Non-uniform magnetisation and the vibrating-sample magnetometer

A general treatment is given of the response of vibrating-sample magnetometer pick-up coils to non-uniformly magnetised specimens. It is shown that the nth term in a multiple expansion of the sample magnetisation gives rise to a component of the induced EMF at the oscillation frequency, proportional to the (n+1)th derivative of the 'pick-up field', h, along the direction of the sample motion (h is the field such that h.m is the flux produced in the coils by a magnetic moment m). The analysis has been tested by observations of the signals produced by systems of small coils carrying a DC current. To illustrate the method, experiments on the remanent states of several ordered magnetic materials are described. Application of the method, using a SQUID magnetometer, to the possible measurement of the sublattice magnetisation of antiferromagnetic materials is described.