2018 Volume 42 Issue 5 Pages 102-109
Effects of MgO cap-layer and substrate on L10-ordered FePt film structure are investigated by high-resolution transmission electron microscopy (TEM) for FePt thin films prepared on (001) oriented substrates by using a two-step method consisting of low temperature (200 °C) film formation followed by high temperature (600 °C) annealing. The TEM observation has shown that the crystal lattice of A1-FePt film (10 nm thickness) on MgO(001) substrate with 2-nm-thick MgO cap-layer is strained in the lateral direction to substrate surface, and by annealing the film structure varies to L10-ordered phase consisting of L10(001) variant with the c-axis aligned perpendicular. The FePt film in a sample of L10-FePt(2 nm)/VN(001) is consisting of L10-(001) variant, whereas the FePt film in a L10-FePt(2-nm average thickness)/MgO(001) sample includes variants of L10(100),(010) with the c-axis lying in-plane in addition to L10(001) variant. The lattice mismatch with substrate material is decreased by introduction of misfit dislocation and by lattice bending in L10-FePt crystal. The variant structures are interpreted to be influenced by the lattice strain in A1-FePt film during the L10-crystal nucleation stage at the high temperature annealing process. Based on the experimental results, a model to explain the phase transformation from disordered A1 to ordered L10 involving nucleation and growth of L10-crystal is proposed.
