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1 Apr 2012

Volume 111, Issue 7, Articles (07xxxx)

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J. Appl. Phys. 111, 071101 (2012); http://dx.doi.org/10.1063/1.3694674 (23 pages)

Shunfeng Li and Andreas Waag
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back to top Micromagnetics, Magnetization Processes, Wall Dynamics, and Imaging

Random magnetization dynamics at elevated temperatures

I. Mayergoyz, G. Bertotti, C. Serpico, Z. Liu, and A. Lee

J. Appl. Phys. 111, 07D501 (2012); http://dx.doi.org/10.1063/1.3670510 (3 pages) | Cited 1 time

Online Publication Date: 8 February 2012

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Generalization of the classical Landau-Lifshitz equation for the case of magnetization dynamics at elevated temperatures is discussed. This generalization is based on the description of thermal bath effects by a jump-noise process, and it results in equations that describe magnetization dynamics when magnetization magnitude is not conserved.
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75.78.-n Magnetization dynamics
75.60.Ej Magnetization curves, hysteresis, Barkhausen and related effects

Static and dynamic magnetic properties of epitaxial Fe1.7Ge thin films grown on Ge(111)

M. Belmeguenai, D. Berling, G. Garreau, S. M. Chérif, D. Faurie, W. Seiler, and P. Moch

J. Appl. Phys. 111, 07D502 (2012); http://dx.doi.org/10.1063/1.3672396 (3 pages) | Cited 1 time

Online Publication Date: 23 February 2012

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We have studied the magnetic properties of thin epitaxial hexagonal Fe1.7Ge films grown on Ge(111) substrates by molecular beam epitaxy. For all samples, X-ray diffraction revealed an excellent epitaxy of the Fe1.7Ge films, with crystallographic [11math0] and [1math00] axes lying in the sample plane. The static magnetic properties were studied by Magneto-Optical Kerr Effect (MOKE) at room temperature. The dynamic magnetic properties at room temperature were investigated by Micro-Strip Ferromagnetic Resonance (MS-FMR). The frequency dependence of the spectra versus the orientation of the applied in-plane magnetic field shows that the contribution of the in-plane anisotropy to the magnetic energy density consists in two distinct terms exhibiting a twofold and a sixfold symmetry, respectively. The amplitude of the sixfold anisotropy constant is an increasing function of the film thickness. The observed angular dependence of the MOKE reduced remanent magnetization is described using a coherent rotation model. A good agreement is observed between the in-plane anisotropy values derived from MS-FMR and those obtained with MOKE Transverse Bias Initial Inverse Susceptibility and Torque data.
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75.70.Ak Magnetic properties of monolayers and thin films
68.55.A- Nucleation and growth
75.40.Cx Static properties (order parameter, static susceptibility, heat capacities, critical exponents, etc.)
75.40.Gb Dynamic properties (dynamic susceptibility, spin waves, spin diffusion, dynamic scaling, etc.)
75.30.Cr Saturation moments and magnetic susceptibilities
75.30.Gw Magnetic anisotropy

Anisotropy in collective precessional dynamics in arrays of Ni80Fe20 nanoelements

B. Rana, D. Kumar, S. Barman, S. Pal, R. Mandal, Y. Fukuma, Y. Otani, S. Sugimoto, and A. Barman

J. Appl. Phys. 111, 07D503 (2012); http://dx.doi.org/10.1063/1.3672402 (3 pages) | Cited 2 times

Online Publication Date: 23 February 2012

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The anisotropy in the collective precessional dynamics with the variation of azimuthal angle of the bias magnetic field is studied in arrays of permalloy (Ni80Fe20) nanoelements by an all-optical time-resolved Kerr microscope. When the nanoelements are very closely spaced (inter-element separation = 50 nm), a gradual transition from completely uniform collective regime to a completely non-collective regime is observed as the azimuthal angle varies from 0° to 45°. On the other hand, for inter-element separation of 100 nm, a non-uniform collective dynamics is observed at 0° and a non-collective dynamics is observed at 45° but no clear trend in the transition is observed.
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75.75.-c Magnetic properties of nanostructures
75.50.Bb Fe and its alloys
75.50.Tt Fine-particle systems; nanocrystalline materials
75.30.Gw Magnetic anisotropy

