Browsing by Author "Yu, CT"

Now showing 1 - 6 of 6
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    Dipolar induced, spatially localized resonance in magnetic antidot arrays
    (American Institute of Physics, 2003-11-03) Yu, CT; Pechan, MJ; Mankey, GJ; University System of Ohio; Miami University; University of Alabama Tuscaloosa
    Dipole induced, spatially localized ferromagnetic resonances (at 35 GHz) are observed in micron-sized antidot arrays in permalloy films fabricated with photolithography. All square (3 mum x 3 mum) and rectangular (3 mum x 4, 5, and 7 mum) array samples exhibit double resonances, with each resonance possessing uniaxial in-plane anisotropy. Interestingly, the easy axes of the two resonances are orthogonal in all cases. The magnitude of the induced dipolar anisotropy decreases with increasing rectangular aspect ratio for one of the resonances, but remains essentially constant for the other. Micromagnetic simulations reveal that the two resonance peaks are the consequence of a dipole field distribution producing two areas with distinctly different demagnetizing field patterns. (C) 2003 American Institute of Physics.
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    Effect of interface roughness on the exchange bias for NiFe/FeMn
    (American Institute of Physics, 2000-04-28) Liu, CX; Yu, CT; Jiang, HM; Shen, LY; Alexander, C; Mankey, GJ; University of Alabama Tuscaloosa
    The effect of interface roughness on exchange bias for NiFe/FeMn bilayers is investigated for polycrystalline films and epitaxial films. Three different systems were investigated: polycrystalline Ta (10 nm)/Ni80Fe20 (10nm)/Fe50Mn50 (20 nm) films on oxygen plasma-etched Si(100) or Cu/H-Si(100) and epitaxial Ni80Fe20 (10nm)/Fe60Mn40 (20 nm) films on Cu/H-Si(110). For films grown on plasma-etched substrates, as the etching time is increased, film roughness increases up to 12 nm. For the polycrystalline films grown on ultrathin Cu underlayers, x-ray diffraction shows the fcc (111) texture is greatly reduced as the thickness is increased. The epitaxial Cu/Si(110) buffer layer induces fcc (111) epitaxial growth and modifies the interface morphology. The dependence of exchange bias on roughness for each set of samples is explained in terms of a competition between the interfacial exchange coupling and the af uniaxial anisotropy. (C) 2000 American Institute of Physics. [S0021-8979(00)93708-3].
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    Lateral standing spin waves in permalloy antidot arrays
    (American Institute of Physics, 2004-05-25) Yu, CT; Pechan, MJ; Burgei, WA; Mankey, GJ; University System of Ohio; Miami University; University of Alabama Tuscaloosa
    Spin wave modes in permalloy antidot arrays have been investigated with ferromagnetic resonance at 9.7 GHz. In contrast to a quadratic dispersion expected for exchange standing spin waves, nearly linear relationship exists between the resonance field and mode index, and it can be approximately described by the dipole-dipole and exchange theory. Time-dependent micromagnetic simulations show that the spin wave modes are a result of lateral confinement from the vacant holes. Furthermore, the simulations visually reveal the existence of localized spin waves due to localized boundary conditions in antidots arrays. (C) 2004 American Institute of Physics.
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    Lattice symmetry and magnetization reversal in micron-size antidot arrays in Permalloy film
    (American Institute of Physics, 2002-05-13) Vavassori, P; Gubbiotti, G; Zangari, G; Yu, CT; Yin, H; Jiang, H; Mankey, GJ; Consiglio Nazionale delle Ricerche (CNR); Istituto Nazionale per la Fisica della Materia (INFM-CNR); University of Ferrara; University of Alabama Tuscaloosa
    The magnetization reversal in four arrays of micron-size circular holes (antidots) in a Permalloy film has been studied by means of quantitative magneto-optic Kerr vector magnetometry and magnetic force microscopy. The primitive antidot meshes of the arrays investigated here can be classified as square, rectangular, hexagonal, and oblique. The vector magnetometry data show that the hole arrays induce a magnetic anisotropy completely different from that of the unpatterned film, with new hard axes along the directions connecting nearest neighboring holes. Also the coercive field is strongly affected by the pattern. The results of the vector magnetometry analysis indicate that the reversal process takes place through a collective and periodic domain nucleation and expansion process. The domain structure in the remanent state has been investigated by magnetic force microscopy imaging. The images display well-defined domain structures, which are periodic and commensurate with the holes array. (C) 2002 American Institute of Physics.
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    The magnetic anisotropy and domain structure of permalloy antidot arrays
    (American Institute of Physics, 2000-04-28) Yu, CT; Jiang, H; Shen, L; Flanders, PJ; Mankey, GJ; University of Alabama Tuscaloosa
    The magnetic properties of antidot arrays in permalloy films were studied using magnetic force microscopy (MFM), the magneto-optical Kerr effect (MOKE), and torque magnetometry. New observations of the magnetic domain structure, magnetization reversal process, and magnetic anisotropy are presented. Magnetic domains were imaged during magnetization reversal to identify the magnetization switching processes with the field applied along the diagonal and the edge of the hole mesh. A four-fold anisotropy related to the confinement of domains by the hole mesh was observed by torque magnetometry at intermediate fields. (C) 2000 American Institute of Physics. [S0021-8979(00)74508-7].
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    Magnetic properties of uniaxial synthetic antiferromagnets for spin-valve applications
    (American Physical Society, 2005-03-25) Zhao, ZY; Mani, P; Mankey, GJ; Gubbiotti, G; Tacchi, S; Spizzo, F; Lee, WT; Yu, CT; Pechan, MJ; Consiglio Nazionale delle Ricerche (CNR); Istituto Nazionale per la Fisica della Materia (INFM-CNR); Sapienza University Rome; University of Perugia; University of Ferrara; United States Department of Energy (DOE); Oak Ridge National Laboratory; Spallation Neutron Source; University System of Ohio; Miami University; University of Alabama Tuscaloosa
    The magnetic properties of synthetic antiferromagnetic Si(100)/Ta (5 nm)/Co(t(1))/Ru (0.65 nm)/Co(t(2))/Ta (10 nm) with an obliquely sputtered Ta underlayer are reported as a function of the top Co layer thickness, t(2). The morphological origin of the large in-plane magnetic anisotropy created by the obliquely sputtered Ta underlayer is revealed by atomic force microscopy. The magnetic anisotropy of the base Co layer is determined by measuring the dispersion of the Damon-Eshbach spin-wave mode with Brillouin light scattering. Ferromagnetic resonance measurements and hysteresis loops reveal that both the anisotropy and the saturation field of the trilayer system decrease with increasing top Co layer thickness. The dependence of the saturation field on layer thickness is fitted to an energy minimization equation that contains both bilinear and biquadratic exchange coupling constants. Magnetoresistance and polarized neutron reflectometry results both confirm that the magnetic reversal process of the system is through magnetic domain formation followed by rotation.