Coupled Oscillations of the Magnetic DomainDomain Wall System in Substituted Garnet Thin Films
Abstract
The dynamic response of parallel stripe domains in Ga substituted YIG thin films was studied using a rf spectrometer, incorporating an rf structure as the coupling device. Three signals, corresponding to the "inphase" ((omega)('+)) and "out of phase" ((omega)(')) domain ferromagnetic resonance and the domain wall resonance (DWR) are observed for the first time in the same frequencyfield regime. As an applied inplane field H(,P) is increased toward in plane saturation fields, the DWR and DR signals are observed to repel each other, resulting in frequency gaps. A series of five films, with 4(pi)M ranging from 4751275 G and H(,u) ranging from 825450 Oe and H(,sat) in the range 190690 Oe were examined. The frequency range studied was 102400 MHz for inplane fields up to 1 K Oe. A brief discussion of the samples, experimental set up and observations are given. A unified theory is developed to account for the dynamics of a system of magnetic domains and walls. A generalized expression for free energy is written down. The resulting equations of motion, in the linear response limit, are shown to yield a 6 x 6 determinant, whose zeros determine the frequencies of coupled oscillation and hence an expression for the observed frequency gaps. The effect of demagnetization energy is taken into account and the theory of Domain Wall Resonance for bubble materials is modified to include the effects of finite value of Q. Exact calculations are carried out for such parameters as wall energy, domain wall mass, etc. A new result of this work is the lifting of the singularity in the DWR frequency as saturation is approached. Effects of cubic anisotropy energy are also discussed. The theory is seen to fit the experimental data very well upon the introduction of two phenomenological fitting parameters, H(,1) and (alpha), especially in samples with Q > 1. The agreement between the theory and the experiment is discussed.
 Publication:

Ph.D. Thesis
 Pub Date:
 1985
 Bibcode:
 1985PhDT........64R
 Keywords:

 FERROMAGNETIC RESONANCE;
 RESONANCE;
 YIG;
 PARALLEL STRIPE;
 DEMAGNETIZING FACTOR;
 Physics: Condensed Matter