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 (Y_2.9La_0.1Fe_3.8Ga_1.2O₁₂). 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/K_u)^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, K_u 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 K_u is m₀=[2πγ²(A/K_u)^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.