Annealing Study of (Co/Pd) N Magnetic Multilayers for Applications in Bit-Patterned Magnetic Recording Media
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0961-O01-06
Annealing Study of (Co/Pd) N Magnetic Multilayers for Applications in Bit-Patterned Magnetic Recording Media Chunsheng E.1, James Rantschler1, Shishan Zhang2, T. Randall Lee2, Darren Smith3, Dieter Weller4, Sakhrat Khizroev5, and Dmitri Litvinov1,6 1 Electrical & Computer Engineering, University of Houston, Houston, TX, 77204 2 Chemistry, University of Houston, Houston, TX, 77204 3 Materials Engineering, University of Houston, Houston, TX, 77204 4 Seagate, Fremont, TX, 94538 5 Electrical Engineering, University of California - Riverside, Riverside, CA, 92521 6 Chemical & Biomolecular Engineering, University of Houston, Houston, TX, 77204
ABSTRACT This work presents an annealing study of high-anisotropy (Co/Pd)N magnetic multilayers designed for bit-patterned medium recording applications. Magnetic multilayers were deposited by magnetron sputtering at 2.5mT argon pressure at room temperature and annealed at different temperatures (up to 250oC) for up to 2 hours in atmosphere and in vacuum. Depending on the annealing time, the samples annealed in atmosphere exhibited two distinct modes of magnetization reversal. In samples annealed for a time shorter than some critical time, tc, where tc is a function of the annealing temperature, the magnetization reversal occurs by domain wall injection and propagation. In samples annealed for times longer then tc, the magnetization reversal mode switches to magnetization rotation. Using XPS, it is found that the transition is accompanied by the formation of oxidizes at the grain boundaries leading to exchange decoupling of the grains. In samples annealed at higher temperatures, the increases of the coercivity of as high as 30 times the coercivity of as prepared samples are observed. Significantly, annealing in vacuum showed only small modification of magnetic properties as manifested by relatively minor modifications of vertical M-H loops and unchanged morphology of domain patterns in ac demagnetized state.
INTRODUCTION High magnetic anisotropy multilayer thin films such as (Co/Pd)N and (Co/Pt)N have been studied extensively as candidates for recording layers in magnetic and magneto-optical recording schemes including bit-patterned medium [1-4]. Perpendicular magnetic anisotropy in these multilayers results from the interfacial effects between Co and Pd layers; the control of these interfaces being at the focus of material development. Various parameters control the quality of the interfaces including stress due to lattice mismatch. During annealing, the mobility of the atoms increases, which can result in intermixing of Co and Pd atoms at the interfaces, the relaxation of lattice stress, or both depending on the annealing conditions. Den Broeder et. al. [5] reported that when (Co/Pd)N multilayer films are annealed at 350 ºC for up to 8 hours, the uniaxial anisotropy constant KU, the remnance ratio Mr/Ms and coercivity HC decrease monotonically with the annealing time. The changes in KU, Mr/MS and HC have the same trends
for (Co/Pd)N multilayer exposed to ion irrad
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