Domain wall effects in neutron depolarisation in Co-Cr films

A long-standing question connected with the magnetisation reversal mechanism in Co-Cr film is whether the film is to be considered as a continuous magnetic medium or as a medium composed of crystallites with parallel c-axes behaving magnetically as a collection of particles. A possibility to shed light on this question is to investigate the thickness of the domain walls (DWs). In a continuous medium the DWs would be Bloch walls of thickness of the order ~ ~ (A being the exchange constant and K u the constant of uniaxial anisotropy). In a particulate medium the DWs could (partly) coincide with crystallite boundaries. Exchange would play a minor role in determination of the thickness of the boundary, and hence it should be much thinner than a Bloch wall. On the other hand, by Cr segregation the boundary could be degenerated into a non-magnetic region of any thickness. In this paper the consequences of both views for static neutron depolarisation are discussed and compared with observations. length and A is the neutron wavelength in meters. For a domain model as shown in the cross section through the film in fig. 1, the depolarisation as a function of O is given by [1]: