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Structural and Magnetic Phase Transitions of Shape-Memory Ni50Mn25+xGa25-x Alloys with Excess Mn
Nguyen Phu Thuy,Ngo Van Nong,Yeong Der Yao 한국물리학회 2008 THE JOURNAL OF THE KOREAN PHYSICAL SOCIETY Vol.52 No.5
The Mn-excess Ni50Mn25+xGa25-x alloys with 1 < x < 7 were developed to investigate struc- tural transitions and magnetic properties. The martensitic transformation temperature (TM) for the structural transformation from tetragonal to cubic was clearly observed from magnetization, electrical resistivity and X-ray diraction studies as a function of temperature for temperatures be- low 400 K. The TM value increased roughly from 260 K to 355 K with increasing Mn concentration and TM showed an abrupt change at the composition x = 5. For the structural transition, the Curie temperature (TC) decreased slightly from 380 K and was insensitive to variations on the Mn/Ga ratio. During the heating and the cooling processes, the samples showed a temperature hysteresis at and below TM. A magnetic-eld-induced strain (MFIS) of about 0.2 % at an applied magnetic ld of 4.2 kOe was derived by using the martensitic transition temperature for polycrystalline samples. The Mn-excess Ni50Mn25+xGa25-x alloys with 1 < x < 7 were developed to investigate struc- tural transitions and magnetic properties. The martensitic transformation temperature (TM) for the structural transformation from tetragonal to cubic was clearly observed from magnetization, electrical resistivity and X-ray diraction studies as a function of temperature for temperatures be- low 400 K. The TM value increased roughly from 260 K to 355 K with increasing Mn concentration and TM showed an abrupt change at the composition x = 5. For the structural transition, the Curie temperature (TC) decreased slightly from 380 K and was insensitive to variations on the Mn/Ga ratio. During the heating and the cooling processes, the samples showed a temperature hysteresis at and below TM. A magnetic-eld-induced strain (MFIS) of about 0.2 % at an applied magnetic ld of 4.2 kOe was derived by using the martensitic transition temperature for polycrystalline samples.
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).