Teranishi Lab.
High-Performance Magnetic Devices using Ferromagnetic Nanoparticles
The as-synthesized particles generally have a chemically-disordered fcc structure, while annealing above 600C under either a vacuum, inert gas, or reducing atmosphere, transforms the crystal structure from fcc to the chemically-ordered L10 phase. The obtained L10-FePt nanoparticles are expected to be applied to permanent magnetic devices, such as ultra high-density recording media, and the hard magnetic phase of nanocomposite magnets, owing to high uniaxial magnetocrystalline anisotropy and high coercivity. On the other hand, nanocomposite magnets have attracted a great deal of interest for large energy permanent magnets due to the magnetic exchange coupling between the soft magnetic phase with a high saturation magnetization and the hard magnetic phase with a large uniaxial magnetocrystalline anisotoropy. For this purpose, both the hard and soft phases should be controlled at the nanometer scale. The chemically ordered L10-FePd nanoparticles have a great potential for application to the hard magnetic phase of nanocomposite magnets because the L10 phase is stably formed even from the Fe-rich FePd alloy at high temperature.
Size Control and Magnetic Properties of FePt Nanoparticles
(upper) AB and ABC stacking structures of 3.1 nm FePt nanoparticles,
(lower) Dependence of coercivity on the composition of FePt nanoparticles annealed at 600C.
[Ref.] Chem. Lett. 2004, 33, 130.; Trans. Mater. Res. Soc. Jpn. 2005, 30, 579.
TEM images of (a) 6.1±0.6 nm Fe36Pt64, (b) 5.8±0.7 nm Fe44Pt56, and (c) 5.1±0.7 nm Fe49Pt51 nanoparticles.
It was found that the crystal structure of these large FePt nanoparticles could be converted from fcc to L10
by annealing at 700C without significant coalescence.
[Ref.] Langmuir 2006, 22, 3485.
[Collaborator] Prof. Hiroshi Kitagawa at Kyushu University
Magnetization curves of 5.1±0.7 nm Fe49Pt51 nanoparticles annealed under Ar+4%H2 at 300C for 1, 3, and 5 h.
[Ref.] J. Phys. Chem. C 2007, 111, 7231.
(upper) AB and ABC stacking structures of 3.1 nm FePt nanoparticles,
(lower) Dependence of coercivity on the composition of FePt nanoparticles annealed at 600C.
[Ref.] Chem. Lett. 2004, 33, 130.; Trans. Mater. Res. Soc. Jpn. 2005, 30, 579.
TEM images of (a) 6.1±0.6 nm Fe36Pt64, (b) 5.8±0.7 nm Fe44Pt56, and (c) 5.1±0.7 nm Fe49Pt51 nanoparticles.
It was found that the crystal structure of these large FePt nanoparticles could be converted from fcc to L10
by annealing at 700C without significant coalescence.
[Ref.] Langmuir 2006, 22, 3485.
Magnetization curves of 5.1±0.7 nm Fe49Pt51 nanoparticles annealed under Ar+4%H2 at 300C for 1, 3, and 5 h.
[Ref.] J. Phys. Chem. C 2007, 111, 7231.
Ferromagnetic Spin Polarization in Au Nanoparticles
[Collaborator] Prof. Hidenobu Hori at Japan Advanced Institute of Science and Technology, Prof. Yoshiyuki Yamamoto at Akita University
(a) Particle size and (b) XMCD spectra of polyallylamine hydrochloride (PAAHC)-protected Au nanoparticles.
Owing to the element selectivity of XMCD, only the Au magnetization is explored. Magnetization of Au atoms as
estimated by XMCD shows a good agreement with results obtained by conventional magnetometry. This evidences intrinsic spin polarization in nanosized Au.
[Ref.] J. Magn. Magn. Mater. 2001, 226, 1910.; Physica B 2003, 329-333, 1183.; Phys. Rev. B 2004, 69, 174411.
J. Magn. Magn. Mater. 2004, 272, e1183.; Phys. Rev. Lett. 2004, 93, 116801.
(a) Particle size and (b) XMCD spectra of polyallylamine hydrochloride (PAAHC)-protected Au nanoparticles.
Owing to the element selectivity of XMCD, only the Au magnetization is explored. Magnetization of Au atoms as estimated by XMCD shows a good agreement with results obtained by conventional magnetometry. This evidences intrinsic spin polarization in nanosized Au.
[Ref.] J. Magn. Magn. Mater. 2001, 226, 1910.; Physica B 2003, 329-333, 1183.; Phys. Rev. B 2004, 69, 174411.
J. Magn. Magn. Mater. 2004, 272, e1183.; Phys. Rev. Lett. 2004, 93, 116801.
Conversion of Anisotropically Phase-Segregated Pd/γ-Fe2O3 Nanoparticles
into Exchange-Coupled L10-FePd/α-Fe Nanocomposite Magnets
[Collaborator] TOYOTA Motor Corporation Ltd.
Structural transformation of anisotropically phase-segregated Pd/γ-Fe2O3 nanoparticles
into fct-FePd/α-Fe nanocomposite magnets, which is induced by the interfacial atom diffusion.
[Ref.] JACS 2008, 130, 4210.
Structural transformation of anisotropically phase-segregated Pd/γ-Fe2O3 nanoparticles
into fct-FePd/α-Fe nanocomposite magnets, which is induced by the interfacial atom diffusion.
[Ref.] JACS 2008, 130, 4210.