Spin Waves and Transport Properties in Ferromagnetic Co-Al-O and Fe-Al-O Granular Films : A Brillouin Scattering Study(Condensed matter: electronic structure and electrical, magnetic, and optical properties)

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A systematic Brillouin light scattering (BLS) study on long-wavelength spin waves (SWs) in ferromagnetic TM-Al-O (TM=Co, Fe) nano-granular films with thickness of >1μm was performed under magnetic fields of up to 4kOe at room temperature. BLS spectra consist of a pair of bulk SW peaks on both frequency sides and a surface localized SW peak only on the positive frequency side in this study. These SW frequencies as a function of the magnetic field can be fully reproduced by the magnetostatic frequency formula developed for a semi-infinite uniform ferromagnetic medium with an exchange coupling and an in-plane uniaxial magnetic anisotropy. We determined a set of the magnetic constants including the exchange field H_E for each film. Combining the exchange field H_E with the electrical resistivity p for each film at room temperature, we found an inverse-square law given by ρ=a(H_E)^<-2> for both the Co and Fe granular films with a_<Fe>=30.3μΩ.cm.(kOe)_^2 and a_<Co>=22.1μΩ.cm.(kOe)^2 respectively.
2008-09-15