The activated torsion oscillation magnetometer

TL;DR

The paper introduces the activated torsion oscillation magnetometer (ATOM), a sensitive device using cantilever resonance to measure magnetic properties with high precision across a wide temperature range.

Contribution

It presents a detailed model of cantilever dynamics, a novel capacitance detection method, and the design of a prototype magnetometer with reduced noise and parasitic effects.

Findings

Detection sensitivity of about 0.5×10^-11 Am^2

Capacitance detector can detect displacements of 0.1 nm

Operates effectively from 4.2 K to 300 K

Abstract

The activated torsion oscillation magnetometer exploits the mechanical resonance of a cantilever beam, driven by the torque exerted on the sample by an ac field applied perpendicularly to the film plane. We describe a model for the cantilever dynamics which leads to the calculation of the cantilever dynamic profile and allows the mechanical sensitivity of the instrument to be expressed in terms of the minimum electronically detectable displacement. We have developed a capacitance detector of small oscillations which is able to detect displacements of the order of 0.1 nm. We show that sensitivities of the order of 0.5(10-11 Am2 can be in principle achieved. We will subsequently describe the main features of the ATOM prototype which we have built and tested, with particular attention to the design solutions which have been adopted in order to reduce the effects of parasitic vibrations due either to acoustic noise, originating from the ac field coil, or to eddy currents in the capacitor electrodes. The instrument is mounted in a continuous flow cryostat and can work in the 4.2-300 K temperature range. Finally, we will show that our experimental set-up has a second mode of operation, named Torsion Induction Magnetometer (TIM).