Orthogonal thin film magnetometer using the anisotropic magnetoresistance effect

Abstract

In an orthogonal thin film magnetometer a driving field oriented in the plane of a permalloy film along its hard-axis, saturates this film periodically in positive and negative direction. On return from saturation and in absence of a magnetic field component along the easy-axis, the magnetization in 50% of the film will rotate clockwise and in the remaining 50% anticlockwise giving rise to domain formation. With an easy-axis field component Hm, more than 50% will rotate in a sense determined by Hmand a net magnetization Mmwill be present as the drive field goes through zero. Hmis measured by detecting Mm. In prevlous proposals Mmis detected inductively. We propose the application of the anisotropic magnetoresistance effect by measuring either the planar Hall voltage or the resistance of the film with the dc-current at respectively 0° or 45° to the easy-axis. Expressions for the sensitivity of both the inductive and the magnetoresistive detection methods are derived, showing that the magnetoresistive method behaves better under miniaturization. With a 1 cm square permalloy film, using phase-sensitive detection of the planar Hall voltage, synchronously with the third harmonic of the drive frequency, 3×10-5V m/A sensitivity and 0.01A/m resolution have been obtained