Tailoring Curie temperature and magnetic anisotropy in ultrathin Pt/Co/Pt films

The dependence of perpendicular magnetization and Curie temperature (T-c) of Pt/Co/Pt thin films on the thicknesses of Pt seed (Pt-s) and presence of Ta buffer layer has been investigated in this work. Pt and Co thicknesses were varied between 2 to 8 nm and 0.35 to 1.31 nm (across the spin reorientation transition thickness) respectively and the T-c was measured using SQUID magnetometer. We have observed a systematic dependence of T-c on the thickness of Pt-s. For 8nm thickness of Pt-s the Co layer of 0.35nm showed ferromagnetism with perpendicular anisotropy at room temperature. As the thickness of the Pt-s was decreased to 2nm, the T-c went down below 250K. XRD data indicated polycrystalline growth of Pt-s on SiO2. On the contrary Ta buffer layer promoted the growth of Pt(111). As a consequence Ta(5nm)/Pt(3nm)/Co(0.35nm)/Pt(2nm) had much higher T-c (above 300K) with perpendicular anisotropy when compared to the same stack without the Ta layer. Thus we could tune the ferromagnetic T-c and anisotropy by varying the Pt-s thickness and also by introducing Ta buffer layer. We attribute these observations to the micro-structural evolution of Pt-s layer which hosts the Co layer. (C) 2016 Author(s).