2,228 research outputs found
Room-temperature ferromagnetism in nanoparticles of superconducting materials
Nanoparticles of superconducting YBa2Cu3O7-delta (YBCO) (Tc = 91 K) exhibit
ferromagnetism at room temperature while the bulk YBCO, obtained by heating the
nanoparticles at high temperature (940 degree C), shows a linear magnetization
curve. Across the superconducting transition temperature, the magnetization
curve changes from that of a soft ferromagnet to a superconductor. Furthermore,
our experiments reveal that not only nanoparticles of metal oxides but also
metal nitrides such as NbN (Tc = 6 - 12 K) and delta-MoN (Tc ~ 6 K) exhibit
room-temperature ferromagnetism.Comment: 11 pages, 6 figure
The structure of two new non-centrosymmetric phases of oxygen deficient bismuth manganite
The structure of two new phases in the bismuth manganite system are reported. The phases were determined by electron diffraction studies of two oxygen-deficient bulk samples. The first phase, a minority component of bulk BiMnO2.94 forms a n=2 Ruddlesden-Popper phase with space group Cmc21 . The second phase, from bulk BiMnO2.99 , is an orthorhombic structure
with spacegroup Pmn21 and a unit cell approximately equal to 4 × √ 2 × 2 √ 2 times the parent perovskite cell. Importantly both phases are non-centrosymmetric and offer further potential for multiferroic studies.The authors would like to thank EPSRC for financial support for this work through grant EP/H017712
Valence instability of cerium under pressure in the Kondo-like perovskite LaCeSrMnO
Effect of hydrostatic pressure and magnetic field on electrical resistance of
the Kondo-like perovskite manganese oxide,
LaCeSrMnO with a ferrimagnetic ground state, have
been investigated up to 2.1 GPa and 9 T. In this compound, the Mn-moments
undergo double exchange mediated ferromagnetic ordering at
280 K and there is a resistance maximum, at about 130 K which is
correlated with an antiferromagnetic ordering of {\it cerium} with respect to
the Mn-sublattice moments. Under pressure, the shifts to lower
temperature at a rate of d/d = -162 K/GPa and disappears at a
critical pressure 0.9 GPa. Further, the coefficient, of
term due to Kondo scattering decreases linearly with increase of
pressure showing an inflection point in the vicinity of . These
results suggest that {\it cerium} undergoes a transition from Ce state
to Ce/Ce mixed valence state under pressure. In contrast to
pressure effect, the applied magnetic field shifts to higher
temperature presumably due to enhanced ferromagnetic Mn moments.Comment: to be published in Phys. Rev. B (rapid commun
Observation of a dissipative phase transition in a one-dimensional circuit QED lattice
Condensed matter physics has been driven forward by significant experimental
and theoretical progress in the study and understanding of equilibrium phase
transitions based on symmetry and topology. However, nonequilibrium phase
transitions have remained a challenge, in part due to their complexity in
theoretical descriptions and the additional experimental difficulties in
systematically controlling systems out of equilibrium. Here, we study a
one-dimensional chain of 72 microwave cavities, each coupled to a
superconducting qubit, and coherently drive the system into a nonequilibrium
steady state. We find experimental evidence for a dissipative phase transition
in the system in which the steady state changes dramatically as the mean photon
number is increased. Near the boundary between the two observed phases, the
system demonstrates bistability, with characteristic switching times as long as
60 ms -- far longer than any of the intrinsic rates known for the system. This
experiment demonstrates the power of circuit QED systems for studying
nonequilibrium condensed matter physics and paves the way for future
experiments exploring nonequilbrium physics with many-body quantum optics
Can a gravitational wave and a magnetic monopole coexist?
We investigate the behavior of small perturbations around the Kaluza-Klein
monopole in the five dimensional space-time. We find that the even parity
gravitational wave does not propagate in the five dimensional space-time with
Kaluza-Klein monopole provided that the gravitational wave is constant in the
fifth direction. We conclude that a gravitational wave and a U(1) magnetic
monopole do not coexist in five dimensional Kaluza-Klein spacetime.Comment: 10 pages, LaTeX. To appear in Modern Physics Letters
Field-induced Polar Order at the N\'eel Temperature of Chromium in Rare-earth Orthochromites: Interplay of Rare-earth and Cr Magnetism
We report field-induced switchable polarization (P = 0.2 ~ 0.8 microC/cm2)
below the N\'eel temperature of chromium (TN Cr) in weakly ferromagnetic
rareearth orthochromites, RCrO3 (R=rareearth) but only when the rareearth ion
is magnetic. Intriguingly, the polarization in ErCrO3 (TC ~ 133 K) disappears
at a spin reorientation (Morin) transition (TSR ~ 22 K) below which the weak
ferromagnetism associated with the Cr sublattice also disappears, demonstrating
the crucial role of weak ferromagnetism in inducing the polar order. Further,
the polarization (P) is strongly influenced by applied magnetic field,
indicating a strong magneto electric effect. We suggest that the polar order
occurs in RCrO3, due to the combined effect of poling field that breaks the
symmetry and the exchange field on R ion from Cr sublattice stabilizes the
polar state. We propose that a similar mechanism could work in the
isostructural rareearth orthoferrites, RFeO3 as well.Comment: 31 pages (Manuscript(6 figures)+supplemental information(8 figures)
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