Wall oscillations in the presence of in-plane fields in magnetic bubble materials

Abstract

Wall oscillations after an abrupt change in bias field are observed in parallel-stripe domains as a function of both the magnitude and direction of an external in-plane field. Two distinctly different types of oscillations are found. For small values of in-plane field (Hip<10 Oe) nonlinear oscillations are observed. The wall velocity is saturated, resulting in oscillations with a characteristic triangular shape. The saturation velocity varies from 6.8 m/sec with Hip=0 to 12 m/sec with Hip=10 Oe. The half-period of the oscillations, τ/2, increases with increasing bias pulse amplitude Ha from τ/2=50 nsec with Ha=2.0 Oe, to τ/2=140 nsec with Ha=6.0 Oe. Increases in the angle β between the in-plane field and the domain walls cause increases in τ/2. For larger values of the in-plane field (Hip≳30 Oe) linear oscillations are observed, in which the wall velocity changes with the instantaneous drive field Hextz, resulting in sinusoidal oscillations. The frequency of the oscillations, ν, increases with increasing Hip, typically over the range 18<ν<35 MHz for 40<Hip<160 Oe. For a fixed value of Hip, ν decreases with increasing β typically over the range 23≳ν≳16 MHz for 0°<β<80°. The frequency is independent of Ha over the range investigated (2<Ha<6 Oe). In the transition region between linear and nonlinear oscillations (10<Hip<30 Oe) τ/2 gradually decreases and becomes less dependent on Ha. Linear wall oscillations are successfully modeled by assuming a one-dimensional dynamic wall structure. Through comparisons with experimental results, it is shown that (1) the instantaneous wall velocity ? obeys the classic mobility relationship ?=γΔ0Hextz/α; (2) the intrinsic wall mass density is given by the Döring mass, (2πγ2Δ0)−1; and (3) the losses associated with wall motion are consistent with the FMR loss parameter.