Effects of TiO2 volume fraction on the microstructure and magnetic properties of CoPt-TiO2 nanocomposite films

CoPt-TiO2 nanocomposite films were synthesized by rapid thermal annealing of CoPt/TiO2 multilayers. The effects of TiO2 volume fraction on the microstructure and magnetic properties of the nanocomposite films were studied. Results showed that the ordering and texture of the L10-CoPt particles did not change with TiO2 content up to 76 vol.% of TiO2. However, the volume of the L10-CoPt particles in the film decreased with an increase in TiO2 content. Increasing TiO2 content effectively reduced the coalescence of magnetic grains when TiO2 content was larger than 56 vol.%. Both the out-of-plane coercivity and remanence ratio of the film decreased slightly with TiO2 content, but the in-plane coercivity and remanence ratio of the film decreased firstly and then increased after TiO2 content was larger than 56 vol.%. The reduction in the coercivity of the film should be due to the reduction in the size of the L10-CoPt particles. The reduction in remanence ratio might be due to the weakening of the exchange coupling strength between the magnetic grains when TiO2 content was increased, as indicated by the MFM images.