Browsing by Author "Fujiwara, H"

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    Biquadratic coupling effect on magnetoresistance response curves of spin valves with a synthetic antiferromagnet
    (American Institute of Physics, 2001-06-07) Zhang, K; Kai, T; Zhao, T; Fujiwara, H; Mankey, GJ; University of Alabama Tuscaloosa
    Both normal and inverse magnetoresistance (MR) response curves were observed for synthetic spin valves with the structure of Si(100)/Ru/Co(t(1))/Ru(0.7 nm)/Co(t(2))/Cu(3 nm)/Co(t(3))/Ru. Under the assumption of a coherent rotation of the magnetization in the three Co layers, the hysteresis loops, magnetization response, and MR response curves were calculated as a function of the parameters of the system. The parameters include antiferromagnetic coupling of Co(t(1)) and Co(t(2)) through Ru layer, a weak ferromagnetic coupling of Co(t(2)) and Co(t(3)) through Cu spacer, giant magnetoresistance of the Co/Cu/Co and Co/Ru/Co systems, and AMR contribution of each Co layer. The uniaxial anisotropy of each Co layer and a distribution of the coupling strength of Co(t(1))/Ru/Co(t(2)) were also included. To fit the experimental data well, it was necessary to include a biquadratic coupling in the Co(t(1))/Ru/Co(t(2)) trilayer. (C) 2001 American Institute of Physics.
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    Calibration of magnetic force microscopy using micron size straight current wires
    (American Institute of Physics, 2002-05-13) Liu, CX; Lin, K; Holmes, R; Mankey, GJ; Fujiwara, H; Jiang, HM; Cho, HS; University of Alabama Tuscaloosa; Seagate Technology
    A circuit with two long parallel micron size wires was fabricated by photolithography to calibrate magnetic force microscopy (MFM) tips. The tip phase shift increased as the tip scan height decreased. With the tip scan height kept constant, a linear relationship was found between the current amplitude and the phase shift of the tip at the center position of the two wires separation. The estimated magnetic moment of the tip was one order larger than its nominal value. The results imply that with better control over the fabrication process, the micron size straight wires can be used to calibrate MFM tips. (C) 2002 American Institute of Physics.
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    Magnetic properties of Co films on Cu/Si(110) and Cu(111)
    (American Physical Society, 2000-02-01) Maat, S; Umlor, MT; Orgassa, D; Cho, HS; Koshkina, O; Fujiwara, H; Mankey, GJ; University of Alabama Tuscaloosa
    The magnetic anisotropy of strained epitaxial Co films deposited on strained Cu(lll) on Si(110) and miscut Cu(lll) are reported. First, a Cu(lll) buffer layer with an in-plane strain is formed by epitaxial growth on Si(110). Co films deposited on the buffer layer develop a uniaxial anisotropy axis originating from the strain along the twofold axis of the Si(110) surface. The magnetic anisotropy of this film is compared to that of a Co film deposited on a miscut Cu(lll) single crystal with uniaxial step-induced anisotropy in the Co layer. The measured hysteresis loops are compared to hysteresis loops simulated within a Stoner-Wolfarth model with a varying fraction of uniaxial and triaxial anisotropies. The measurements and the model are in qualitative agreement and reveal uniaxial and triaxial anisotropies of the same order of magnitude for both systems.
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    Magnetocrystalline anisotropy in glancing angle deposited Permalloy nanowire arrays
    (AVS American Institute of Physics, 2005-06-28) Alouach, H; Fujiwara, H; Mankey, GJ; University of Alabama Tuscaloosa
    The magnetic anisotropy and properties of Permalloy (Ni80Fe20) nanowire arrays fabricated by glancing angle deposition with substrate rotation were studied. Epitaxial Cu nanowires, with the long axis textured along the Cu[111] crystallographic direction, were used as a seed layer to grow the Ni80Fe20 nanowires. The nanowires exhibit a strong Ni80Fe20[311] texture as shown by x-ray diffraction, with a Ni80Fe20[111] diffraction peak uniformly distributed about the wire's long axis normal to the substrate. Hysteresis loops taken at different angular orientations show that the magnetization saturates first along the wire's growth direction normal to the substrate. Samples with an aspect ratio of approximately one have equal in- and out-of-plane coercivity. At low aspect ratios (similar to 0.5-1.5), the angular dependence of the remanence shows that the maximum remanence lies on the surface of a cone with its axis along the substrate normal. A model which contains biaxial anisotropy with a symmetry axis normal to the substrate was found to qualitatively explain the characteristics of the observed hysteresis loops. An anisotropy constant on the order of 10(6) erg/cc is necessary to explain the observed behavior, which is much larger than that of bulk Ni80Fe20 (c) 2005 American Vacuum Society.
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    Optical interference in magneto-optic Kerr-effect measurements of magnetic multilayers
    (American Institute of Physics, 1999-01-15) Maat, S; Shen, L; Hou, C; Fujiwara, H; Mankey, GJ; University of Alabama Tuscaloosa
    Hysteresis loops of exchange-biased permalloy/Fe50Mn50/permalloy trilayers on glass were measured as a function of Fe50Mn50 and permalloy thicknesses with the longitudinal Kerr effect employing a coherent light source. Kerr signals originate from both permalloy layers and give a superposition of hysteresis loops. In vibrating sample magnetometer or looptracer measurements the contribution of a particular layer to a major hysteresis loop cannot be identified. With the Kerr setup presented it is possible to identify the contribution of each layer individually, since the finite optical path through the trilayer gives rise to optical attenuation and interference. For an increasing total thickness of the trilayer, the signal of the buried permalloy layer will become weaker due to attenuation. Kerr measurements of trilayers up to 40 nm show a superposition of two equally oriented loops. Major loops for trilayers of thickness greater than 40 nm show a superposition of two oppositely oriented hysteresis loops. The transition is dependent only on the total thickness of the trilayer, rather than the thickness of each individual layer. This unusual effect can be explained by the phase difference of the two Kerr signals. Additional measurements performed from the glass side of the samples and measurements of a Fe50Mn50/permalloy bilayer confirm that the sense of a hysteresis loop can change for a buried layer due to optical effects. (C) 1999 American Institute of Physics. [S0021-8979(99)06903-0].
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    Reconstruction of in-plane magnetization distributions from magnetic force microscope images
    (American Institute of Physics, 2001-06-07) Zhao, T; Fujiwara, H; Mankey, GJ; Hou, C; Sun, M; University of Alabama Tuscaloosa
    A three-step method is proposed for reconstructing the in-plane magnetization distribution from a magnetic force microscope (MFM) image. The magnetization distribution is initialized using some assumptions based on our knowledge about domain structures and MFM contrast mechanisms. Then the high-energy moment configurations, which are initialized based on linear variation assumption, are relaxed by performing a micromagnetic calculation using experimentally measured magnetic parameters. A section of a 360 degrees wall in a NiFe/NiO bilayer has been selected to illustrate the reconstruction procedures. It is shown that the method is effective in revealing the wall structure related to the MFM contrast. This method avoids problems caused by noise and nonunique solutions of the micromagnetic equations. (C) 2001 American Institute of Physics.