Ferromagnetic Resonance Spectroscopy Studies of Permalloy/Copper/Chromium/Copper thin films

A theroretical and experimental study of 10Py/10Cu, 10Py/10Cu/xCr/10Cu (with x=4,7, 10,13 nm) thin films has been performed. The thin films were fabricated by the sputter deposition technique at NTNU Nanolab and afterwards a FMR-experiment were performed on them at the temperatures 180K, 210K, 240K, 280K, 330K and 360K. The anisotropy field, exchange bias and offset field were extracted and analysed. The results revealed vastly higher magnitude of anisotropy field and exchange bias for the 4 Cr film, compared to the other samples. Under 300K, the anisotropy field of 4Cr is ~60 Oe which is about 30 times larger than anisotropy field of the other samples. The exchange bias for 4Cr is ~8 Oe, which is about 10 times larger than the exchange bias of the other samples. The significant difference in exchange bias is explained by the spin-density wave amplitude, which increases for decreasing Cr-thicknesses. However, this model does not predict the large drop-off to the 7 Cr, 10 Cr and 13 Cr samples. The measurement of PyCu revealed an exchange bias of the same order as the 7-13 Cr samples, indicating that the exchange coupling between the Py and Cr layer is very weak, since it is of the same magnitude as the PyCu film. A theoretical description of H_Res and Delta H of the system was given, but not fulfilled. Factors, mainly due to spin pumping and interface effects must be identified and adapted to the equations