Large lattice mismatch effects on the epitaxial growth and magnetic properties of FePt films

Heteroepitaxial film growth is crucial for magnetic and electronic devices. In this work, we reported the effects of the large lattice mismatch and film thickness on the epitaxial growth and magnetic properties of FePt films on ZrxTi1−xN (0 0 1) intermediate layer. FePt films with different thickness were deposited on ZrTiN intermediate layers with various doping concentration of TiN in ZrN. The increase in doping concentration of TiN caused a decrease in the lattice parameters of ZrTiN intermediate layer. It was found that (0 0 1) epitaxy of FePt 10 nm films was only achieved on ZrTiN intermediate layer when the TiN composition was ≥25 vol%, while (0 0 1) texture of 5 nm films was achieved on ZrTiN intermediate layer with a minimum of 50 vol% TiN composition. The in-plane lattice constants of FePt and Zr0.70Ti0.30N (25 vol% TiN) were 3.870 Å and 4.476 Å, respectively, which resulted in a lattice mismatch as large as 15.7%. These large lattice mismatch heterostructures adopted 7/6 domain matching epitaxy. The magneto-crystalline anisotropy of FePt films was improved with the increase in lattice mismatch. Intrinsic magnetic properties were extrapolated for FePt (30 nm)/Zr0.70Ti0.30N (30 nm)/TaN (30 nm)/MgO, and the Ms(0 K) and K1(0 K) were 1042 emu/cc and 5.10 × 107 erg/cc, respectively, which is comparable to that of bulk L10 FePt.