High-frequency measurements of spin-valve films and devices (invited) (original) (raw)
2003, Journal of Applied Physics
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.
Related papers
High-frequency noise measurements in spin-valve devices
Journal of Vacuum Science & Technology A: Vacuum, Surfaces, and Films, 2003
High-frequency magnetic noise in magnetoresistive devices being developed for read-sensor and magnetic random access memory applications may present fundamental limitations on the performance of submicrometer magnetic devices. High-frequency magnetic noise ͑HFN͒ arises from intrinsic thermal fluctuations of the device magnetization. High-frequency noise spectroscopy provides a powerful tool to characterize the dynamics and response of small multilayer magnetic devices. In this study, the noise characteristics of micrometer-dimension spin valves have been investigated at frequencies in the range 0.1-6 GHz. At frequencies below this range 1/f noise dominates. HFN measurements, as a function of bias current and longitudinal magnetic field, are obtained for IrMn exchange-biased spin valves using a 50 GHz spectrum analyzer, low-noise amplifier, and a microwave probing system. The magnetic noise is obtained by taking the difference between the noise spectrum of the device in a saturated and unsaturated state. The data can be fit to simple models that predict the noise power to be proportional to the imaginary part of the free-layer magnetic susceptibility. There are some important differences between the high-frequency noise measurements and direct measurements of the device susceptibility ͑both at the device and wafer level͒. The noise measurements show a smaller damping parameter ͑a smaller ferromagnetic resonance linewidth͒ and additional features due to the presence of nonuniform modes.
Configuration and temperature dependence of magnetic damping in spin valves
Journal of Applied Physics, 2011
Using vector-analyzer ferromagnetic resonance, we have studied the microwave susceptibility of a Py=Co=Cu=Co=MnIr spin valve over a large temperature range (5-450 K) and as a function of the magnetic configuration. An effective magnetization and Gilbert damping constant of 1.1 T and 0.021, respectively, are found for the permalloy free layer, with no discernible variation in temperature observed for either quantities. In contrast, the pinned layer magnetization is reduced by heating, and the exchange bias collapses near a temperature of 450 K. The ferromagnetic resonance linewidth of the free layer increases by 500 MHz when the layer magnetizations are aligned in antiparallel, which is attributed to a configuration-dependent contribution to the damping from spin pumping effects. V
Thermal magnetization noise in submicrometer spin valve sensors
Journal of Applied Physics, 2003
With decreasing device dimensions thermal fluctuations may ultimately limit the performance of spin valve sensors. Using finite element micromagnetic simulations, we investigate thermal magnetization noise in submicrometer soft magnetic sensor elements within the framework of Langevin simulations. Local random thermal fluctuations lead to a collective motion of the magnetization. The magnetization precesses in the end domains leading to an oscillation of the total magnetization parallel to the long axes with an amplitude in the order of 0.1 M s at 350 K. The noise power increases linearly with temperature. Irrespective of the bias field, the time averaged total magnetization parallel to the long axes decays approximately by 0.01 M s as the temperature is raised by 100 K.
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.
Applied Physics A, 2013
The authors have investigated the possibility of utilizing spin waves for inter-and intra-chip communications, and as logic elements using both simulations and experimental techniques. Through simulations it has been shown that the decay lengths of magnetostatic spin waves are affected most by the damping parameter, and least by the exchange stiffness constant. The damping and dispersion properties of spin waves limit the attenuation length to several tens of microns. Thus, we have ruled out the possibility of inter-chip communications via spin waves. Experimental techniques for the extraction of the dispersion relationship have also been demonstrated, along with experimental demonstrations of spin wave interference for amplitude modulation. The effectiveness of spin wave modulation through interference, along with the capability of determining the spin wave dispersion relationships electrically during manufacturing and testing phase of chip production may pave the way for using spin waves in analog computing wherein the circuitry required for performing similar functionality becomes prohibitive.
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.
Loading Preview
Sorry, preview is currently unavailable. You can download the paper by clicking the button above.