Magnetization Creep of Cross-Tie Walls

Abstract

Cross‐tie walls are known to have lower creep thresholds than non‐cross‐tie walls. This indicates that a special creep mechanism exists for cross‐tie walls but does not for non‐cross‐tie walls. Such a mechanism is described: In the presence of a pure dc easy‐axis field the magnetization antiparallel to the field buckles more, while the magnetization on the other side of the wall buckles less. This causes magnetostatic charges on the wall which cause the main wall itself to buckle in a zig‐zag fashion with bends at the Bloch lines between the cross‐ties and at the Bloch lines in the cross‐ties. When a hard‐axis field is applied, the Bloch lines between the (fixed) cross‐ties move along the wall, a situation resulting in magnetostatic charges causing the apex of the zig‐zags to move along with the Bloch lines. This distorts the symmetrical zig‐zags into asymmetrical ones having alternately long and short legs. At this point, each segment of the zig‐zag lies at a different angle from the easy axis than it did before the hard‐axis field was applied. When the hard‐axis field is relaxed, the zig‐zags become symmetrical again, and if a hard‐axis field of opposite polarity is applied, the zig‐zags lean the other way, i.e., the short segments become long and vice versa. This forces each segment to move with each hard‐axis pulse. Electron micrographs are presented which show all these processes clearly, and magnetostatic calculations of the stray field are made for each step of a typical case.