Mobility and Loss Mechanisms for Domain Wall Motion in Thin Ferromagnetic Films

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Abstract
Domain‐wall mobility for Ni–Fe alloy films has been measured as a function of film thickness from 300 to 1650 Å. Between 300 and 800 Å, the mobility decreases with increasing film thickness, ranging from 8×103 cm/sec·Oe at 300 Å to 3×103 cm/sec·Oe at 800 Å. Between 900 and 1000 Å, the mobility increases rapidly with increasing film thickness to about 7×103 cm/sec·Oe. Above 1000 Å, the mobility increases slowly with film thickness. These mobility data have been compared with predictions based on intrinsic and eddy‐current loss mechanisms utilizing available static domain wall‐shape information. Predictions based on a 180° Bloch or Néel wall model in which the magnetization rotates linearly through the wall are in disagreement with the present data over the entire range of film thickness. For the 300–800 Å thickness range, predictions based on Lorentz microscopy wall‐shape measurements are in good agreement with the measured mobility values. The crosstie structure associated with Néel walls in this thickness range does not appear to affect the mobility. Bitter patterns indicate that the sharp increase in mobility between 900 and 1000 Å may be associated with a wall structure transition in this region. For thicker films, mobility predictions based on static Bloch wall‐shape calculations are an order of magnitude lower than the observed mobilities. Lorentz microscopy wall‐shape measurements for 1200‐Å films yield wall widths of about 3000 Å significantly wider than calculated Bloch wall widths. Predictions based on these measured widths are in good agreement with the data. Although the calculation includes both intrinsic and eddy‐current losses, intrinsic losses dominate for crosstie or Néel wall motion in the 300–800‐Å thickness range and for Bloch wall motion in the 1000–1600 Å thickness range.