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 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.

Near-surface nanoscale InAs Hall cross sensitivity to localized magnetic and electric fields.

We have measured the room temperature response of nanoscale semiconductor Hall crosses to local applied magnetic fields under various local electric gate conditions using scanning probe microscopy. Near-surface quantum wells of AlSb/InAs/AlSb, located just 5 nm from the heterostructure surface, allow very high sensitivity to localized electric and magnetic fields applied near the device surfaces. The Hall crosses have critical dimensions of 400 and 100 nm, while the mean free path of the carriers is about 160 nm; hence the devices nominally span the transition from diffusive to quasi-ballistic transport. With certain small gate voltages (V(g)) the devices of both sizes are strongly responsive to the local magnetic field at the center of the cross, and the results are well described using finite element modeling. At high V(g), the response to local magnetic fields is greatly distorted by strong electric fields applied near the cross corners. However we observe no change in behavior with the size of the device.