447 research outputs found
Low-temperature specific heat for ferromagnetic and antiferromagnetic orders in CaRu1-xMnxO3
Low-temperature specific heat of CaRu1-xMnxO3 was measured to clarify the
role of d electrons in ferromagnetic and antiferromagnetic orders observed
above x=0.2. Specific heat divided by temperature C_p/T is found to roughly
follow a T^2 function, and relatively large magnitudes of electronic specific
heat coefficient gamma were obtained in wide x range. In particular, gamma is
unchanged from the value at x=0 (84 mJ/K^2 mol) in the paramagnetic state for
x<=0.1, but linearly reduced with increasing x above x= 0.2. These features of
gamma strongly suggest that itinerant d electrons are tightly coupled with the
evolution of magnetic orders in small and intermediate Mn concentrations.Comment: 4 pages, 2 figures, to be published in J. Phys.: Conf. Ser. (SCES
2011, Cambridge, UK
Temperature Dependent Polarized XANES Spectra for Zn-doped LSCO system
The cuprates seem to exhibit statistics, dimensionality and phase transitions
in novel ways. The nature of excitations [i.e. quasiparticle or collective],
spin-charge separation, stripes [static and dynamics], inhomogeneities,
psuedogap, effect of impurity dopings [e.g. Zn, Ni] and any other phenomenon in
these materials must be consistently understood. Zn-doped LSCO single crystal
were grown by TSFZ technique. Temperature dependent Polarized XANES [near edge
local structure] spectra were measured at the BL13-B1 [Photon Factory] in the
Flourescence mode from 10 K to 300 K. Since both stripes and nonmagnetic Zn
impurities substituted for Cu give rise to inhomogeneous charge and spin
distribution it is interesting to understand the interplay of Zn impurities and
stripes. To understand these points we have used Zn-doping and some of the
results obtained are as follows: The spectra show a strong dependence with
respect to the polarization angle, , as is evident at any temperature
by comparing the spectra where the electric field vector is parallel with
ab-plane to the one where it is parallel to the c-axis. By using the XANES
[temperature] difference spectra we have determined T* [experimentally we find,
T* 160-170 K] for this sample. The XANES difference spectra shows
that the changes in XANES features are larger in the ab-plane than the c-axis,
this trend is expected since zinc is doped in the ab-plane at the copper site.
Our study also complements the results in literature namely that zinc doping
does not affect the c-axis transport.Comment: To appear in Physica C [ISS2001 Special Issue], related talk
presented at ISS2001 as PC-16, 10 pages revtex and 7 pages of figures (pdf
Clear Experimental Signature of Charge-Orbital density wave in NdCaMnO
Single Crystals of NdCaMnO have been prepared by the
travelling floating-zone method, and possible evidence of a charge -orbital
density wave in this material presented earlier [PRB68,092405 (2003)] using
High Resolution Electron Microscopy [HRTEM] and Electron Diffraction [ED]. In
the current note we present direct evidence of charge-orbital ordering in this
material using heat capacity measurements. Our heat capacity measurements
indicate a clear transition consistent with prior observation. We find two main
transitions, one at temperature K, and other at
K. In addition, we may also conclude that there is a strong electron-phonon
coupling in this material.Comment: 7 pages, 8 figure
A Component Based Heuristic Search Method with Evolutionary Eliminations
Nurse rostering is a complex scheduling problem that affects hospital
personnel on a daily basis all over the world. This paper presents a new
component-based approach with evolutionary eliminations, for a nurse scheduling
problem arising at a major UK hospital. The main idea behind this technique is
to decompose a schedule into its components (i.e. the allocated shift pattern
of each nurse), and then to implement two evolutionary elimination strategies
mimicking natural selection and natural mutation process on these components
respectively to iteratively deliver better schedules. The worthiness of all
components in the schedule has to be continuously demonstrated in order for
them to remain there. This demonstration employs an evaluation function which
evaluates how well each component contributes towards the final objective. Two
elimination steps are then applied: the first elimination eliminates a number
of components that are deemed not worthy to stay in the current schedule; the
second elimination may also throw out, with a low level of probability, some
worthy components. The eliminated components are replenished with new ones
using a set of constructive heuristics using local optimality criteria.
Computational results using 52 data instances demonstrate the applicability of
the proposed approach in solving real-world problems.Comment: 27 pages, 4 figure
An effective spin-orbital Hamiltonian for the double perovskite SrFeW O: Derivation of the phase diagram
We formulate a superexchange theory of insulating double-perovskite compounds
such as SrFeWO. An effective spin-orbital Hamiltonian is derived in the
strong coupling limit of Hubbard model for d-electrons on Fe and W ions. The
relevant degrees of freedom are the spins S=2 and the three-fold orbital
degeneracy of Fe-ions. W-sites are integrated out by means of a
fourth-order perturbative expansion. The magnetically and orbitally ordered
ground states of the effective Hamiltonia n are discussed as a function of the
model parameters. We show that for realistic values of such parameters the
ground state is antiferromagnetic, as experimentally observed. The order found
is of type-II, consisting of \{111\} ferromagnetic planes stac ked
antiferromagnetically. The orbital order energy scale found is one order of
magnitude less than the spi n one.Comment: 12 pages, 4 figure
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