VNU-UET Repository: No conditions. Results ordered -Date Deposited. 2024-03-29T13:46:46ZEPrintshttp://eprints.uet.vnu.edu.vn/images/sitelogo.pnghttps://eprints.uet.vnu.edu.vn/eprints/2016-07-06T06:35:15Z2017-06-15T01:55:53Zhttp://eprints.uet.vnu.edu.vn/eprints/id/eprint/1797This item is in the repository with the URL: http://eprints.uet.vnu.edu.vn/eprints/id/eprint/17972016-07-06T06:35:15ZCritical Behavior of La0.7Ca0.3MnO3 NanoparticlesWe used the modified Arrott plot method to analyze magnetic-field dependences of magnetization, M(H), around the ferromagneticparamagnetic
(FM-PM) phase-transition temperature (TC) of three nanocrystalline La0.7Ca0.3MnO3 samples with average crystallite sizes d = 40,
23, and 16 nm. The analyses obtained the values of critical parameters to be TC µ 261 K, ¢ = 0.485 « 0.005, £ = 1.051 « 0.094 and ¤ = 3.1 «
0.1 for the sample with d = 40 nm, TC µ 252 K, ¢ = 0.525 « 0.010, £ = 0.893 « 0.139 and ¤ = 2.7 « 0.1 for d = 23 nm, and TC µ 236 K,
¢ = 0.621 « 0.008, £ = 0.825 « 0.007 and ¤ = 2.2 « 0.2 for d = 16 nm. With these critical values, the M(H) data points around TC of the
samples fall into two universal branches of a scaling function M(H, ¾) = «¾«
¢f«(H/«¾«
¢+£
), with ¾ = (T ¹ TC)/TC, f+ for T > TC and f¹ for T < TC.
The results reveal that the crystallite-size reduction of nanoparticles decreases the TC value. This is ascribed to the decrease of FM doubleexchange
interactions between Mn3+ and Mn4+ ions, which is related to the ¢ change from 0.485 for d = 40 nm to 0.621 for d = 16 nm,
corresponding to the change in FM order from the long-range type to the short-range one.A. Ho T.D. Thanh T.V. Manh T.O. Ho T.Duc Thang Phampdthang@vnu.edu.vnL. Phan T.C. Yu S.2016-07-06T06:33:35Z2016-07-06T06:35:07Zhttp://eprints.uet.vnu.edu.vn/eprints/id/eprint/1796This item is in the repository with the URL: http://eprints.uet.vnu.edu.vn/eprints/id/eprint/17962016-07-06T06:33:35ZLocal geometric and electronic structures and origin of magnetism in Co-doped BaTiO3 multiferroicsWe have prepared polycrystalline samples BaTi1−xCoxO3 (x = 0–0.1) by solid-state reaction. X-ray diffraction and Raman-scattering studies reveal the phase separation in crystal structure as changing Co-doping content (x). The samples with x = 0–0.01 are single phase in a tetragonal structure. At higher doping contents (x > 0.01), there is the formation and development of a secondary hexagonal phase. Magnetization measurements at room temperature indicate a coexistence of paramagnetic and weak-ferromagnetic behaviors in BaTi1−xCoxO3 samples with x > 0, while pure BaTiO3 is diamagnetic. Both these properties increase with increasing x. Analyses of X-ray absorption spectra recorded from BaTi1−xCoxO3 for the Co and Ti K-edges indicate the presence of Co2+ and Co3+ ions. They locate in the Ti4+ site of the tetragonal and hexagonal BaTiO3 structures. Particularly, there is a shift of oxidation state from Co2+ to Co3+ when Co-doping content increases. We believe that the paramagnetic nature in BaTi1−xCoxO3 samples is due to isolated Co2+ and Co3+ centers. The addition of Co3+ ions enhances the paramagnetic behavior. Meanwhile, the origin of ferromagnetism is due to lattice defects, which is less influenced by the changes caused by the variation in concentration of Co2+ and Co3+ ions.
The-Long , P. D. Thang2, T. A. 1, T. V. Manh1, Tran Dang Thanh1,3, V. D. Lam3, N. T. Dang4 and S. C. YuThe Long PhanDuc Thang Phampdthang@vnu.edu.vnA. Ho T.V. Manh T.Dang Thanh TranD. Lam VT. Dang N.C. Yu S.