Bloch Wall Motion in Ferromagnetic Films Excited by Fast-Rising Hard-Axis Pulses

Abstract

Bloch wall motion along the hard direction of Permalloy films due to fast‐rising hard‐axis pulses is studied. Experimentally, it is found that for a given value of ḣ_⊥, the time rate of change of the applied field, wall motion occurs only for fields in excess of a certain minimum or threshold value h_th. Two distinct regions exist in this characteristic threshold curve. When ḣ_⊥ is large h_th is constant and when ḣ_⊥ is small h_th is a linear function of ḣ_⊥. Above h_th the wall displacement or movement per pulse increases linearly with driving field until this field approaches the value where the effect of Néel lines becomes important. A theoretical model taking account of both Bloch‐Néel wall transitions and the gyromagnetic effect of the spins in the walls and in the surrounding domains is proposed to account for the experimental results. The calculation assumes a reasonable wall structure and that Bloch walls are allowed to move freely except for a coercive force, i.e., a possibly more complicated interaction between the Bloch walls and Néel lines is neglected. With appropriate values of the constants and film parameters, the computation gives very good agreement with experimental results.