Amplification of spin waves by the spin Seebeck effect

E. Padrón-Hernández, A. Azevedo, and S. M. Rezende

J. Appl. Phys. 111, 07D504 (2012); http://dx.doi.org/10.1063/1.3673419 (3 pages)

Online Publication Date: 27 February 2012

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We observe amplification of spin-wave packets propagating along a film of single-crystal yttrium iron garnet (YIG) subject to a transverse temperature gradient. The spin waves are excited and detected with standard techniques used to study volume or surface magnetostatic waves in the 1–2 GHz frequency range. Amplification gains larger than 20 are observed in a YIG film heated by a current of 20 mA in a Pt layer in a simple YIG/Pt bilayer. The amplification is attributed to the action of a spin-transfer thermal torque acting on the magnetization that opposes the relaxation and which is created by spin currents generated through the spin Seebeck effect. The experimental data are interpreted with a spin-wave model.
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75.30.Ds Spin waves
75.50.Gg Ferrimagnetics
75.70.Ak Magnetic properties of monolayers and thin films
72.20.Pa Thermoelectric and thermomagnetic effects
75.60.Ej Magnetization curves, hysteresis, Barkhausen and related effects
81.40.Gh Other heat and thermomechanical treatments

Non-thermal excitation and control of magnetization in Fe/GaAs film by ultrafast laser pulses

Y. Gong, A. R Kutayiah, X. H. Zhang, J. H. Zhao, and Y. H. Ren

J. Appl. Phys. 111, 07D505 (2012); http://dx.doi.org/10.1063/1.3675158 (3 pages)

Online Publication Date: 29 February 2012

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We present our recent study of non-thermal excitation and coherent control of spin reorientation in 10-nm epitaxially grown Fe thin films by low-energy femtosecond laser pulses. The magnetization dynamics and hysteresis curves were recorded by pump-probe differential magnetic Kerr (DMK) spectroscopy using linearly polarized laser beams. A sharp switching in DMK signal is observed when we rotated the pump polarization. This result indicates a non-thermal origin of magnetization excitation and reorientation in Fe films. We reveal that spins can interact coherently with the polarization induced by the pulsed laser field in magnetic metals. Such opto-magnetic interactions are instantaneous and are only limited in time by the properties of laser pulses. Our results suggest the feasibility of ultrafast optical control of both the magnetization and the demagnetization responses in magnetic films.
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75.70.Ak Magnetic properties of monolayers and thin films
78.20.Ls Magneto-optical effects
75.60.-d Domain effects, magnetization curves, and hysteresis
68.55.A- Nucleation and growth
78.47.J- Ultrafast spectroscopy (<1 psec)
75.60.Ej Magnetization curves, hysteresis, Barkhausen and related effects

Mechanism analysis of ultrafast magnetic switching

J. M. Li, B. X. Xu, J. Zhang, and K. D. Ye

J. Appl. Phys. 111, 07D506 (2012); http://dx.doi.org/10.1063/1.3678487 (3 pages) | Cited 1 time

Online Publication Date: 9 March 2012

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The TbFeCo magneto-optical media with the coercivity of bigger than 1 kOe are used for the investigation of ultrafast magnetic switching and thermal demagnetization. The magnetic marks induced by 25 fs laser pulses with circular polarization have been observed. The thermal demagnetization spots are measured based on their digital images for the estimation of laser fluence. Based on the experimental parameters, a theoretical calculation for estimation of the maximum applicable effective magnetic field is conducted, where the 25 fs laser pulses with wavelength of 800 nm, NA of 0.6 and circular polarization is applied. The results show that, with the maximum applicable laser fluence, the effective magnetic field on the outer boundary of the laser spot defined by 1/e electrical field amplitude is about 0.52 kOe. It implies that the spin flips can be implemented by a small effective magnetic field, which can be explained with the analysis of spin temperature.
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75.60.Ej Magnetization curves, hysteresis, Barkhausen and related effects
78.20.Ls Magneto-optical effects
42.62.Cf Industrial applications

A quantum-mechanical relaxation model

R. Skomski, A. Kashyap, and D. J. Sellmyer

J. Appl. Phys. 111, 07D507 (2012); http://dx.doi.org/10.1063/1.3679605 (3 pages)

Online Publication Date: 13 March 2012

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The atomic origin of micromagnetic damping is investigated by developing and solving a quantum-mechanical relaxation model. A projection-operator technique is used to derive an analytical expression for the relaxation time as a function of the heat-bath and interaction parameters. The present findings are consistent with earlier research beyond the Landau-Lifshitz-Gilbert (LLG) equation and show that the underlying relaxation mechanism is very general. Zermelo’s recurrence paradox means that there is no true irreversibility in non-interacting nanoparticles, but the corresponding recurrence times are very long and can be ignored in many cases.
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46.40.Ff Resonance, damping, and dynamic stability
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