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ABSTRACT: Fast precessional dynamics of magnetization are reported in very thin films of CoCrPt alloy with large perpendicular magnetic anisotropy. The films are fabricated with different substrate temperatures, and magnetization dynamics are investigated using time-resolved magneto-optical Kerr effect. The Kittel's equation well describes a dependency of magnetization precession frequency on an applied magnetic field direction for all the films, only when the field is relatively large. An inverse lifetime of magnetization precession, a counterpart of a line width in ferromagnetic resonance (FMR), depends strongly on the field direction even at the applied field of around 10 kOe. The Gilbert damping constant α is estimated to be ~0.05 for all the films using a model taking account of an influence of perpendicular magnetic anisotropy dispersion.
IEEE Transactions on Magnetics 11/2011; · 1.36 Impact Factor
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S Mizukami,
F Wu,
A Sakuma,
J Walowski, D Watanabe,
T Kubota,
X Zhang,
H Naganuma,
M Oogane,
Y Ando,
T Miyazaki
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ABSTRACT: Spin precession with frequencies up to 280 GHz is observed in Mn(3-δ)Ga alloy films with a perpendicular magnetic anisotropy constant K(u)∼15 M erg/cm(3). The damping constant α, characterizing macroscopic spin relaxation and being a key factor in spin-transfer-torque systems, is not larger than 0.008 (0.015) for the δ=1.46 (0.88) film. Those are about one-tenth of α values for known materials with large K(u). First-principles calculations well describe both low α and large K(u) for these alloys.
Physical Review Letters 03/2011; 106(11):117201. · 7.37 Impact Factor
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ABSTRACT: The influence of annealing temperature and film thickness on structural and magnetic properties of Mn<sub>2.5</sub> Ga films were investigated in this work. The annealing temperature of 400°C was found to be the optimum condition to obtain the films with high perpendicular magnetic anisotropy (PMA) (K<sub>u</sub> <sup>eff</sup> = 7.8 à 10<sup>6</sup> erg/cm<sup>3</sup>) and smooth surface (R<sub>a</sub> ¿ 0.15 nm). The PMA property was maintained in the 5 nm thick film, and deterioration of the PMA properties with decreasing film thickness can be ascribed to the tensile strain existed in the thin Mn<sub>2.5</sub> Ga films.
IEEE Transactions on Magnetics 07/2010; · 1.36 Impact Factor
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ABSTRACT: The magnetic properties of CoFeB buffered [Co(0.3 nm)Pd(x nm)]<sub>6</sub> multilayer films have been investigated. It is found that the magnetic properties of the multilayer depended on the Pd thickness and for thickness below 0.5 nm no perperdicular anisotropy is observed. Magnetization dynamics in perpendicularly magnetized CoFeB-[Co/Pd] multilayer films are investigated using time-resolved magneto-optical Kerr effect (TRMOKE). The variation of precession frequency with external magnetic field for different palladium thickness is quantitatively understood using the macrospin approximation of the Landau-Lifshitz-Gilbert equation of motion. The Gilbert damping constant ¿, in the range 0.04-0.1, varying with the palladium thickness is reported. The observed ¿ value is comparable to the damping coefficient of bulk Ni, and much lower than the reported values for perpendicularly magnetized films. The CoFeB buffer layer with in-plane anisotropy appears to significantly affect the precession frequency and thus the damping constant of the films.
IEEE Transactions on Magnetics 07/2010; · 1.36 Impact Factor
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ABSTRACT: To investigate the correlation between perpendicular magnetic anisotropy and intrinsic Gilbert damping, time-resolved magneto-optical Kerr effect was measured in Pt/Co(dCo)/Pt films. These films showed perpendicular magnetization at dCo = 1.0 nm and a perpendicular magnetic anisotropy energy Kueff that was inversely proportional to dCo. With an analysis based on the Landau–Lifshitz–Gilbert equation, the intrinsic Gilbert damping constant α was evaluated by parameter-fitting of frequency and lifetime expressions to experimental data of angular variations in spin precession frequency and life-times. The α values increased significantly with decreasing dCo but not inversely proportional to dCo.
Applied Physics Letters 04/2010; 96(15):152502-152502-3. · 3.84 Impact Factor
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ABSTRACT: Gilbert damping for the epitaxial Co <sub>2</sub> FeAl Heusler alloy films was investigated. Gilbert damping constant for the films was evaluated by analyzing the data of ferromagnetic resonance measured at the frequency of 2–20 GHz. Gilbert damping constant for the film without annealing was rather large, while it decreased remarkably with postannealing. Gilbert damping constant for the film annealed at 600 ° C was ≃0.001 . These behavior of Gilbert damping constant can be well explained by the fact that the density of states calculated from first principles decreases with increasing the degree of B2 order.
Journal of Applied Physics 05/2009; · 2.17 Impact Factor
