Comparative study in magnetic properties of Ni/Co/Pt(111) and Co/Ni/Pt(111)

Magneto-optical Kerr effect (MOKE), low-energy electron diffraction (LEED), and Auger electron spectroscopy (AES) were used to study the magnetic properties and the growth modes of thin Ni films on 1ML Co/Pt(l 11) and Co/1 ML Ni/Pt(l 11) at room temperature (RT). Because the lattice constants of Co and Ni are only slightly different, both growth modes have similar behavior. They grow 2 ML in layer-by-layer mode then turn to 3-D island growth. On the contrary, the magnetic properties have great difference. For Ni/1 ML Co/Pt (111), the easy axis of magnetization changed from the canted state to the out-of-plane direction when the Co buffer layer was inserted into Ni/Pt(111). The perpendicular magnetization persisted to 24 ML of Co thin films. This spin reorientation transition can be understood by the change of effective interface magnetic anisotropy. For Co/1 ML Ni/Pt(111), Kerr signal was not observed when the thickness of Co film was below 3 ML, and the easy axis of the magnetization was in-plane when the thickness of Co was greater than 3 ML at RT. The polar Kerr signal appeared after the sample was annealed at 450 K for 1 ML of Co. Further studies in the magnetic properties and surface composition of 3 ML Co/1 ML Ni/Pt(111) during an annealing process showed that the out-of-plane magnetization enhanced significantly when Co and Ni atoms diffused into the Pt substrate. The Curie temperature (T_c) of both systems can be adjusted by changing the annealing temperature. Measuring at RT, T_c decreased when the annealing temperature rose. However, the change rates were different in these two mirror systems. The possible mechanism of the evolution in the magnetic property with the interface structure was comparatively discussed.