High Coercivity Pt/Co Multilayers

Abstract

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...

Stacked Pt/Co Multilayers With Independent Control of Coercivity and Curie Temperature

“…All multilayers were deposited by magnetron sputtering in argon using dual source deposition [2]. In both examples, multilayers 1, 2, la and 2a were deposited separately first onto glass substrates and their polar Kerr loops and Curie temperatures measured.…”

“…A first step towards this would be the preparation of a Pt/Co multilayer structure of similar nature to the direct overwrite (DOW) bilayer first described by Saito et al [1] consisting of a memory layer with a low Curie temperature (Tc) and high ambient coercivity (Hc) and a reference layer with a higher Curie temperature and a lower ambient coercivity. The development at Johnson Matthey of techniques for the preparation of Pt/Co MLs of controlled coercivity [2] gives the potential to address this aim. This paper reports the preparation of stacked Pt/Co MLs with independent control of coercivity and Curie temperature addressable through the substrate.…”