Field dependence of strain imaging in magnetic observation of ferrite head

When a magnetic material was subjected to an external magnetic field, a strain was generated in the material and the strain was detected and imaged with a scanning probe microscope. The images obtained with unipolar fields, however, were quite different from those obtained with bipolar fields. We discuss the magnetic field dependence of magnetic strain imaging and propose a physical interpretation. We conclude that strains are magnetostrictive in weak fields, and are mainly caused by magnetic forces in strong fields. The images obtained with unipolar fields represent domain structures at the peak fields, and those with bipolar fields represent the distribution of asymmetry of magnetization reversal.