Observation and analysis of magnetic domain wall oscillations in Ga:YIG films

Abstract

We report the observation of damped oscillations of a single straight magnetic domain wall stabilized by an externally applied field gradient in a Ga-YIG film (Y2.9La0.1Fe3.8Ga1.2O12). The measurements are performed at various field gradients, in-plane fields, and wall drive fields. We analyzed the results using the Landau-Lifshitz-Slonczewski (LLS) theory and obtained the wall width parameter Δ≡ (A/Ku)1/2 = (0.89±0.15) ×10−5 cm and the corresponding wall mass m0≡ (2πγ2Δ)−1= (5.2±0.9) ×10−11 g cm−2, where A is the exchange constant, Ku is the uniaxial anisotropy constant, and γ is the gyromagnetic ratio of the material; the Gilbert damping constant α=0.005±0.001; and the reduced Landau-Lifshitz damping constant λ/γ2= (1.3±0.3) ×10−9 Oe2 s. The wall mass according to Döring as calculated from γ, A, and Ku is m0=[2πγ2(A/Ku)1/2]−1= (8.1±0.6) ×10−11 g cm−2 and is higher than the experimental value. The observed oscillations allowed an independent determination of the magnetization of the material (4.2±0.8 G) in agreement with a direct measurement (4.8±0.5 G). In an applied in-plane field of 262 Oe the peak velocity was 530 m s−1. This value is lower by a factor of 1.6 compared to the peak velocity predicted from the LLS theory. From an observed asymmetry in the dependence of the wall oscillation frequency on the applied in-plane field we deduced that at the domain wall an effective in-plane field of 23±6 Oe is present, which is in the direction of the stray field at the film-air interface. A model of a film having two layers is proposed to explain this field. At a low in-plane field we observed a wall oscillation with a low frequency, depending on the drive field amplitude. It is not excluded that this slow oscillation is due to a wall containing Bloch lines.