4,403 research outputs found
89Y NMR Probe of Zn Induced Local Magnetism in YBa2(Cu(1-y)Zn(y))3O(6+x)
We present detailed data and analysis of the effects of Zn substitution on
the planar Cu site in YBaCuO (YBCO) as evidenced from
our Y NMR measurements on oriented powders. For we find
additional NMR lines which are associated with the Zn substitution. From our
data on the intensities and temperature dependence of the shift, width, and
spin-lattice relaxation rate of these resonances, we conclude that the spinless
Zn 3 state induces local moments on the near-neighbour () Cu
atoms. Additionally, we conjecture that the local moments actually extend to
the farther Cu atoms with the magnetization alternating in sign at subsequent
sites. We show that this analysis is compatible with ESR data taken on
dilute Gd doped (on the Y site) and on neutron scattering data reported
recently on Zn substituted YBCO. For optimally doped compounds
Y resonances are not detected, but a large % -dependent
contribution to the Y NMR linewidth is evidenced and is also attributed
to the occurence of a weak induced local moment near the Zn. These results are
compatible with macroscopic magnetic measurements performed on YBCO
samples prepared specifically in order to minimize the content of impurity
phases. We find significant differences between the present results on the
underdoped YBCO samples and Al NMR data taken on Al
substituted on the Cu site in optimally doped LaCuO. Further
experimental work is needed to clarify the detailed evolution of the impurity
induced magnetism with hole content in the cuprates.Comment: To be published in EPJB 15 pages of text and figures in eps forma
Coal pump development phase 3
Techniques for achieving continuous coal sprays were studied. Coazial injection with gas and pressure atomization were studied. Coal particles, upon cooling, were found to be porous and fragile. Reactivity tests on the extruded coal showed overall conversion to gases and liquids unchanged from that of the raw coal. The potentials for applications of the coal pump to eight coal conversion processes were examined
Spin liquid behaviour in Jeff=1/2 triangular lattice Ba3IrTi2O9
Ba3IrTi2O9 crystallizes in a hexagonal structure consisting of a layered
triangular arrangement of Ir4+ (Jeff=1/2). Magnetic susceptibility and heat
capacity data show no magnetic ordering down to 0.35K inspite of a strong
magnetic coupling as evidenced by a large Curie-Weiss temperature=-130K. The
magnetic heat capacity follows a power law at low temperature. Our measurements
suggest that Ba3IrTi2O9 is a 5d, Ir-based (Jeff=1/2), quantum spin liquid on a
2D triangular lattice.Comment: 10 pages including supplemental material, to be published in Phys.
Rev. B (Rapid Comm.
Optimising superoscillatory spots for far-field super-resolution imaging
Optical superoscillatory imaging, allowing unlabelled far-field super-resolution, has in recent years become reality. Instruments have been built and their super-resolution imaging capabilities demonstrated. The question is no longer whether this can be done, but how well: what resolution is practically achievable? Numerous works have optimised various particular features of superoscillatory spots, but in order to probe the limits of superoscillatory imaging we need to simultaneously optimise all the important spot features: those that define the resolution of the system. We simultaneously optimise spot size and its intensity relative to the sidebands for various fields of view, giving a set of best compromises for use in different imaging scenarios. Our technique uses the circular prolate spheroidal wave functions as a basis set on the field of view, and the optimal combination of these, representing the optimal spot, is found using a multi-objective genetic algorithm. We then introduce a less computationally demanding approach suitable for real-time use in the laboratory which, crucially, allows independent control of spot size and field of view. Imaging simulations demonstrate the resolution achievable with these spots. We show a three-order-of-magnitude improvement in the efficiency of focusing to achieve the same resolution as previously reported results, or a 26 % increase in resolution for the same efficiency of focusing
Possible spin-orbit driven spin-liquid ground state in the double perovskite phase of Ba3YIr2O9
We report the structural transformation of hexagonal Ba3YIr2O9 to a cubic
double perovskite form (stable in ambient conditions) under an applied pressure
of 8GPa at 1273K. While the ambient pressure (AP) synthesized sample undergoes
long-range magnetic ordering at 4K, the high pressure(HP) synthesized sample
does not order down to 2K as evidenced from our susceptibility, heat capacity
and nuclear magnetic resonance (NMR) measurements. Further, for the HP sample,
our heat capacity data have the form gamma*T+beta*T3 in the temperature (T)
range of 2-10K with the Sommerfeld coefficient gamma=10mJ/mol-Ir K2. The 89Y
NMR shift has no T-dependence in the range of 4-120K and its spin-lattice
relaxation rate varies linearly with T in the range of 8-45K (above which it is
T-independent). Resistance measurements of both the samples confirm that they
are semiconducting. Our data provide evidence for the formation of a 5d based,
gapless, quantum spin-liquid (QSL) in the cubic (HP) phase of Ba3YIr2O9. In
this picture, the T term in the heat capacity and the linear variation of 89Y
1/T1 arises from excitations out of a spinon Fermi surface. Our findings lend
credence to the theoretical suggestion [G. Chen, R. Pereira, and L. Balents,
Phys. Rev. B 82, 174440 (2010)] that strong spin-orbit coupling can enhance
quantum fluctuations and lead to a QSL state in the double perovskite lattice.Comment: 6 pages 5 figure
Bose-Einstein condensation of triplons in the S=1 tetramer antiferromagnet K2Ni2(MoO4)3: A compound close to quantum critical point
The structure of K2Ni2(MoO4)3 consists of S=1 tetramers formed by Ni^{2+}
ions. The magnetic susceptibility chi(T) and specific heat Cp(T) data on a
single crystal show a broad maximum due to the low-dimensionality of the system
with short-range spin correlations. A sharp peak is seen in chi(T) and Cp(T) at
about 1.13 K, well below the broad maximum. This is an indication of magnetic
long-range order i.e., the absence of spin-gap in the ground state.
