Muons and magnets

Abstract:

Using a transfer matrix method, the band structure is calculated for a spin-dependent generalization of the Kronig-Penney model which consists of a one-dimensional array of delta function potentials whose strengths depend on the relative orientation of the electron spin and a vector located at each delta function site, the direction of which is helically modulated. This is compared with a spin-independent Kronig-Penney model in which only the amplitude of each delta function is modulated. The period of the modulation can be incommensurate with the periodicity of the delta function array. The fractal nature of the band structure in the spin-independent case is shown to be quenched by the additional symmetry in the spin-dependent model.

Abstract:

A novel combination of electron- and ion-beam lithography has been used to prepare Fe gratings with wire widths of 0.5 μm and wire separations in the range 0.5-4 μm from an Fe/GaAs (001) film of thickness 25 nm. With an in-plane magnetic field applied perpendicular to the length of the wires, a harder magnetisation loop is observed using the magneto-optic Kerr effect (MOKE), compared with that observed in the unprocessed film. We observe a strong effect in the magnetoresistance (MR) when the magnetic field is applied transverse to the wires. It is believed that this effect originates from the highly non-uniform demagnetising field in each wire of the grating. These results demonstrate that the combination of MOKE and MR measurements can provide important information about the magnetisation reversal processes in magnetic gratings and can be used to understand the effect of shape anisotropy on magnetic properties. © 1994.

Abstract:

We report the observation of a magnetic transition at around 90 mK in the nitronyl nitroxide radical system para-pyridyl nitronyl nitroxide (p-PYNN) in zero applied field using the muon-spin rotation (μSR) technique. © 1994.