arXiv subjects

Sergei Urazhdin

Publications and source records attributed to Sergei Urazhdin.

45 records · Page 3Linked to original sources

arXiv2015

Dynamical Skyrmion State in a Spin Current Nano-Oscillator with Perpendicular Magnetic Anisotropy

We study the spectral characteristics of spin current nano-oscillators based on the Pt/[Co/Ni] magnetic multilayer with perpendicular magnetic anisotropy. By varying the applied magnetic field and current, both localized and propagating spin wave modes of the oscillation are achieved. At small fields, we observe an abrupt onset of the modulation sidebands. We use micromagnetic simulations to identify this state as a dynamical magnetic skyrmion stabilized in the active device region by spin current injection, whose current-induced dynamics is accompanied by the gyrotropic motion of the core due to the skew deflection. Our results demonstrate a practical route for controllable skyrmion manipulation by spin current in magnetic thin films.

cond-mat.mtrl-sci↗

arXiv2010

Parametric excitation of a magnetic nanocontact by a microwave field

We demonstrate that magnetic oscillations of a current-biased magnetic nanocontact can be parametrically excited by a microwave field applied at twice the resonant frequency of the oscillation. The threshold microwave amplitude for the onset of the oscillation decreases with increasing bias current, and vanishes at the transition to the auto-oscillation regime. The parametrically excited oscillation mode is the same as the one in the auto-oscillation regime, enabling studies of both the passive and the active dynamics of the oscillator. Theoretical analysis shows that measurements of parametric excitation provide quantitative information about the relaxation rate, the spin transfer efficiency, and the nonlinearity of the nanomagnetic system.

cond-mat.mtrl-sci↗

arXiv2008

Current-induced reversal in magnetic nanopillars passivated by silicon

We demonstrate that magnetic multilayer nanopillars can be efficiently protected from oxidation by coating with silicon. Both the protected and the oxidized nanopillars exhibit an increase of reversal current at cryogenic temperatures. However the magnetic excitation onset current increases only in the oxidized samples. We show that oxidized nanopillars exhibit anomalous switching statistics at low temperature, providing a simple test for the quality of magnetic nanodevices.

cond-mat.mtrl-sci↗

arXiv2008

Current-Induced Dynamics in Almost Symmetric Magnetic Nanopillars

Magnetic nanodevices usually include a free layer whose configuration can be changed by spin-polarized current via the spin transfer effect, and a fixed reference layer. Here, we demonstrate that the roles of the free and the reference layers interchange over a small range of their relative thicknesses. Precession of both layers can be induced by spin transfer in symmetric devices, but the dynamics of one of the layers is rapidly suppressed in asymmetric devices. We interpret our results in terms of the dynamical coupling between magnetic layers due to spin transfer.

cond-mat.mtrl-sci↗

arXiv2008

Dynamical Regimes Induced by Spin Transfer in Magnetic Nanopillars

We demonstrate the predicted out-of-plane precession induced by spin transfer in magnetic nanostructures with in-plane magnetic field. We show that other magnetic excitations have a significant effect on the stability of the out-of plane precession, making it extremely sensitive to the orientation of the applied magnetic field. The data are supported with micromagnetic simulations. Our results elucidate the relation between the excitation spectrum and the specific dynamical behaviors of nanoscale magnets.

cond-mat.mtrl-sci↗

arXiv2008

Relationship between granularity of antiferromagnet and exchange bias

We studied exchange bias in magnetic multilayers incorporating antiferromagent CoO doped with up to 35 atomic percent of Pt. The exchange bias increased with doping in epitaxial films, but did not significantly change in polycrystalline films at the lowest measured temperature of 5 K, and decreased at higher temperatures. We explain our results by the increased granularity of the doped antiferromagnetic films, resulting in simultaneous enhancement of the uncompensated spin density and reduction of the magnetic stability of antiferromagnetic grains.

cond-mat.mtrl-sci↗

arXiv2008

Effect of spin diffusion on spin torque in magnetic nanopillars

We present systematic magnetoelectronic measurements of magnetic nanopillars with different structures of polarizing magnetic layers. The magnetic reversal at small magnetic field, the onset of magnetic dynamics at larger field, and the magnetoresistance exhibit a significant dependence on the type of the polarizing layer. We performed detailed quantitative modeling showing that the differences can be explained by the effects of spin-dependent electron diffusion.

cond-mat.mtrl-sci↗

arXiv2008

Thermal Dynamics in Symmetric Magnetic Nanopillars Driven by Spin Transfer

We study the effects of spin transfer on thermally activated dynamics of magnetic nanopillars with identical thicknesses of the magnetic layers. The symmetric nanopillars exhibit anomalous dependencies of switching statistics on magnetic field and current. We interpret our data in terms of simultaneous current-induced excitation of both layers. We also find evidence for coupling between the fluctuations of the layers due to the spin transfer.

cond-mat.mtrl-sci↗

arXiv2007

Effect of Polarized Current on the Magnetic State of Antiferromagnet

We provide evidence for the effects of spin polarized current on a nanofabricated antiferromagnet incorporated into a spin-valve structure. Signatures of current-induced effects include bipolar steps in differential resistance, current-induced changes of exchange bias correlated with these steps, and deviations from the statistics expected for thermally activated switching of spin valves. We explain our observations by a combination of spin torque exerted on the interfacial antiferromagnetic moments, and electron-magnon scattering in antiferromagnet.

cond-mat.mtrl-sci↗