Characterisation of micron scale piezomagnetic materials in devices

The authors have previously discussed the use of piezomagnetic materials in microelectromechanical systems. Optimum response, in terms of piezomagnetic properties, comes from control of the ferromagnetic domain structure. It is important that moment rotation dominates the magnetisation process, the magnetisation rotating coherently through 90°. It is important to assess the magnetisation distribution on length scales less than the device dimensions. The sample volumes involved preclude inductive methods, and so an optical method is to be preferred. Fine spot sizes allow a plot of magnetisation, M, against field, H, in a device almost point by point. The magneto-optic Kerr effect (MOKE) is the chosen route. We have applied the MOKE technique to some simple lithographically defined structures, and have shown the power of the technique in discriminating various magnetisation modes, and hence intrinsic domain structures. Using well focused light it is possible to interrogate magnetic films of very small lateral dimension, including films grown in the full device configuration. The effects of growth parameters, and device activation can therefore be directly assessed