Masato Takenaka

National Institute of Advanced Industrial Science and Technology, Tsukuba, Ibaraki, Japan

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Publications (6)11.51 Total impact

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    ABSTRACT: In this study, the deposition pressure dependence of the compositional ratio, magnetic domain structure, and perpendicular magnetic anisotropy (PMA) of B-containing PrFe- and PrCo-based films, which are rare-earth–transition-metal (RE–TM) films, was investigated. PrFe- and PrCo-based films were fabricated by magnetron sputtering. The film compositions were controlled in a wide range by varying the deposition pressure. On the basis of experimental results, the residual stress of the films was considered to be the possible origin of their PMA. The films showed strong magneto-optical effects over the entire wavelength range of 300–750nm. Because of the excellent magnetic and magneto-optical (MO) properties of the films, they have high potential for MO applications at wavelengths of red and blue lasers.
    Journal of Magnetism and Magnetic Materials 04/2010; 322(8):900-908. DOI:10.1016/j.jmmm.2009.11.022 · 1.97 Impact Factor
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    ABSTRACT: Thin films of Pr12.5Fe77.5B10 have been successfully fabricated on thermally oxidized Si substrates by magnetron sputtering deposition. The microstructure and magnetic properties were altered by controlling the substrate temperature during the deposition. The stripe magnetic domain structure arising from the perpendicular magnetic anisotropy was observed by a magnetic force microscope in the uniform amorphous film deposited at room temperature. In contrast, the exchange coupled magnetic domain leading to the magnetic hardening was evidenced in the film deposited at 600 °C. These results suggest the great possibility of Pr12.5Fe77.5B10 thin films for electromagnetically actuated microelectromechanical applications.
    Journal of Physics D Applied Physics 12/2008; 42(2):025004. DOI:10.1088/0022-3727/42/2/025004 · 2.72 Impact Factor
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    ABSTRACT: We propose a reactive ion etching (RIE) process of an L10-FePt film which is expected as one of the promising materials for the perpendicular magnetic recording media. The etching was carried out using an inductively coupled plasma (ICP) RIE system and an etching gas combination of CH4/O2/NH3 was employed. The L10-FePt films were deposited on (1 0 0)-oriented MgO substrates using a magnetron sputtering system. The etching masks of Ti were patterned on the FePt films lithographically. The etch rates of ∼16 and ∼0 nm/min were obtained for the FePt film and the Ti mask, respectively. The atomic force microscopy (AFM) analyses provided the average roughness (Ra) value of 0.95 nm for the etched FePt surface, that is, a very flat etched surface was obtained. Those results show that the highly selective RIE process of L10-FePt was successfully realized in the present study.
    Applied Surface Science 09/2008; 254(23):7918-7920. DOI:10.1016/j.apsusc.2008.03.155 · 2.71 Impact Factor
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    ABSTRACT: The temperature dependence of the exchange bias has been investigated in Fe films deposited on the Si substrates with the native oxidize layer. A crossover from negative to positive exchange bias has been observed with increasing temperature at 30 K, accompanied with the maximum of the coercivity. This effect could be understood as a result of the exchange coupling between the ferromagnetic Fe film and the spin-glasslike Fe oxides particles formed spontaneously at the interface, where the direction of their end spins controls the sign of exchange bias.
    Journal of Applied Physics 05/2008; 103(9):093914-093914-4. DOI:10.1063/1.2917087 · 2.18 Impact Factor
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    ABSTRACT: The crystal structure and exchange bias effect in Fe films deposited on Si(100) substrates have been investigated. X-ray diffraction and fluorescence-extended X-ray absorption fine structure measurements reveal that the as-deoposited Fe films are polycrystalline with a preferred (110) texture. In addition, we observe a shift in the magnetic hysteresis loop of Fe films deposited on Si (100) where there is existance of a thin oxidized layer. By comparison, for Fe film deposited on Si(100) lacking the oxidized layer, it does not exhibit any features of shift in the magnetic hysteresis loop. We postulate the effect results from a coupling between the ferromagnetic Fe film and the antiferromagnetic Fe oxide that forms spontaneously in the interface. (© 2008 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)
    physica status solidi (c) 12/2007; 4(12):4352 - 4355. DOI:10.1002/pssc.200777415
  • H. Kuramochi · T. Manago · D. Koltsov · M. Takenaka · M. Iitake · H. Akinaga ·
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    ABSTRACT: The advantage of the CoFe-coated carbon nanotube (CNT) probes in a magnetic force microscope (MFM) is verified on in-plane magnetized soft magnetic materials. CoFe-coated CNT, standard and low-moment MFM probes were used to observe closure domains in square and rectangular Permalloy elements. The perturbative effect of the CNT–MFM probe was far less than that of a standard MFM probe. Domain walls were clearly observed as a pair of dark and bright lines which was in agreement with the micromagnetic simulations. The vortex core was also clearly observed using the CNT–MFM probes.
    Surface Science 11/2007; 601(22):5289-5293. DOI:10.1016/j.susc.2007.04.222 · 1.93 Impact Factor