Abstract
The magnetic coupling between two permalloy layers with Cr separating layer was studied using longitude magneto-optical Kerr effect measurement (LMOKE), polarized neutron and X-ray diffraction XRD. The coupling between two permalloy layers is antiferromagnetic-like when the Cr thickness is near 2.4 nm along the easy axis. A strong biquadratic coupling term has been found from the polarized neutron reflectivity study. The strong biquadratic coupling may be caused by the rough interface between the permalloy and Cr layers. The coupling strength is getting stronger as lower temperature but higher than a phase change temperature TN. As the temperature is lower than TN, the coupling strength drops sharply. It's believed that the TN is short-range antiferromagnetic order and long-range antiferromagnetic order of the type of an incommensurate spin density wave transition. The missing GMR effect of this system might be due to this strong biquadratic coupling of the permalloy layers. X-ray diffraction, X-ray anomalous scattering and X-ray absorption near edge spectroscopy are used to study the structure of epitaxial films. The hysterisis loop with two-fold symmetry was discussed with the crystal structure. Usual X-ray diffraction was hard to determine the structure of Cr because the film was so thin. The anomalous X-ray diffraction and reflectivity is helpful to analyze the structure and interface roughness of Cr layer with permalloy neighbors. X-ray absorption near edge spectroscopy was also done to study the Cr structure. As the Cr layer is thinner, the absorption spectrum of Cr is more fcc-like as permalloy. On the opposite, as the Cr layer is thicker, the spectrum of Cr is more similar to bcc bulk Cr. The results imply that the Cr layer with permalloy neighbors could have slight of interdiffusion. Another possibility is the thin Cr layer could be strained by permalloy neighbors and formed psudomorphic fcc structure.