ANISOTROPY AND MAGNETO-OPTICAL KERR SPECTRA OF CaXNi1-X/Au MULTILAYERS

Abstract

Abstract:We have prepared CaxNi I-x/Au multi layers by evaporation and studied their magnetic properties and magneto-optical Kerr spectra. With the addition of Co the surface anisotropy increases linearly and stabilises the perpendicular magnetisation. For x= 0.7 the sample with magnetic layer thickness of 5.4 A shows a rectangular loop with a maximum coercivity of 800 Oe. For thinner Co-Ni layers the Kerr peak due to the interband transitions of Au is clearly seen but for thicker layers it is the CO-Ni like behaviour. The spectra could be well explained by the electromagnetic model. [5,6,7] which show similar properties as Co/Pt but with a relatively lower Curie temperature of the order of 250°C. Writing at such temperatures is far more safer and will not cause any interfacial diffusion. This point is of great importance for application. We showed that the surface anisotropy (Ks ) in this system varied linearly with the Co concentration which is of fundamental importance as we have discussed in our work [6]. We attributed this behaviour also to the fact that the magneto-elastic contribution to Ks is negligible if not absent. It was interesting to study other systems to verify this conclusion and we chose the system based on Au, since Co/Au has been intensely studied in the past [8,9]. We had shown that in Ni/Au multi layers where Ks is negative which is rather unusual [10]. We describe in this work the magnetic and the magneto-optical properties of (Co x Nil-x)/Au multi layers prepared by evaporation. EXPERIMENTAL DETAILSThe multilayers were prepared by sequential evaporation using a dual e-beam under ultra high vacuum conditions. The details of the deposition can be found in rer. 2. For depositing Cox Nil-x alloy layers, we first prepared an alloy ingot and used it as a source. We have subsequently determined the composition by analysing 1500 A thick layer. No difference in the composition between the source and the layer could be detected. Both glass and silicon were used as substrates. First Au buffer layer 100 A thick was deposited at room temperature and then annealed at 200°C for 2 hours. The multilayers were then grown on this buffer layer at room temperature. The Au layer thickckness t(Au) was kept constant at 15 A and that of Co-Ni was varied in the range 4 to 30 A.The growth parameters will be designated as {t(Co,Ni), t(Au)} x N where N stands for the number of bilayers. The top layer was Au layer 20 A thick which also served as a protective layer.Low and high angle X-ray diffraction studies were made to verify the periodic structure and to calculate the layer thicknesses. Magnetization was measured using a vibrating sample magnetometer (VSM) and the anisotropy was determined by a home made sensitive torque meter. The above properties were measured in the temperature range 6 to 300K. Magneto-optical polar Kerr spectra were studied at 295 K in the photon energy range from 1.5 to 5.2 eV. Kerr loops were also taken. RESULTS AND DISCUSSIONS Magnetic anisotropy0.5