Interestingly, the application of a small magnetic field (H>0.1 T) induces
magnetic behavior akin to Bose-Einstein condensation (BEC) of triplon
excitations observed in some spin-gap materials. Our results demonstrate that
the temperature-field (T-H) phase boundary follows a power-law
(T-T_{N})propotional to H^(1/alpha) with the exponent 1/alpha close to 2/3, as
predicted for BEC scenario. The observation of BEC of triplon excitations in
small H infers that K2Ni2(MoO4)3 is located in the proximity of a quantum
critical point, which separates the magnetically ordered and spin-gap regions
of the phase diagram.Comment: 5 pages, 5 figures, Accepted in Phys. Rev. B Rapid Communication
Incoherent Effect of Fe and Ni Substitutions in the Ferromagnetic-Insulator La0.6Bi0.4MnO3+d
A comparative study of the effect of Fe and Ni doping on the bismuth based
perovskite La0.6Bi0.4MnO3.1, a projected spintronics magnetic semiconductor has
been carried out. The doped systems show an expressive change in magnetic
ordering temperature. However, the shifts in ferromagnetic transition (TC) of
these doped phases are in opposite direction with respect to the parent phase
TC of 115 K. The Ni-doped phase shows an increase in TC ~200 K, whereas the
Fe-doped phase exhibits a downward shift to TC~95 K. Moreover, the Fe-doped is
hard-type whereas the Ni-doped compound is soft-type ferromagnet. It is
observed that the materials are semiconducting in the ferromagnetic phase with
activation energies of 77 & 82 meV for Fe & Ni-doped phases respectively. In
the presence of external magnetic field of 7 Tesla, they exhibit minor changes
in the resistivity behaviours and the maximum isothermal magnetoresistance is
around -20 % at 125 K for the Ni-phase. The results are explained on the basis
of electronic phase separation and competing ferromagnetic and
antiferromagnetic interactions between the various mixed valence cations.Comment: 18 pages including figure
A Study of Impact of Indian Women Entrepreneur in Small Business Unit & Self Help Group
Women entrepreneurs unlike a struggle before have been accepted and encouraged by extended support from the family and friends. Awareness through media and parents in today’s world wanting the best for their children, irrespective of a girl or a boy has helped in increasing numbers of women entrepreneurs. There is a segment though that is still conservative and with the way the Indians are adapting to the western culture, it is not going to be too long to overcome such social pressures. It is always a great start for any woman who organizes herself and is able to dedicate to it with passion, seek opportunities and aggressively bonds with her decision making. I strongly believe the “Persistence is the key to success. When she is 100% passionate about the product and 10 times more passionate about the business concept, she is in the right directionâ€.Women Entrepreneurs may be defined as the women or a group of women who initiate, organize and operate a business enterprise. Self-Help Group is a small voluntary association of poor people preferably from the same socio-economic back drop. The micro-credit given to them makes them enterprising; it can be all women group, all-men group or even a mixed group. A self-help group (SHG usually composed of 10–20 local women)
A novel seven-level active neutral-point-clamped converter with reduced active switching devices and DC-link voltage
© 1986-2012 IEEE. This paper presents a novel seven-level inverter topology for medium-voltage high-power applications. It consists of eight active switches and two inner flying capacitor (FC) units forming a similar structure as in a conventional active neutral-point-clamped (ANPC) inverter. This unique arrangement reduces the number of active and passive components. A simple modulation technique reduces cost and complexity in the control system design without compromising reactive power capability. In addition, compared to major conventional seven-level inverter topologies, such as the neutral point clamped, FC, cascaded H-bridge, and ANPC topologies, the new topology reduces the dc-link voltage requirement by 50%. This recued dc-link voltage makes the new topology appealing for various industrial applications. Experimental results from a 2.2-kVA prototype are presented to support the theoretical analysis presented in this paper. The prototype demonstrates a conversion efficiency of around 97.2% ± 1% for a wide load range
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