Jeffrey R. Childress

Nanoscale magnetic field detection using a spin torque oscillator

Magnetic field detection with extremely high spatial resolution is crucial to applications in magnetic storage, biosensing, and magnetic imaging. Here, we present the concept of using a spin torque oscillator (STO) to detect magnetic fields by measuring the frequency of the oscillator. This sensors performance relies predominantly on STO properties such as spectral linewidth and frequency dispersion with magnetic field, rather than signal amplitude as in conventional magnetoresistive sensors, and is shown in measured devices to achieve large signal to noise ratios. Using macrospin simulations, we describe oscillator designs for maximizing performance, making spin torque oscillators an attractive candidate to replace more commonly used sensors in nanoscale magnetic field sensing and future magnetic recording applications.

Magnetotransport properties and spin-torque effects in current perpendicular to the plane spin valves with Co-Fe-Al magnetic layers

The magnetotransport properties of current perpendicular to the plane giant magnetoresistive spin valves utilizing (CoxFe100−x)100−yAly alloys are investigated over a wide alloy composition range. (Co50Fe50)75Al25 is determined to be the approximate alloy composition that maximizes magnetoresistance. An increase in magnetoresistance from 1.7% for spin valves with standard Co50Fe50 to 3.3% for spin valves with (Co50Fe50)75Al25 is observed when substituting the same “magnetic” thickness in both the reference and the free layers. The spin-diffusion length for (Co50Fe50)75Al25 is determined to be less than approximately 35A. Spin-torque measurements show that the spin-torque current density threshold is lower in CoFeAl spin valves compared to standard CoFe spin valves.

Experimental test of an analytical theory of spin-torque-oscillator dynamics

We make measurements of power spectral density of the microwave voltage emitted by a spin-torque-nano-oscillator (STNO) consisting of a

Current perpendicular to the plane spin-valves with CoFeGe magnetic layers

{\text{Ni}}_{86}{\text{Fe}}_{14}

Localized magnetic modification of permalloy using Cr+ ion implantation

nanowire free layer and a

Suppression of spin torque noise in current perpendicular to the plane spin-valves by addition of Dy cap layers

{\text{Co}}_{50}{\text{Fe}}_{50}

High-output current-perpendicular to the plane giant magnetoresistance sensor with synthetic-ferrimagnet free layer and enhanced spin-torque critical currents

nanomagnet fixed layer and compare our experimental results to predictions of an analytical theory of a single-mode STNO dynamics [Tiberkevich et al., Phys. Rev. B 78, 092401 (2008)]. We find that a complete set of the oscillator spectral properties\char22{}power, frequency, spectral linewidth, and line shape as functions of current\char22{}is self-consistently described by the analytical theory for moderate amplitudes of oscillations

Ultrathin CoPt-pinned current perpendicular to the plane spin valves

(\ensuremath{\lesssim}70\ifmmode^\circ\else\textdegree\fi{})

Time- and vector-resolved magneto-optical Kerr effect measurements of large angle precessional reorientation in a 2×2μm2 ferromagnet

of the free-layer magnetization.

Zero field high frequency oscillations in dual free layer spin torque oscillators

The magnetotransport properties of current perpendicular to the plane giant magnetoresistive spin-valves utilizing (CoFe)100−xGex alloys are investigated. The composition range of 21≤x≤32 at. % is determined to be the alloy composition that maximizes magnetoresistance. ΔRA values of 2.6 mΩ–μm2 are measured for spin-valves with CoFeGe in the free and reference layer resulting in magnetoresistance values of greater than 6%, which is almost twice the value of similar spin-valves with CoFeAl alloys. An analysis of the physical properties of the CoFeGe thin films in the range of interest is also presented.