Showing papers by "Ilya Krivorotov published in 2016"

Giant spin-torque diode sensitivity in the absence of bias magnetic field.

Abstract: Microwave detectors based on the spin-torque diode effect are among the key emerging spintronic devices By utilizing the spin of electrons in addition to charge, they have the potential to overcome the theoretical performance limits of their semiconductor (Schottky) counterparts However, so far, practical implementations of spin-diode microwave detectors have been limited by the necessity to apply a magnetic field Here, we demonstrate nanoscale magnetic tunnel junction microwave detectors, exhibiting high-detection sensitivity of 75,400 mV mW(-1) at room temperature without any external bias fields, and for low-input power (micro-Watts or lower) This sensitivity is significantly larger than both state-of-the-art Schottky diode detectors and existing spintronic diodes Micromagnetic simulations and measurements reveal the essential role of injection locking to achieve this sensitivity performance This mechanism may provide a pathway to enable further performance improvement of spin-torque diode microwave detectors

Experimental Demonstration of xor Operation in Graphene Magnetologic Gates at Room Temperature

Abstract: Graphene is the wonder material hoped to enable the energy-efficient spin-based information processing that could replace today's electronics. Actually making working devices from this stuff, however, is not trivial. This study presents a milestone in harnessing spins in graphene for computation: The authors have produced one of the building blocks needed to make spintronic integrated circuits.

Spin caloritronic nano-oscillator

Abstract: Energy loss due to ohmic heating is a major bottleneck limiting down-scaling and speed of nano-electronic devices, and harvesting ohmic heat for signal processing is a major challenge in modern electronics. Here we demonstrate that thermal gradients arising from ohmic heating can be utilized for excitation of coherent auto-oscillations of magnetization and for generation of tunable microwave signals. The heat-driven dynamics is observed in $\mathrm{Y_{3}Fe_{5}O_{12}/Pt}$ bilayer nanowires where ohmic heating of the Pt layer results in injection of pure spin current into the $\mathrm{Y_{3}Fe_{5}O_{12}}$ layer. This leads to excitation of auto-oscillations of the $\mathrm{Y_{3}Fe_{5}O_{12}}$ magnetization and generation of coherent microwave radiation. Our work paves the way towards spin caloritronic devices for microwave and magnonic applications.

Temperature dependence of perpendicular magnetic anisotropy in CoFeB thin films

Abstract: We study perpendicular magnetic anisotropy in thin films of Ta/Co20Fe60B20/MgO by ferromagnetic resonance and find a linear temperature dependence for the first and second order uniaxial terms from 5 to 300 K. Our data suggest the possible hybridization of Fe-O orbitals at the CoFeB/MgO interface for the origin of the first order anisotropy. However, we also find that non-interfacial contributions to the anisotropy are present. An easy-cone anisotropy is found for the entire temperature range in the narrow region of film thicknesses around the spin reorientation transition 1.2–1.35 nm.

Magnetic anisotropy, damping, and interfacial spin transport in Pt/LSMO bilayers

Abstract: We report ferromagnetic resonance measurements of magnetic anisotropy and damping in epitaxial La0.7Sr0.3MnO3 (LSMO) and Pt capped LSMO thin films on SrTiO3 (001) substrates. The measurements reveal large negative perpendicular magnetic anisotropy and a weaker uniaxial in-plane anisotropy that are unaffected by the Pt cap. The Gilbert damping of the bare LSMO films is found to be low α = 1.9(1) × 10−3, and two-magnon scattering is determined to be significant and strongly anisotropic. The Pt cap increases the damping by 50% due to spin pumping, which is also directly detected via inverse spin Hall effect in Pt. Our work demonstrates efficient spin transport across the Pt/LSMO interface.

Material parameters of perpendicularly magnetized tunnel junctions from spin torque ferromagnetic resonance techniques

Abstract: The exchange-stiffness and saturation magnetization for the CoFeB based free layer of perpendicularly magnetized tunnel junctions (MTJs) were determined by performing spin torque ferromagnetic resonance measurements over a range of different sized devices. The field dispersion of several low-frequency spin wave modes shows a size dependent shift in the resonance frequencies due to the change in the lateral confinement and demagnetization field. From the effect of the demagnetizing field, the free layer saturation magnetization is estimated to be ∼800 emu/cm3 and its total perpendicular anisotropy field ∼12 kOe. From the separation of spin wave dispersion relations, an exchange stiffness value of 0.35 eV A2 is extracted.

Wireless current sensing by near field induction from a spin transfer torque nano-oscillator

Abstract: We demonstrate that spin transfer torque nano-oscillators (STNO) can act as wireless sensors for local current. The STNO acts as a transducer that converts weak direct currents into microwave field oscillations that we detect using an inductive coil. We detect direct currents in the range of 300–700 μA and report them wirelessly to a receiving induction coil at distances exceeding 6.5 mm. This current sensor could find application in chemical and biological sensing and industrial inspection.

Highly Textured IrMn3(111) Thin Films Grown by Magnetron Sputtering

Abstract: Non-collinear spin ground states in metallic antiferromagnets can give rise to anomalous Hall effect, which enables magnetic state readout in antiferromagnetic spintronic devices. Here we report growth of highly textured films of a non-collinear antiferromagnet IrMn3 on MgO(111) substrates by magnetron sputtering. The films consist of epitaxial (111) twin domains rotated by 60 degrees within the film plane. The films exhibit partial L12 ordering that supports the non-collinear T1 spin structure predicted to give rise to anomalous Hall effect. An MgO buffer layer evaporated onto the substrate increases the L12 order parameter from 0.4 to 0.75 but destroys the (111) crystallographic texture.

Optical investigation of radiation induced conductivity changes in STT-RAM cells

Abstract: Plasmonic defect spectroscopy of STT-RAMs under high energy radiation is proposed here. We show that engineered constellation designs of the STT-RAMs can be used to understand radiation defects by measuring optical reflectivity, diffraction, or absorption.