In these L10-FePd/α-Fe NCMs with the large (BH)max, the interface between the hard and soft phases was coherent and the phase sizes were optimized, both of which effectively induced exchange coupling. This exchange coupling was directly observed by visualizing the magnetic interaction between the hard and soft phases using a first-order reversal curve (FORC) diagram.
