3,866 research outputs found

### Nanoscale magnetic structure of ferromagnet/antiferromagnet manganite multilayers

Polarized Neutron Reflectometry and magnetometry measurements have been used
to obtain a comprehensive picture of the magnetic structure of a series of
La{2/3}Sr{1/3}MnO{3}/Pr{2/3}Ca{1/3}MnO{3} (LSMO/PCMO) superlattices, with
varying thickness of the antiferromagnetic (AFM) PCMO layers (0<=t_A<=7.6 nm).
While LSMO presents a few magnetically frustrated monolayers at the interfaces
with PCMO, in the latter a magnetic contribution due to FM inclusions within
the AFM matrix was found to be maximized at t_A~3 nm. This enhancement of the
FM moment occurs at the matching between layer thickness and cluster size,
where the FM clusters would find the optimal strain conditions to be
accommodated within the "non-FM" material. These results have important
implications for tuning phase separation via the explicit control of strain.Comment: 4 pages, submitted to PR

### The information paradox: A pedagogical introduction

The black hole information paradox is a very poorly understood problem. It is
often believed that Hawking's argument is not precisely formulated, and a more
careful accounting of naturally occurring quantum corrections will allow the
radiation process to become unitary. We show that such is not the case, by
proving that small corrections to the leading order Hawking computation cannot
remove the entanglement between the radiation and the hole. We formulate
Hawking's argument as a `theorem': assuming `traditional' physics at the
horizon and usual assumptions of locality we will be forced into mixed states
or remnants. We also argue that one cannot explain away the problem by invoking
AdS/CFT duality. We conclude with recent results on the quantum physics of
black holes which show the the interior of black holes have a `fuzzball'
structure. This nontrivial structure of microstates resolves the information
paradox, and gives a qualitative picture of how classical intuition can break
down in black hole physics.Comment: 38 pages, 7 figures, Latex (Expanded form of lectures given at CERN
for the RTN Winter School, Feb 09), typo correcte

### Giant electrocaloric effect in thin film Pb Zr_0.95 Ti_0.05 O_3

An applied electric field can reversibly change the temperature of an
electrocaloric material under adiabatic conditions, and the effect is strongest
near phase transitions. This phenomenon has been largely ignored because only
small effects (0.003 K V^-1) have been seen in bulk samples such as
Pb0.99Nb0.02(Zr0.75Sn0.20Ti0.05)0.98O3 and there is no consensus on macroscopic
models. Here we demonstrate a giant electrocaloric effect (0.48 K V^-1) in 300
nm sol-gel PbZr0.95Ti0.05O3 films near the ferroelectric Curie temperature of
222oC. We also discuss a solid state device concept for electrical
refrigeration that has the capacity to outperform Peltier or magnetocaloric
coolers. Our results resolve the controversy surrounding macroscopic models of
the electrocaloric effect and may inspire ab initio calculations of
electrocaloric parameters and thus a targeted search for new materials.Comment: 5 pages, 4 figure

### The structure of intercalated water in superconducting Na$_{0.35}$CoO$_{2}\cdot$1.37D$_{2}$O: Implications for the superconducting phase diagram

We have used electron and neutron powder diffraction to elucidate the
structural properties of superconducting \NaD. Our measurements show that our
superconducting sample exhbits a number of supercells ranging from ${1/3}a^{*}$
to ${1/15}a^{*}$, but the most predominant one, observed also in the neutron
data, is a double hexagonal cell with dimensions \dhx. Rietveld analysis
reveals that \deut\space is inserted between CoO$_{2}$ sheets as to form a
layered network of NaO$_{6}$ triangular prisms. Our model removes the need to
invoke a 5K superconducting point compound and suggests that a solid solution
of Na is possible within a constant amount of water $y$.Comment: 4 pages, 3 figure

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