Configuration and temperature dependence of magnetic damping in spin valves (original) (raw)
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Interlayer coupling in spin valves studied by broadband ferromagnetic resonance
Physical Review B, 2013
The magnetization dynamics of coupled and uncoupled spin valves with the structure NiFe (20 nm)/Cu(t Cu )/NiFe (20 nm)/IrMn (10 nm) is probed by broadband ferromagnetic resonance absorption measurements. The coupling intensity between the free and the pinned layers is tailored by varying the Cu thickness t Cu . Broadband spectra exhibited two resonant modes for each value of the applied field. It is observed that the coupling between NiFe layers modifies the amplitude of the absorption peaks and the shape of the dispersion relations for each mode, which becomes particularly distorted in the antiparallel magnetization state. The observed phenomena are well described by applying a semianalytical model that properly takes into account the coupling interactions and allows an efficient numerical calculation of the absorption peak amplitudes and the dispersion-relation shapes.
Time and frequency domain measurements of ferromagnetic resonance in small spin-valve
IEEE Transactions on Magnetics, 2000
Time and frequency domain magnetoresistance measurements of ferromagnetic resonance (FMR) in small spin-valve devices are presented along with comparisons to single-domain simulations. The measurements and simulations give consistent results for rotational motion with angular deviations of less than 30 from the easy axis. While the time and frequency domain measurements produce similar results for ideal devices in the linear regime, each technique provides different information as the devices become nonlinear and less ideal. Both time and frequency domain magnetoresistance measurements allow the study of FMR in considerably smaller magnetic structures than can be done with conventional techniques.
Physical Review B, 2012
Using time-resolved x-ray resonant magnetic scattering we report on the precessional dynamics of spin valve systems with parallel (P) and antiparallel (AP) orientation of the ferromagnetic layers separated by a nonmagnetic spacer layers. Previously we observed in Co/Cu/Ni 81 Fe 19 (Py) spin valve systems an increase of the magnetic damping parameter in Py with changing magnetization direction of Py and Co layers from P to AP orientation [Salikhov et al., Appl. Phys. Lett. 99, 092509 (2011)]. We attributed this finding to the configurational dependence of the spin pumping effect [Kim and Chappert, J. Magn. Magn. Mater. 286, 56 (2005)]. Here we extend our earlier findings by investigating the temperature dependence of the spin pumping effect and possible other causes for the configurational dependence of the damping parameter, such as domain wall induced coupling or magnetic dipole coupling. The main focus is on Co/Cu/Py trilayers and on Co 2 MnGe/V/Py trilayers with spin valve properties.
Temperature and field dependence of high-frequency magnetic noise in spin valve devices
Applied Physics Letters, 2003
The high-frequency noise of micrometer-dimension spin valve devices has been measured as a function of applied field and temperature. The data are well fit with single-domain noise models that predict that the noise power is proportional to the imaginary part of the transverse magnetic susceptibility. The fits to the susceptibility yield the ferromagnetic resonance ͑FMR͒ frequency and the magnetic damping parameter. The resonant frequency increases, from 2.1 to 3.2 GHz, as the longitudinal field varies from Ϫ2 to 4 mT and increases from 2.2 to 3.3 GHz as the temperature decreases from 400 to 100 K. The shift in the FMR frequency with temperature is larger than that expected from the temperature dependence of the saturation magnetization, indicating that other temperature-dependent anisotropy energies are present, in addition to the dominant magnetostatic energies. The measured magnetic damping parameter ␣ decreases from 0.016 to 0.006 as the temperature decreases from 400 to 100 K. The value of the damping parameter shows a peak as a function of longitudinal bias field, indicating that there is no strict correlation between the damping parameter and the resonant frequency.
Simulating device size effects on magnetization pinning mechanisms in spin valves
Journal of Applied Physics, 1996
The effects of magnetostatic interactions on the giant magnetoresistive ͑GMR͒ response of NiFe/ Cu/NiFe spin valves are studied using an analytical model. The model is applicable to devices small enough for the magnetic layers to exhibit single-domain behavior. Devices having lengths in the track-width direction of 10 m and interlayer separations of 4.5 nm are studied. Stripe heights are varied from 0.5 to 2 m. The magnetization of one magnetic layer is pinned by a transverse pinning field that is varied from 0 to 24 kA/m ͑300 Oe͒. GMR curves for transverse fields are calculated. At zero external field the magnetization of the layers shows a tendency to align themselves antiparallel in the transverse direction. This results in an offset from the ideal biasing of the device. Broadening of the curves due to shape anisotropy occurs with decreasing stripe height and increasing magnetic layer thickness, and the magnetization in the pinned layer becomes less stable.
Magnetization dynamics in spin-valve structures with spin pumping
Journal of Magnetism and Magnetic Materials, 2005
A dynamic coupling between the magnetic layers of a spin-valve structure can result from the exchange of spin currents pumped from the precessing magnetization of each layer. We show theoretically that such dynamic coupling can give rise to an effective damping for the free layer which depends on the spin-valve configuration and is sensitive to the bias field acting on the pinned layer.
Tunable magnetization relaxation in spin valves
2011
In spin values the damping parameters of the free layer are determined non-locally by the entire magnetic configuration. In a dual spin valve structure that comprises a free layer embedded between two pinned layers, the spin pumping mechanism, in combination with the angular momentum conservation, renders the tensor-like damping parameters tunable by varying the interfacial and diffusive properties. Simulations based on the Landau-Lifshitz-Gilbert phenomenology for a macrospin model are performed with the tensor-like damping and the relaxation time of the free layer magnetization is found to be largely dependent on while tunable through the magnetic configuration of the source-drain magnetization.
Spin-transfer dynamics in spin valves with out-of-plane magnetized CoNi free layers
Physical Review B, 2010
We have measured spin-transfer-induced dynamics in magnetic nanocontact devices having a perpendicularly magnetized Co/Ni free layer and an in-plane magnetized CoFe fixed layer. The frequencies and powers of the excitations agree well with the predictions of the single-domain model and indicate that the excited dynamics correspond to precessional orbits with angles ranging from zero to 90°as the applied current is increased at a fixed field. From measurements of the onset current as a function of applied field strength we estimate the magnitude of the spin torque asymmetry parameter ⌳ Ϸ 1.5. By combining these with spin torque ferromagnetic resonance measurements, we also estimate the spin-wave radiation loss in these devices.