Magnetic properties of TM/RE bilayer thin films

I. Zoto University of Alabama

The magnetic recording technology badly needs higher magnetization materials in order to write high anisotropy media which is required for thermal stability at small bit sizes. It is conceivable that transition metal-rare earth bilayers and trilayers might allow magnetizations higher than that available from transition metal alloys if the strong exchange interactions of the transition metal layer could raise the Curie temperature of an adjacent, high moment rare earth layer. Here we report the magnetic and structural properties of bilayers thin films prepared by magnetron sputtering. The magnetic and structural properties are studied by low temperature Vibrating Sample Magnetometry, Polarized Neutron Reflectivity, X-Ray Diffraction, and X-Ray Reflectivity. A Stoner-Wohlfarth model is also applied to simulate the hysteresis loops. We find that Ni and Gd have a negative interfacial exchange interaction, so the magnetizations align antiferromagnetically at zero applied fields. Simulation results are in good agreement with the experimental data and confirm the antiferromagnetic coupling. Polarized neutron reflectivity confirms the antiferromagnetic coupling in the remanent state and indicates that the magnetic moments of Gd and Ni align parallel to the field as the applied field is increased to 0.79 T.

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