Magnetometry of micro-magnets with electrostatically defined Hall bars

TL;DR

This paper demonstrates a method to enhance the sensitivity of electrostatically defined Hall bars for micro-magnetometry, enabling detailed characterization of sub-micrometer ferromagnets and their stray fields at low temperatures.

Contribution

It introduces a technique to restore Hall bar sensitivity at low temperatures using high current density, allowing measurement of smaller micro-magnets beyond conventional size limits.

Findings

Sensitivity nearly restored at low temperatures with high current density

Able to measure magnetization curves of 440 nm wide micro-magnets

Direct measurement of stray magnetic field inhomogeneity

Abstract

Micro-magnets are key components for quantum information processing with individual spins, enabling arbitrary rotations and addressability. In this work, characterization of sub-micrometer sized CoFe ferromagnets is performed with Hall bars electrostatically defined in a two-dimensional electron gas. Due to the ballistic nature of electron transport in the cross junction of the Hall bar, anomalies such as the quenched Hall effect appear near zero external magnetic field, thus hindering the sensitivity of the magnetometer to small magnetic fields. However, it is shown that the sensitivity of the diffusive limit can be almost completely restored at low temperatures using a large current density in the Hall bar of about 10 A/m. Overcoming the size limitation of conventional etched Hall bars with electrostatic gating enables the measurement of magnetization curves of 440 nm wide micro-magnets with a signal-to-noise ratio above 10^3. Furthermore, the inhomogeneity of the stray magnetic field created by the micro-magnets is directly measured using the gate-voltage-dependent width of the sensitive area of the Hall bar.