Larmor precession of polarised neutrons as a probe of the magnetisation of ultrathin epitaxial films

The authors demonstrate that a large and readily measurable rotation of the spin orientation occurs for polarised neutrons critically reflected from epitaxial ferromagnetic films. For a monolayer thickness BCC Fe film, a spin polarisation of approximately 5% is induced in the direction normal to the incident polarisation vector at the critical reflection condition. For buried films this polarisation change is found to be reduced only slightly. By measuring the polarisation rotation of the reflected beam in the critical reflection region, the absolute value of the magnetic moment per atom in the epitaxial film can be inferred with an accuracy which compares favourably with that which can be obtained using conventional polarised neutron reflection techniques.