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Nanotechnology 25 165601. (2014).
Fu-Te Yuan1, An-Cheng Sun2, C F Huang2 and Jen-Hwa Hsu3
1 iSentek Ltd, Advanced Sensor Laboratory, New Taipei City 22101, Taiwan and
2 Department of Chemical Engineering and Materials Science, Yuan Ze University, Taoyuan 320, Taiwan and
3 Department of Physics, National Taiwan University, Taipei 106, Taiwan.
Abstract
Ultrathin percolated high-Ku magnetic films with thicknesses of 2 nm are realized simply by using sputter deposition and post annealing. L11 CoPt:MgO, with Ku on the order of 107 erg cm−3, was deposited on a MgO(111) substrate at 350 °C, followed by post annealing to induce complete segregation of the added MgO dopants. The optimized film shows significant enhancement of the out-of-plane coercivity, approximately an order of magnitude greater than that of the CoPt binary film, a remanence ratio close to unity, considerably reduced in-plane magnetization, sharp perpendicular magnetic reversal, and reduced surface roughness in the range of a few angstroms. Microstructure results indicate that MgO precipitates into grains within the interconnected L11 grains after appropriate post annealing. The MgO grains, with sizes in the range 2–7 nm, form coherent interfaces to the CoPt matrix and penetrate through the whole depth of the film. The development of ideal non-magnetic domain wall pinning sites explains the optimization of the perpendicular magnetic properties. The advantages of a simple fabrication process, a thin film layer structure, and remarkable enhancement of the magnetic characteristics demanded by ultrahigh-density recording reveal its potential for practical applications.
Significance Statement
Ultrathin percolated high Ku magnetic films with thicknesses of 2 nm are realized simply by using sputter deposition and post annealing. L11 CoPt:MgO, with Ku on the order of 107 erg/cm3, was deposited on a MgO(111) substrate at 350oC, followed by post annealing to induce complete segregation of the added MgO dopants. The optimized film shows significant enhancement of the out-of-plane coercivity, approximately an order of magnitude greater than that of the CoPt binary film, a remanence ratio close to unity, considerably reduced in-plane magnetization, sharp perpendicular magnetic reversal, and reduced surface roughness in the range of a few angstroms. Microstructure results indicate that MgO precipitates into grains within the interconnected L11 grains after appropriate post annealing. The MgO grains, with sizes in the range 2-7 nm, form coherent interfaces to the CoPt matrix and penetrate through the whole depth of the film. The development of ideal nonmagnetic domain wall pinning sites explains the optimization of the perpendicular magnetic properties. The advantages of a simple fabrication process, a thin film layer structure, and remarkable enhancement of the magnetic characteristics demanded by ultrahigh density recording reveal its potential for practical applications.
