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15 May 2003

Volume 93, Issue 10, pp. 5855-8792

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Dynamic exchange coupling and Gilbert damping in magnetic multilayers (invited)

Yaroslav Tserkovnyak, Arne Brataas, and Gerrit E. W. Bauer

J. Appl. Phys. 93, 7534 (2003); http://dx.doi.org/10.1063/1.1538173 (5 pages) | Cited 6 times

Online Publication Date: 9 May 2003

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We theoretically study dynamic properties of thin ferromagnetic films in contact with normal metals. Moving magnetizations cause a flow of spins into adjacent conductors, which relax by spin flip, scatter back into the ferromagnet, or are absorbed by another ferromagnet. Relaxation of spins outside the moving magnetization enhances the overall damping of the magnetization dynamics in accordance with the Gilbert phenomenology. Transfer of spins between different ferromagnets by these nonequilibrium spin currents leads to a long-ranged dynamic exchange interaction and collective excitation modes. Our predictions agree well with recent ferromagnetic-resonance experiments on ultrathin magnetic films. © 2003 American Institute of Physics.
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75.70.Cn Magnetic properties of interfaces (multilayers, superlattices, heterostructures)
75.30.Et Exchange and superexchange interactions
75.40.Gb Dynamic properties (dynamic susceptibility, spin waves, spin diffusion, dynamic scaling, etc.)
75.60.Ej Magnetization curves, hysteresis, Barkhausen and related effects

High-frequency measurements of spin-valve films and devices (invited)

Shehzaad Kaka, John P. Nibarger, Stephen E. Russek, N. A. Stutzke, and S. L. Burkett

J. Appl. Phys. 93, 7539 (2003); http://dx.doi.org/10.1063/1.1558257 (6 pages) | Cited 9 times

Online Publication Date: 9 May 2003

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High-frequency measurements of spin-valve films and devices, made using several different measurement techniques, are presented and compared. Pulsed inductive measurements were made on sheet films and provide insight into the intrinsic dynamical properties of the component films and multilayer stacks. The damping parameter, in the completed spin-valve stack, is larger than in the constituent films. Direct time and frequency domain measurements of the dynamical response of micrometer-size spin-valve devices, made using high-bandwidth magnetoresistance techniques, showed damping parameters comparable to these measured on spin-valve sheet films. The small-angle magnetization response was also determined by high-frequency magnetic noise measurements. The damping parameters were smaller than those obtained by direct susceptibility measurements. The device-level measurements show a different dependence of the damping parameter on the easy-axis field as compared to sheet-level measurements. In addition to the uniform rotation mode, other peaks can be observed in the noise spectra that correspond to fluctuation modes arising from the micromagnetic structure. Electrical device measurements have much greater sensitivity than other high-frequency magnetic measurement techniques, which allow the direct observation of magnetization motion in submicrometer elements without averaging. This technique is used to directly examine thermally activated events and nonrepetitive dynamical motions. © 2003 American Institute of Physics.
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75.47.De Giant magnetoresistance
75.70.Cn Magnetic properties of interfaces (multilayers, superlattices, heterostructures)
75.60.Ej Magnetization curves, hysteresis, Barkhausen and related effects
76.50.+g Ferromagnetic, antiferromagnetic, and ferrimagnetic resonances; spin-wave resonance
75.30.Cr Saturation moments and magnetic susceptibilities

Role of dynamic exchange coupling in magnetic relaxations of metallic multilayer films (invited)

B. Heinrich, G. Woltersdorf, R. Urban, and E. Simanek

J. Appl. Phys. 93, 7545 (2003); http://dx.doi.org/10.1063/1.1543852 (6 pages) | Cited 15 times

Online Publication Date: 9 May 2003

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The relaxation processes were investigated by ferromagnetic resonance (FMR) using magnetic single, Au/Fe/GaAs(001), and double layer, Au/Fe/Au/Fe/GaAs(001), structures prepared by molecular beam epitaxy. These structures provided an excellent opportunity to investigate nonlocal damping which is caused by spin transport across a nonmagnetic spacer. In the double layer structures thin Fe layers F1 were separated from a second thick Fe layer F2 by a Au(001), normal metal spacer. The interface magnetic anisotropies separated the FMR fields of F1 and F2 by a big margin which allowed us to investigate FMR in F1 while F2 had a negligible angle of precession. The main result is that the ultrathin Fe films in magnetic double layers acquire a nonlocal interface Gilbert damping. Several mechanisms have been put forward to explain the nonlocal damping. A brief review of each mechanism will be presented. They will be compared with the experimental results allowing one to critically assess their applicability and strength. It will be shown that the precessing layers act as spin pumps and spin sinks. This concept was tested by investigating the FMR linewidth around an accidental crossover of the resonance fields for the layers F1 and F2. © 2003 American Institute of Physics.
Show PACS
75.70.Cn Magnetic properties of interfaces (multilayers, superlattices, heterostructures)
75.50.Bb Fe and its alloys
75.30.Et Exchange and superexchange interactions
76.50.+g Ferromagnetic, antiferromagnetic, and ferrimagnetic resonances; spin-wave resonance
72.25.Mk Spin transport through interfaces
75.30.Gw Magnetic anisotropy
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