Nanoscale magnetic field detection using a spin torque oscillator

Abstract

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 sensor's 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.

Micromagnetic simulations of magnetization dynamics in a nanowire induced by a spin-polarized current injected via a point contact

“…Up to date, two major STNO geometries have been studied: (i) spin valve nanopillars in which propagation of magnetic excitations is restricted by the ferromagnet boundaries in all three spatial dimensions (zero-dimensional systems, 0D) 5,27,28 and (ii) point contacts to spin valves in which magnetic excitations can propagate in the plane of the spin valve (twodimensional systems, 2D) 6,8,11,12,29 . The two-dimensional systems offer the advantage of phase locking of nearby STNOs via interaction by spin waves propagating in the common ferromagnetic free layer 11,12 .…”

Frequency-based nanoparticle sensing over large field ranges using the ferromagnetic resonances of a magnetic nanodisc

“…By electrically detecting these resonances, nanoparticle-induced modifications to the resonances can be exploited to create nano-scale, frequency-based nanoparticle detectors for applications such as solid-state bio-detection 28 . Due to the non-uniform spatial profiles of resonant mode dynamics, the observed shifts (exceeding 300 MHz in some cases) can depend strongly on the position of the nanoparticle.…”

Scaling effect of spin-torque nano-oscillators

“…The magnetization vector trajectories reveal that irregular oscillations exist in smaller devices. Our findings suggest that a 20 × 20 nm 2 The areal density of commercial hard disk drives (HDD) is increasing rapidly, which requires the development of new HDD read sensor. For nanoscale magnetic recording sensing, a novel spintorque oscillator (STO)-based read head sensor has been proposed as a promising candidate.…”

“…For nanoscale magnetic recording sensing, a novel spintorque oscillator (STO)-based read head sensor has been proposed as a promising candidate. [1][2][3] When a spin-polarized current is injected into a magnetic layer, depending on the direction and intensity of the charge, the local magnetization is switched to the opposite direction or is driven into a permanent precession along the effective field. The precession frequency is tunable by the external magnetic field or applied current.…”

“…When the STO dimension is shrunk to less than 30 nm, the linewidth is estimated to be around 200 MHz. 2 Micromagnetic simulations demonstrated that, for STOs smaller than 40 nm, reducing the device size lowers the oscillation-onset voltage. Furthermore, the stable oscillation region of the free layer is reduced due to the expansion of the unstable oscillation region of the reference layer in the oscillation phase diagram.…”