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Magnetic Properties and Microscopic Structures of Ultrathin Co/p3 × p3 − R30˚-Ag/Si(111) Films
Jyh-Shen Tsay,Tsu-Yi Fu,Chih-Kuei Kao,Xiao-Lan Huang,Jyh-Ron Shue,Wei-Hsiang Chen,Yeong-Der Yao,구현주 한국물리학회 2013 THE JOURNAL OF THE KOREAN PHYSICAL SOCIETY Vol.62 No.12
Combined scanning tunneling microscopy and surface magneto-optic Kerr effect studies were employedto study the relation between magnetic properties and the microscopic interfacial structuresof ultrathin Co/p3×p3−R30˚-Ag/Si(111) films. On the top of p3×p3−R30˚-Ag/Si(111), pureCo clusters formed without disrupting the p3 × p3 − R30˚ structure of the Ag buffer layer. Thegreat strain due to the large mismatch between Co and the substrate influenced the nucleation ofCo atoms to form large clusters. No magnetic hysteresis in the polar configuration was observed forfilms thinner than 10 monolayers. The easy axis of magnetization was in the surface plane. Cappingp3 × p3 − R30˚-Ag on top of the Si(111) surface before the deposition of the Co overlayerscan efficiently reduce the nonferromagnetic Co-Si compound to zero thickness. For Co coveragebetween 2.9 and 4.2 monolayers, a lower Curie temperature was observed in ultrathin films. Due tothe existence of a smooth interface between Co and the p3 × p3 − R30˚-Ag buffer, the coercivityfor Co/p3 × p3 − R30˚-Ag/Si(111) is smaller than that for Co/Si(111).
Enhancement of the Polar Coercive Force for Annealed Co/Ir(111) Ultrathin Films
Wen-Yuan Chan,Du-Cheng Tsai,Wei-Hsiang Chen,Cheng-Hsun-Tony Chang,Jyh-Shen Tsay 한국물리학회 2013 THE JOURNAL OF THE KOREAN PHYSICAL SOCIETY Vol.62 No.12
The alloy formation and the magnetic properties of Co/Ir(111) ultrathin films have been investigated. As the temperature is increased above 400 K, interdiffusion of Co and the Ir substrate occurs. Due to a compositional change in the surface layers, the polar coercive force is greatly enhanced. At temperatures above 600 K, magnetic hysteresis appears only in the polar configuration. Thisshows that the easy axis of the magnetization of Co/Ir(111) may be stabilized in the direction ofthe surface normal by thermal-annealing treatments. From systematic investigations of Co/Ir(111)ultrathin films thinner than 4 monolayers, a magnetic phase diagram has been established. Accordingto the compositional changes and related magnetic properties, the phase diagram can beseparated into three regions. In region I at temperatures below 400 K, Co films are ferromagnetic. In region II where atomic interdiffusion occurs in the surface layers, an enhanced polar coerciveforce is observed. The phase transition from phase I to II is related to the interdiffusion betweenthe Co overlayer and the iridium substrate. In region III for low coverage or at high temperatures,a nonferromagnetic behavior is observed. The phase transition from phase II to III is mainly dueto the reduced atomic percent of cobalt in the Co-Ir alloy and to the lowered Curie temperaturecaused by a reduction in the thickness of the magnetic layers.