Proceedings of Magneto-Optical Recording International Symposium '96, J. Magn. Soc. Jpn., Vo!. 20, Supplement No. SI (1996), pp. 451-454 © 1996 by The Magnetics Society of Japan ANISOTROPY AND MAGNETO-OPTICAL KERR SPECTRA OF CaxNiI-x/Au MULTILA YERS R. Krishnan, M. Seddat, M. Porte and M. Tessier Laboratoire de Magnetisme et d'Optique, URA 1531, C.N.R.S. 92195 Meudon, France M. Nyvlt and S. Visnovsky . Institute of Physics, Charles University, Ke Karlvou 5, 12116 Prague, Czech Repubbc 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. KEY WORDS: MULTILA YERS, MAGNETO-OPTICAL PROPERTIES, SURFACE ANISOTROPY. Magnetic multilayers are new class of materials with novel properties .. One of the most promising applications of magnetic multi layers (ML) is for magneto-optic (MO) storage media. The typical examples such as Co/Pt and Co/Pd, by virtue of their strong uniaxial anisotropy and good magneto-optical effects, are potential candidates for MO storage applications in the blue light wavelength and hence have attracted much attention from several research groups [1,2,3]. Hashimoto et al [4] have carried out actual recording on Co/Pt discs at a wavelength of 488 nm. New class of materials based on Co-Ni/Pt instead of pure Co/Pt have also been proposed recently [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 DETAILS The 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 deter- mined 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 pro- perties 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 anisotropy 0.5 N E 01 ..... Q) III 0 Fig. 1 The variation of Ks as a function of Co content (x) at SK. 45]