Structure and magnetic properties of ultrathin Ni films on Pt(111) with Co buffer layers

The growth mode and the structure of ultrathin Ni films on Pt(111) with Co buffer layers were studied by low-energy electron diffraction (LEED) and Auger electron spectroscopy. The comparative study of the magnetic properties between Ni/Pt(111) and Ni/1 ML Co/Pt(111) was investigated by magneto-optical Kerr effect. The oscillation of the specular beam of LEED and the Auger uptake curve were used to calibrate the thickness of Ni overlayers and to study the growth mode of Ni thin films on 1 ML Co/Pt(111). The study of the alloy formation for Ni/1 ML Co/Pt(111) showed that the temperature for mixing Ni and Co in the upper interface without diffusing into the bulk of Pt is independent of the thickness of Ni overlayers. By further increasing the temperature, Co and Ni diffuse into Pt bulk simultaneously to form Co-Pt, Ni-Pt, and Ni-Co-Pt alloys. The temperature of the formation of these alloys is dependent on the Ni thickness. Studies of the magnetic properties showed that the easy axis of the magnetization changed from the cant to the out-of-plane direction when the Co buffer layer was inserted on Ni/Pt(111). The alloy formation causes some interesting changes in the polar Kerr signal. The enhancement in the out-of-plane magnetization of Ni/Co/Pt(111) is mainly contributed by the formation of Co-Pt alloy.