Anisotropic behaviour of magneto-electric coupling in multiferroic composites

The anisotropy of the direct magnetoelectric effect in textured nickel ferrite/lead zirconate titanate strain mediated bilayer composites has been studied. The magnetic layers of these samples have been crystallographically textured in planes of the form {100}, {110} and {111}.
In this study, it is shown that the optimum bias field and the maximum
magnetoelectric coupling signal can be controlled by changing the alignment of
the applied magnetic field with respect to the magnetocrystalline anisotropy
directions. It is also shown that the product of the optimum bias field and the
maximum magnetoelectric coupling signal are proportional to the theoretical
saturation magnetostriction.
The samples have been magnetically characterised using a recommissioned and
developed biaxial vibrating sample magnetometer, capable of detecting the
component of a sample’s magnetic moment in 2 perpendicular directions and
thus determining the net magnetic moment vector of the sample. Coupled with
sample rotation this allows insight into the magnetic anisotropy of the sample,
which has been compared with a micromagnetic model.
A specialist magnetoelectric coupling rig has also been developed to allow
application of DC and AC magnetic fields to a sample simultaneously.
As part of the magnetic anisotropy study, a modified torque magnetometry
method has been developed to enhance the identification of the anisotropy
directions in magnetically soft samples, as well as a method by which torque
magnetometry can be approximated using the in-field direction component of
magnetisation as measured using a standard vibrating sample magnetometer.