Temperature Dependence of the Interlayer Exchange Interaction in Co/Pd/Co Magnetic Heterophase Material

A direct experimental study of the temperature dependence of the field HJ proportional to the energy of the interlayer exchange interaction J is carried out in heterophase samples with perpendicular magnetic anisotropy consisting of ferromagnetic Co layers separated by a nonmagnetic Pd interlayer. Using Kerr microscopy, the fields of domain nucleation HN in samples magnetized to saturation and the fields of interlayer exchange interaction are measured at different thicknesses of the nonmagnetic interlayer in the temperature range from 15 to 300 K. It is shown that the nucleation field in both ferromagnetic layers decreases steadily with increasing temperature. The threshold temperatures Ti are found to be dependent on the thickness of Pd. At T < Ti, domains of the new phase are generated simultaneously in both layers. At T > Ti, the nucleation of domains in layers occurs in different fields and regions of the samples. In the specified temperature range, field dependences of the velocity of the domain boundaries v(H) in one of the layers are obtained with the other layer uniformly magnetized. It is established that the fields for the v(H) dependence differ by 2HJ when the boundaries move in opposite directions (with magnetic-field strengths of +H and –H). As the temperature decreases, the value of this field increases. This increase is greater in samples with a thinner interlayer, which is consistent with the theoretical dependences obtained earlier. However, a number of important unpredicted features of the behavior of the domain structure with changes in temperature are revealed. It is shown for the first time that at low temperatures the value of HJ is proportional to T–1.