Question

Please: Answer all of below &Clear and briefly answer & Clearly identifiable handwriting or computer typing

Please give arguments about what determines the width of a ferromagnetic domain
wall?

Answer 1

‘Slow’ rotation of magnetic dipole across the wall occurs
as large energy cost in having neighbouring atoms with
different dipole orientation (exchange energy).
Within the domain wall, the majority of the magnetic
dipole moments may be pointing out of the easy direction.
This will then contribute to the anisotropy energy.

As domains get smaller, magnetostatic energy reduces,
however have more atoms found in the domain walls, and
so the anisotropy energy grows.
Resulting balance between anisotropy, exchange and
magnetostaic energies determine overall structure of
domains and leads to establishment of an equilibrium
structure.

Edges of domains are Called domain ‘walls’. Width of wall can be a few 100 atoms wide.The magnitude of the magnetism M of a sample,  is equal to the vector sum of the magnetisation of the domains The regions of spontaneous magnetisation obviously already exist and the external field H produces an overall magnetisation M by altering their distribution (size and distribution).