Abstract-A process based on argon sputtering has been developed for the production of Pt/Co multilayers with high coercivities. Loop squareness and polar Kerr rotation are not degraded by the processing and multilayers with square loops, polar Kerr rotations of >0.3 0 and coercivities approaching 6 kOe have been prepared. KEYWORDS: PT/CO, MULTILA YERS, mGH COERCIVITY, ARGON SPUTTERING
INTRODUCfIONPt/Co multilayers are widely recognised as promising next generation media for magneto-optical recording due to their large Kerr rotation at short wavelengths and their excellent corrosion resistance [1,2]. Key improvements in materials properties are still required if the system is to be commercialised, including a simple means of producing multilayers with a sufficiently large coercivity which can be read and written through the substrate. Early work on sputtered Pt/Co multilayers achieved coercivities up to around 1.5 kOe, compared to 5 to 10 kOe for the RE-TM media. Hashimoto, et al [3], found that relatively high coercivities could be produced by growing the multilayer on thick metal underlayers and at high sputtering pressures. However, such multilayers are impractical for use in a conventional magneto-optical disk drive since the magneto-optic film could not be addressed through the substrate. Further progress was made by Lee, [4] et al who used molecular beam epitaxy to produce Pt/Co multilayers with square loop coercivities of over 3 kOe. Such a result confirmed the potential for high coercivities from the Pt/Co multilayer system. Carcia, et al [5] developed a sputtering process which used heavier krypton or xenon as the sputtering gases instead of argon, and which, when used to deposit Pt/Co multilayers on an oxide undedayer [6], gave multilayers with square loop coercivities of over 3 kOe. More recently, Weller, et al, [7], have obtained a similar high coercivity using argon sputtering onto SiNx buffer layers. However, the high pressures used resulted in a porous and granular microstructure.There is still a need for a simple deposition process, incorporating argon sputtering, which can produce high coercivity Pt/Co multilayers with a high polar Kerr rotation. We report here work on the preparation of Pt/Co multjlayers with coercivities approaching 6 kOe and polar Kerr rotations of over 0.3°, optically addressable through the substrate.
EXPERIMENTALPt/Co multilayer structures were produced in a modified Nordiko NS 3750 magnetron sputtering machine using dual source deposition. All films were produced using argon as the sputter gas. Pt/Co individual layer thicknesses were confirmed using X-ray diffraction and Inductively Coupled Plasma Emission Spectrometry. It is intended to publish separately full details of the multilayer preparation process.Magneto-optic measurements were performed using a custom-built polar Kerr loop tracer. Micromagnetic and microstructural measurements were undertaken using a transmlSSlon electron microscope, using Lorentz microscopy for domain observations, by the method reported by Cha...
