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RISS 인기검색어
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- 저자 : V. Ström (검색결과 2 건)
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V. Ström,K.S. Kim,B.J. Jönsson,S.C. Yu,A. Inoue,K.V. Rao 한국자기학회 1995 韓國磁氣學會誌 Vol.5 No.5
We have studied the magnetization in fields up to IT at 5K, the saturation magnetization dependence on temperature and the temperature dependence of AC-susceptibility at very low fields (5mOe to 50mOe) of glassy Fe_(91-x)Zr_7B₂Ni_x (x = 0, 5, 10, 15) alloys. The temperature dependence of the magnetization follows the predictions of spin wave excitations with long wavelengths. At zero Ni concentration there is a clear competition between ferromagnetic and antiferromagnetic interactions giving rise to spin-glass behaviour. The addition of Ni drastically modifies the magnetic properties: the antiferromagnetic exchange coupling is reduced and finally disappears, the spin wave stiffness increases from 39.5 to 87.3 meVŲ and Tc increases from 230 K to 478 K. We develop a simple model to quantify the competing interactions and to relate the antiferromagnelically coupled Fe moments to the Ni concentration. We find that the initial susceptibility increases with increasing Ni content along with a decrease of the temperature dependence.
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MAGNETISM OF NANOPHASE IRON PARTICLES LASER EVAPORATED IN A CONTROLLED OXYGEN ATMOSPHERE
T. Turkki,B.J. Jönsson,V. Ström,H. Medelius,M.S. El-Shall,K.V. Rao 한국자기학회 1995 韓國磁氣學會誌 Vol.5 No.5
Magnetic nanoparticles of iron and iron oxide have been prepared in a modified upward thermal diffusion cloud chamber using pulsed laser evaporation. SEM/TEM studies of these particles reveal a size distribution with a mean diameter of about 60 Å. FTIR spectrum measurements are used to investigate the difference in oxidation level between nanoparticles prepared at different partial oxygen pressures. The complex magnetic behaviour of these particles was studied using DC- and AC-susceptibility measurements. All samples exhibit superparamagnetism with blocking temperatures ranging from 50 K to above room temperature. The coercivity fields as well as the dependence of the blocking temperature on measuring frequency have been studied. Magnetic anisotropy constants are found to be one order of magnitude higher than is known for the bulk values. The mean particle size estimated from the magnetic data is found to be in perfect agreement with the TEM observations.
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