Fabrication of exchange-coupled α-Fe∕L1-FePd nanocomposite isolated particles

Abstract

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 L1 0-FePd/α-Fe NCMs by the reductive annealing of Pd/γ-Fe 2 O 3 heterostructured nanoparticles. Herein we explain the structural optimization of L1 0-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 L1 0-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. KEY WORDS nanocomposite magnet, L1 0-FePd/α-Fe, heterostructured nanoparticle, maximum energy product, first-order reversal curve diagram @@@@@@@@@@@@@@@@@ 53% 1% 1 1)

Exchange Coupling Interaction in L10-FePd/α-Fe Nanocomposite Magnets with Large Maximum Energy Products

“…Additionally, because of the extreme phase-segregation, the soft phase size increased relative to the evaluated exchange length, which is approximately 10 nm in the case of Fe as a soft phase. 23 EDX line analysis of the annealed sample indicated that the L1 0 -FePd and R-Fe phases had nanometer size distributions and that the L1 0 -FePd and R-Fe phases were neighboring each other (Supporting Information, Figure S5). Consequently, it was clarified that the soft phase was in coherent contact with the hard phase within an exchange interaction length.…”

“…At higher annealing temperatures, both phases became coarser rapidly, leading to noncoherent contact at the interface (Figure g−l). Additionally, because of the extreme phase-segregation, the soft phase size increased relative to the evaluated exchange length, which is approximately 10 nm in the case of Fe as a soft phase . EDX line analysis of the annealed sample indicated that the L 1 0 -FePd and α-Fe phases had nanometer size distributions and that the L 1 0 -FePd and α-Fe phases were neighboring each other (Supporting Information, Figure S5).…”

One-Pot Synthesis of Urchin-like FePd–Fe3O4 and Their Conversion into Exchange-Coupled L10–FePd–Fe Nanocomposite Magnets

“…On cooling from the eutectoid temperature to room temperature, α-Fe and L10−FePd can be obtained. 30 This simultaneous formation of L10−FePd and α-Fe as a thermodynamically stable mixture indicates that L10−FePd−Fe is a better model system to study nanocomposite magnets with controlled exchange-coupling.…”

Exchange‐Coupled fct‐FePd/α‐Fe Nanocomposite Magnets Converted from Pd/Fe3O4 Core/Shell Nanoparticles

“…To date, limited attempts have been made to prepare fct-FePd/Fe nanocomposites. [24,[27][28][29] Yu et al reported the synthesis of fct-FePd/Fe nanocomposites annealed from urchin-like FePd-Fe 3 O 4 composites. [27] By promoting the interfacial diffusion between Pd and Fe, fct-FePd/Fe nanocomposites could also be obtained from the mixture of Pd/Fe 2 O 3 and Pd NPs, in which extra Pd NPs were used to control the volume fraction of hard/soft magnetic phases in the nanocomposites.…”