Tunnel Magnetoresistance of CoFeAlSi-MgO Granular films

The tunnel magnetoresistance (TMR) effects of granular films employing CoFeAlSi (CFAS) were investigated. The granular films were composed of MgO buffer, CFAS, and protective MgO layers. A structural change from continuous to granular structures was clearly seen in the resistivity, depending on the nominal thickness of CFAS. The samples prepared on the heated substrate showed large MR ratios, with a maximum MR ratio of 5.5% for a CFAS thickness of 2.0 nm. From the X-ray photoelectron spectroscopy depth profile, Fe was preferentially oxidized on the surface of granules, although Co was not. TEM micrographs showed relatively uniform granules, with a diameter of 3.0-5.0 nm, for the samples prepared on a substrate heated at 200°C. However, an L21 ordered structure was not confirmed due to low substrate temperature.