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51.
Grazioli C Alfè D Krishnakumar SR Sen Gupta S Veronese M Turchini S Bonini N Dal Corso A Sarma DD Baroni S Carbone C 《Physical review letters》2005,95(11):117201
The occurrence of a noncollinear magnetic structure at a Mn monolayer grown epitaxially on Fe(100) is predicted theoretically, using spinor density-functional theory, and observed experimentally, using x-ray magnetic circular dichroism (XMCD) and linear dichroism (XMLD) spectroscopies. The combined use of XMCD and XMLD at the Mn-absorption edge allows us to assess the existence of ferromagnetic and antiferromagnetic order at the interface, and also to determine the moment orientations with element specificity. The experimental results thus obtained are in excellent agreement with the magnetic structure determined theoretically. 相似文献
52.
Disordered RKKY lattice mean field theory for ferromagnetism in diluted magnetic semiconductors 总被引:1,自引:0,他引:1
We develop a lattice mean field theory for ferromagnetic ordering in diluted magnetic semiconductors by taking into account the spatial fluctuations associated with random disorder in the magnetic impurity locations and the finite mean free path associated with low carrier mobilities. Assuming a carrier-mediated indirect RKKY exchange interaction among the magnetic impurities, we find substantial deviation from the extensively used continuum Zener model Weiss mean field predictions. Our theory allows accurate analytic predictions for Tc and provides simple explanations for a number of observed anomalies, including the non-Brillouin function magnetization curves, the suppressed low-temperature magnetization saturation, and the dependence of Tc on conductivity. 相似文献
53.
Sarma DD Topwal D Manju U Krishnakumar SR Bertolo M La Rosa S Cautero G Koo TY Sharma PA Cheong SW Fujimori A 《Physical review letters》2004,93(9):097202
We use a spatially resolved, direct spectroscopic probe for electronic structure with an additional sensitivity to chemical compositions to investigate high-quality single crystal samples of La(1/4)Pr(3/8)Ca(3/8)MnO3, establishing the formation of distinct insulating domains embedded in the metallic host at low temperatures. These domains are found to be at least an order of magnitude larger in size compared to previous estimates and exhibit memory effects on temperature cycling in the absence of any perceptible chemical inhomogeneity, suggesting long-range strains as the probable origin. 相似文献
54.
Congeduti A Postorino P Caramagno E Nardone M Kumar A Sarma DD 《Physical review letters》2001,86(7):1251-1254
Raman spectra of La(0.75)Ca(0.25)MnO(3) have been collected for the first time over a wide pressure range (0-14 GPa) using a diamond anvil cell. The frequency range explored (200-1100 cm(-1)) and the very good quality of the data allowed us to carefully analyze the pressure evolution of the phonon modes of the MnO(6) octahedra. The results show an abrupt transition at approximately 7.5 GPa with an evident deviation from the linear trend of the frequency of the Jahn-Teller phonon versus the applied pressure, accompanied by a strong phonon broadening. This behavior disagrees with the predicted insulator to metal transition and, on the contrary, indicates the occurrence of a new unpredicted phase in the very high pressure regime. 相似文献
55.
We investigate, by numerically calculating the charge stiffness, the effects of random diagonal disorder and electron-electron interaction on the nature of the ground state in the 2D Hubbard model through the finite-size exact diagonalization technique. By comparing with the corresponding 1D Hubbard model results and by using heuristic arguments we conclude that it is unlikely that there is a 2D metal-insulator quantum phase transition, although the effect of interaction in some range of parameters is to substantially enhance the noninteracting charge stiffness. 相似文献
56.
57.
Earlier we reported an ion current jump which was observed at a fixed negative biased disc potential in the 6.4GHz ECR ion source at VECC,Kolkata.In a recent experiment with neon ions,we measured the time spectra of the ion current and observed the presence of a burst frequency in the kilohertz range.This frequency shows a correlated jump with the ion current jump described above.Another interesting feature is that the observed burst frequency shows a good linear correlation with the extracted ion current.The higher the ion current,the higher is the burst frequency.This means that current per burst is a constant factor;when there are more number of bursts,the current also increases. 相似文献
58.
Y. Rama Krishna Sarma 《Annals of the Institute of Statistical Mathematics》1987,39(1):497-512
Summary In this note some asymptotically optimum tests for testing hypotheses concerning parameters when the observations are dependent
are obtained. Test statistics based on the score functions, similar to the one proposed by Rao in the case when the observations
are i.i.d. are proposed. Asymptotically UMP tests for one sided hypotheses against one sided alternatives and asymptotically
UMP unbiased test for a simple hypothesis against two sided alternatives are derived. In the multiparameter case tests for
simple hypotheses that have asymptotically best constant power on some family of surfaces in the parameter space are derived. 相似文献
59.
Biswanath Das Kongara Ravinder Reddy Bommena Ravikanth Akella Venkata Subrahmanya Sarma Balasubramanian Sridhar 《Helvetica chimica acta》2008,91(6):1137-1143
Chemical investigation on two samples of the flowers of Parthenium hysterophorus afforded two new pseudoguaianolides (one from each sample) together with several known constituents. The structures of the new compounds were established by extensive spectroscopic (1D‐ and 2D‐NMR) studies. The X‐ray crystallographic analysis of one of these compounds was also accomplished. 相似文献
60.
The data on the excitation functions of20Ne(16O,12C)24Mg,20Ne(16O,12C)24Mg*(1.37, 2+),20Ne(16O,12C)24Mg*(4.12, 4++4.24, 2+) +20Ne(16O,12C*(4.44, 2+))24Mg,20Ne(16O,12C)24Mg*(6.01, 4++6.43, 0+),20Ne(16O,20Ne)16O,20Ne(16O,20Ne*(1.63, 2+))16O, and20Ne(16O,20Ne*(4.25, 4+))16O reactions atθ lab=13° fromE c.m.=22.8 to 38.6 MeV have been subjected to a statistical analysis comprising of the calculations of the distribution of cross sections, deviation functions, cross-correlation functions, summed excitation functions, cross-channel correlation coefficients and coherence widths. The analysis confirms the existence of nonstatistical structures atE c.m.=24.6, 27.8, 31.7 and 35.5 MeV, and identifies a new structure of the same nature atE c.m. =25.6 MeV. 相似文献