(ESICMM-G8 Symposium on Next Generation Permanent Magnets, Tsukuba, 2015)
Improvement in Magnetic Properties of L10-FePd/α-Fe Nanocomposite Magnets with Precisely Controlled Nanostructures


R. Sato, T. T. Trinh, K. Matsumoto, and T. Teranishi (Kyoto University)
N. Sakuma (Toyota Motor Corporation)

Abstract:

1. Introduction
  Exchange-coupled nanocomposite magnets (NCMs) consisting of nanosized hard and soft magnetic phases have attracted much attention as high-performance permanent magnets due to their large theoretical maximum energy products ((BH)max), compared with conventional single-phase magnets. We previously succeeded in fabrication of exchangecoupled L10-FePd/α-Fe NCMs via reduction and subsequent interfacial atom diffusion of anisotropically phase-segregated Pd/γ-Fe2O3 nanoparticles (NPs) synthesized by chemical liquid phase reaction.[1] To achieve further enhancement of the magnetic performance of L10-FePd/α-Fe NCMs, we investigated suitable nanostructures in detail so as to induce the effective exchange coupling between L10-FePd and α-Fe phases.
2. Structural Optimization
  Structurally optimized L10-FePd/α-Fe NCMs with large (BH)max (10.3 MGOe) were prepared by adjusting the volume fraction and grain size of hard and soft phases. In L10-FePd/α-Fe NCMs with relatively-large (BH)max, the coherent interface between the (111) plane of L10-FePd and the (110) plane of α-Fe was confirmed 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.[2]
Figure. TEM images of as-synthesized samples. (a) 15 nm cubic and
(b) 18 nm octahedral Pd NPs were used as cores of (c) cubic and (d)
octahedral Pd@FeOx NPs. Reductive annealing of (c) and (d) provided
L10-FePd/α-Fe isolated NPs in (e) and (f), respectively.
3. Interfacial Control
  To form the foregoing coherent interface efficiently, interfacial controls in L10-FePd/α-Fe NCMs were performed by the precise shape control of Pd NPs. L10-FePd/α-Fe isolated NPs were chemically synthesized and reductively annealed from {100}-enclosed Pd nanocubes and {111}-enclosed Pd nanooctahedra, and their corresponding Pd/FeOxcore/shell (Pd@FeOx) NPs, respecttively (see Figure). The research addressed to the aspects of interest from controlling primary (size, shape, composition, and interface) to secondary (regular ordering) structures of exchange- coupled L10-FePd/α-Fe NCMs. As expected, the resulting NPs, particularly octahedral shape, showed a significant magnetic improvement.[3]
Acknowledgement
  These works were partially supported by MagHEM (NEDO).
References
[1] Teranishi, T.; Sakuma, N. et al. J. Am. Chem. Soc. 2008, 130, 4210–4211.
[2] Sakuma, N.; Sato, R.; Teranishi, T. et al. ACS Nano 2011, 5, 2806–2814.
[3] Trinh, T. T.; Sato, R.; Matsumoto, K.; Sakuma, N.; Ito, N.; Teranishi, T., manuscript in preparation.