Effect of TiN-MgO intermediate layer on the microstructure and magnetic properties of FePt thin films

In order to achieve the application of FePt based films, great progresses have been made in the fabrication of granular FePt thin films using MgO or TiN underlayer/intermediate layers. However, the MgO intermediate layer possessing small surface energy led to large opening-up in the in-plane hysteresis loop while the TiN intermediate layer possessing large surface energy caused the formation of the semi-spherical FePt grains with big grain size and poor grain isolation. In order to solve these problems, we proposed a new intermediate layer- TiN-MgO. As compared with TiN intermediate layer, the TiN-MgO intermediate layer had smaller surface energy and larger interfacial energy, thus favoring Volmer-Weber type (island) growth of FePt. As seen from planar view TEM images (Fig.1a and b), by doping MgO into the TiN intermediate layer, the grain boundaries were more distinct. Moreover, grain size decreased from 8.77 nm to 7.58 nm for 50 vol.% MgO doping into TiN. The cross-sectional TEM images (Fig.1 c and d) indicated that FePt-SiN_x-C films were grown on the top of TiN-MgO polycrystalline intermediate layer with a single-layer structure and FePt grains were well isolated. Furthermore, the grain shape of FePt became more uniform with doping MgO into TiN intermediate layer. Although, the perpendicular anisotropy had a little deterioration which was due to the nonwetting of FePt grains on TiN-MgO intermediate layer (Fig.1 e), the 4nm-SiN_x 40 vol.%-C 20 vol.% film grown on TiN/TiN-MgO 50 vol.% with a larger out-of-plane coercivity of 21.7 kOe and a small in-plane coercivity of 3.5 kOe can still obtained (Fig.1g).