Abstract:
High spin-polarization in a magnetic material is essential for excellent performance of future spintronic devices and in that regard, half-metallic materials are promising candidates when incorporated into magnetoresistive devices such as magnetic tunnel junctions (MTJs) for spin transfer torque magnetic random access memory (STT-MRAM). As there is an increasing thrust toward device miniaturization and achieving faster switching times, it is likely that magnetic recording materials will be operating at higher frequencies and hence understanding the interplay between the magnetic anisotropy and the magnetization reversal process is of crucial importance both from technological and fundamental perspectives. Broadband ferromagnetic resonance (FMR) spectroscopy is an excellent tool to probe the dynamic magnetic properties of these half-metallic materials. Our investigation suggests that these low damping materials exhibit ‘anisotropic magnetization relaxation’ due to misfit dislocation (in case of Heusler CoxFe3-xSi thin films) as well as the presence of ‘magnetostatic spin waves’ due to the long-range dipolar interaction (in case of rutile CrO2 thin films). Furthermore, vector magneto-optic Kerr effect (MOKE) magnetometry reveals that single crystal CrO2 thin films are magneto-optically anisotropic with two different refractive indices. The structural anisotropy of the tetragonal CrO2 induces the magneto-optical anisotropy. On the other hand, changing the stoichiometry in epitaxial CoxFe3-xSi thin films results in the co-existence of the uniaxial magnetic anisotropy and the cubic magnetic anisotropy. The magnetization reversal processes are associated with the one-jump and two-jump reversal steps that depend critically on the competition between the uniaxial and cubic anisotropies present in these samples.
