Theory of surface states in spin wave resonance

Fe–Al alloys containing 30 to 50 at. % Al were investigated by Mossbauer spectroscopy. Both ordered alloys, having the CsCl or B2 structure, and alloys severely cold‐worked by crushing were studied. At room temperature, all of the ordered alloys exhibit only paramagnetic lines, whereas the crushed alloys exhibit both paramagnetic and ferromagnetic lines, the intensity of the former increasing from 0% to 100% as the Al concentration increased from 30% to 50%. The results can be explained by considering the nearest neighbor configurations of Fe atoms in the ordered and deformed alloys, with slight corrections for next‐nearest neighbors. Plastic deformation induces ferromagnetism by creating large numbers of antiphase boundaries across which the number of Fe–Fe nearest‐neighbor bonds is significantly greater than in the ordered alloy. The observed percentages of paramagnetic and ferromagnetic material and the average effective field values in the crushed alloys indicate that the average linear dimensions of the antiphase domains are about six atomic distances. In addition, the effects of antiphase boundaries and short‐range order produced by heat treatment have been observed in alloys of the DO3 structure (BiF3 type) having less than 25% Al.

Mössbauer Studies of Ordered and Cold‐Worked Fe–Al Alloys Containing 30 to 50 at. % Aluminum

Spin‐wave resonance at 10 GHz has been observed in thin (? 5 μm) garnet films of approximate composition Y2.85La0.15Fe3.75Ga1.25O12. The films were grown by LPE on [111]‐oriented gadolinium gallium garnet substrates, both from a nonstirred melt (vertical mode of dipping) and a stirred melt (horizontal dipping, applying axial substrate rotation). The spectra exhibit large numbers of strongly excited modes with large deviations from quadratic spacing, which are interpreted in terms of a volume inhomogeneity of the uniaxial anisotropy constant Ku. Two models are used to explain the experimental spectra. In one model the film is considered as being built up of exchange coupled layers having different uniaxial anisotropy constants Ku. In the second model it is assumed that Ku varies linearly with the distance from the substrate, but with different slopes in different regions. No pinning is assumed at the surfaces. A simple graphical method is presented for determining the normal modes of films with these types...

Spin‐wave resonance spectra of inhomogeneous bubble garnet films

We report ferromagnetic resonance experiments on Ga1−xMnxAs thin films. For the dc magnetic field perpendicular to the sample plane, we observe up to eight distinct resonances, which we attribute to spin wave modes. To account for the spacing of the resonances, we infer a linear gradient in the magnetic properties, which is ascribed to a linear variation of the uniaxial magnetic anisotropy with film thickness. Values of D=(1±0.4)×10−9 Oe cm2 for the spin stiffness and JMnMn≈1 meV for the exchange integral between Mn spins are obtained.

Spin wave resonance in Ga1−xMnxAs

The half-metallic half-Heusler alloy NiMnSb is a promising candidate for applications in spintronic devices due to its low magnetic damping and its rich anisotropies. Here we use ferromagnetic reso ...

A. M. Portis

Papers

Low‐lying spin wave modes in ferromagnetic films