Moving domain walls in ferromagnetic films with parallel anisotropy

Abstract

The dependence of wall mass and energy on wall velocity in thin Permalloy films is calculated by generalizing the Ritz model of Jakubovics (1978) for two-dimensional Bloch walls. In films 1000 Å thick, at low velocities, the wall mass is found to be about 52 times the value expected in bulk Permalloy. The mass increases with increasing velocity, v. Up to v≃3 × 10⁴cm s⁻¹ the increase is similar to that of a relativistic mass, namely proportional to (1−v ²/v _∞ ²)^−½, with a critical velocity v _∞ ≈ 14.6 × 10⁴ cm s ⁻¹ . For v 3 × 10⁴ cm s⁻¹ the increase of mass with velocity becomes more rapid. The model breaks down for velocities above ≃ 6 × lO⁴cm s⁻¹.