Samir Garzon

Temperature-dependent asymmetry of the nonlocal spin-injection resistance : Evidence for spin nonconserving interface scattering

We report nonlocal spin injection and detection experiments on mesoscopic Co-Al2O3-Cu spin valves. We have observed a temperature-dependent asymmetry in the nonlocal resistance between parallel and antiparallel configurations of the magnetic injector and detector. This strongly supports the existence of a nonequilibrium resistance that depends on the relative orientation of the detector magnetization and the nonequilibrium magnetization in the normal metal providing evidence for increasing interface spin scattering with temperature.

Coherent control of nanomagnet dynamics via ultrafast spin torque pulses

We demonstrate reliable manipulation of the magnetization dynamics of a precessing nanomagnet by precisely controlling the spin transfer torque on the subnanosecond time scale. Using a simple pulse shaping scheme consisting of two ultrafast spin torque pulses with variable amplitudes and delay, we demonstrate coherent control over the precessional orbits and the ability to tune the switching probability of a nanomagnet at room temperature and 77 K. Our measurements suggest that appropriately shaped spin transfer can be used to efficiently manipulate the orientation of a free layer nanomagnet, thus providing an alternative for spin torque driven spintronic devices.

Macrospin model to explain the absence of preswitching oscillations in magnetic tunnel junctions: Fieldlike spin-transfer torque

We show that the absence of pre-switching oscillations (“incubation delay”) in magnetic tunnel junctions can be explained within the macrospin model by a sizable field-like component of the spin-transfer torque. It is further suggested that measurements of the voltage dependence of tunnel junction switching time in the presence of external easy axis magnetic fields can be used to determine the magnitude and voltage dependence of the field-like torque.

Enhanced spin-dependent shot noise in magnetic tunnel barriers

We report the observation of enhanced spin-dependent shot noise in magnetic tunnel barriers, suggesting transport through localized states within the barrier. This is supported by the existence of negative magnetoresistance and structure in the differential conductance curves. A simple model of tunneling through two interacting localized states with spin-dependent tunneling rates is used to explain our observations.

Low frequency noise characteristics of submicron magnetic tunnel junctions

We report that low frequency (up to 200 kHz) noise spectra of magnetic tunnel junctions with areas 10cm at 10 Kelvin deviate significantly from the typical 1/f behavior found in large area junctions at room temperature. In most cases, a Lorentzian-like shape with characteristic time between 0.1 and 10 ms is observed, which indicates only a small number of fluctuators contribute to the measured noise. By investigating the dependence of noise on both the magnitude and orientation of an applied magnetic field, we find that magnetization fluctuations in both free and reference layers are the main sources of noise in these devices. At small fields, where the noise from the free layer is dominant, a linear relation between the measured noise and angular magnetoresistance susceptibility can be established.We report that low frequency (up to 200 kHz) noise spectra of magnetic tunnel junctions with areas ~10^{-10}cm^2

Effect of resistance feedback on spin torque-induced switching of nanomagnets

at 10 Kelvin deviate significantly from the typical 1/f behavior found in large area junctions at room temperature. In most cases, a Lorentzian-like shape with characteristic time between 0.1 and 10 ms is observed, which indicates only a small number of fluctuators contribute to the measured noise. By investigating the dependence of noise on both the magnitude and orientation of an applied magnetic field, we find that magnetization fluctuations in both free and reference layers are the main sources of noise in these devices. At small fields, where the noise from the free layer is dominant, a linear relation between the measured noise and angular magnetoresistance susceptibility can be established.

Alkanethiol induced changes in the magnetotransport properties of Co∕Au bilayers

Abstract In large magnetoresistance devices spin torque-induced changes in resistance can produce GHz current and voltage oscillations which can affect magnetization reversal. In addition, capacitive shunting in large resistance devices can further reduce the current, adversely affecting spin torque switching. Here, we simultaneously solve the Landau–Lifshitz–Gilbert equation with spin torque and the transmission line telegraphers equations to study the effects of resistance feedback and capacitance on magnetization reversal of both spin valves and magnetic tunnel junctions. While for spin valves parallel (P) to anti-parallel (AP) switching is adversely affected by the resistance feedback due to saturation of the spin torque, in low resistance magnetic tunnel junctions P–AP switching is enhanced. We study the effect of resistance feedback on the switching time of magnetic tunnel junctions, and show that magnetization switching is only affected by capacitive shunting in the pF range.

Synthesis and Properties of High-Quality InN Nanowires and Nanonetworks

We demonstrate that chemisorption of a dodecanethiol (C12H25SH) self-assembled monolayer on the surface of a Au film alters the coercivity Hc of an underlying Co film, as measured using the planar Hall effect. Changes in Hc occur over a time scale of hours, and only when the thiolated devices are biased with perpendicular magnetic fields. While vacuum-stored samples show larger changes in Hc than those stored under ambient conditions, sample-sample variability persists. We hypothesize that the coercivity shifts are caused by magnetostatic fields originating at the Au-thiol interface, which affect the Co domain structure during magnetization reversal.