Tailoring Spin Relaxation in Thin Films by Tuning Extrinsic Relaxation Channels
The importance of extrinsic spin relaxation processes such as magnon-magnon scattering for the overall damping in ferromagnetic thin films has been shown for low relaxation rate systems. Due to its anisotropic behavior, it offers an opportunity for controlling and tailoring the spin relaxation. In this paper, a ferromagnetic resonance study of a system with pure Gilbert damping Fe94.5Si5.5/MgO(001) is shown. Fe3Si/MgO(001) systems with native magnon-magnon scattering are discussed. Possibilities for inducing magnon-magnon scattering by volume and surface defects in these systems are presented, offering a method for controlled tailoring of the overall damping in thin films.
Magnetocrystalline anisotropy and Gilbert damping in iron-rich Fe1−xSix thin films
The magnetocrystalline anisotropy of Fe1−xSix (0≤x≤0.4) epitaxial thin films on MgO(001) was studied by ferromagnetic resonance. The experimental results are in good agreement with theoretical predictions of ab initio electronic structure calculations using the fully relativistic Korringa-Kohn-Rostoker Green's function method within spin-density-functional theory. The Gilbert damping α is found to be isotropic by theory and experiment with a minimum at the composition x=0.2.
VLA stereoscopy of solar active regions. 2: Altitude, relative motion, and center-to-limb darkening of 20 centimeter emission
A newly developed method of stereoscopic correlation is applied to solar radio maps at a wavelength of 20 cm. On the basis of stereoscopic correlations between radio maps obtained on 6 different days we establish the presence of 66 radio source components associated with 22 active regions. We find the following statistical results for active region source structures at 20 cm: 1. The observed lifetime is consistent with an exponential distribution having an e-folding time scale of greater than 18 days. 2. The average altitude of 20 cm sources is 25 +/- 15 Mm; 90% of the sources are found in heights less than 40 Mm. 3. The average diameter of discrete source structures is 48 +/- 15 Mm, implying a vertical/horizontal aspect ratio of q(sub A) approx. = 0.5. 4. No significant source motion has been found with respect to the standard differential rotation rate of Omega = 13.45 deg - ((3 deg (sin(exp 2)B)). 5. We find a statistical limb darkening, which can be described by the relation (T(sub B)(alpha))/T(sub B)(0)) = 0.4 + ((0.6(cos(exp 2) alpha)) for sources with T(sub B) greater than 0.5 MK. 6. The degree of source polarization is 15% +/- 10% and is independent of source location. 7. Bright sources (greater than or approximately equal to 0.5 MK), or equivalently, long-lived sources (greater than or approximately equal to 5 days) show a systematic variation of their altitude as function of the center-limb distance.