Contact Mode Scanning Hall Probe Microscopy

Abstract

Scanning Hall probe microscopy (SHPM) is an established method for monitoring localized magnetic fields at the surfaces of ferromagnetic materials and magnetic media, as well as vortices in superconductors. Magnetic imaging measurements are usually made using Hall sensors with integrated scanning tunneling microscope tips (STM-tips). Hall probes are fixed to piezoelectric tubes and lowered to the sample surface until a tunneling current is detected, when feedback circuitry takes over to maintain the probe-sample separation and prevent damage to the device. However, Hall probes with STM-tips have limitations that include measurements requiring conducting sample surfaces and complicated electronics to monitor the tunneling current. Hall probe microscopy could be made more robust and offer improved magnetic sensitivity and spatial resolution by making measurements with the Hall probe in actual contact with sample surfaces without the use of STM tips and piezoelectric actuators. Here, we describe the development of a contact mode SHPM system (CM-SHPM), where the Hall probe was attached to a flexible cantilever and the probe-sample separation monitored using a simple strain gauge integrated onto the cantilever. The CM-SHPM offers a simple and highly reliable means of magnetic imaging of nonconducting samples over large areas and wide temperature ranges.