Recent experiments on magnetic tunnelling devices based on magnetite film show an unexpectedly low tunnel magnetoresistance despite a high magnetic transition temperature and a high spin polarization of the conduction electrons. The explanation is given in two parts. The first reason for the reduction is the quantum mechanical coupling and relaxation of the conduction electron and core spin. This can reduce the tunnel magnetoresistance substantially. The second is the surface effects in which the magnetic spins at the surface are frustrated as a result of fewer nearest neighbours, surface reconstructions, anti-phase boundaries and the superparamagnetic behaviour. This explains the rapid fall of the magnetization and the tunnel magnetoresistance with temperature.
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Srinitiwarawong et al. (2001) studied this question.
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