Orthogonal thin film magnetometer using the anisotropic magnetoresistance effect

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 H
m
, more than 50% will rotate in a sense determined by H
m
and a net magnetization M
m
will be present as the drive field goes through zero. H
m
is measured by detecting M
m
. In prevlous proposals M
m
is 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
^-5
V m/A sensitivity and 0.01A/m resolution have been obtained.