Preparation of high moment CoFe films with controlled grain size and coercivity

In this paper a preparation method for high moment CoFe thin films with soft magnetic properties is reported. A full control of coercivity in a series of 20-nm-thick CoFe films has been achieved without using seed layers, additives, or thermal annealing. The films were sputtered directly onto Si substrates and the coercivity was varied by changing the mean grain size in the sputtered films. The mean grain size was in turn controlled via the sputtering rate. A reduction in the coercivity has been observed from 120Oe for samples with a mean grain size larger than 17nm down to 12Oe for a sample with a mean grain size of 7.2nm. The results are in good agreement with the “random anisotropy model” relating the coercivity to the mean grain size in polycrystalline ferromagnetic films.