1,330 research outputs found
What's nonviolence to do with the European Union?
This is the author accepted manuscript. The final version is available from UACES via the link in this record.Nonviolence has an established tradition in several disciplines,
including political theory, international relations and political
science. We explore the potential of nonviolence as analytical
and normative framework for the study of European integration
and European Union (EU) politics. At the outset, we introduce
the basics of nonviolence and define our approach to this
concept. We then apply it to three critical issues concerning the
nature of EU power, the democratic deficit and the narrative of
integration. We find that our framework re-defines the core
dimensions of the problems of power and democracy, assists in
imagining the EU in non state-morphic ways, and provides
innovative ways to put praxis at the roots of the integration
process and its narrative
Unity in fragility: Nonviolence and COVID-19
The COVID-19 pandemic witnessed extreme forms of biopolitics, as well as the urgency to reconsider our relationship with the planet. Although biopolitics draws attention to the technologies of domination by public authorities, we cast the concepts of bios and politics in the wider framework of nonviolence. In this framework, bios is the set of practices (praxis) of ordinary citizens. And politics is power created by harm reduction, or actions in daily life that testimony the desire not to harm others or the planet. We leverage nonviolence at three levels, scaling up from the individual to social behaviour and to the planet. The first level concerns nonviolence as self-sufferance and as praxis to claim back the sovereignty of the body. In the second level, nonviolence is collective mobilization - building social capital, self-governance, and solidarity. The third level provides the vision of a diverse ecological citizenship with a sustainable relationship between human beings and the planet
Polarization memory in the nonpolar magnetic ground state of multiferroic CuFeO2
We investigate polarization memory effects in single-crystal CuFeO2, which
has a magnetically-induced ferroelectric phase at low temperatures and applied
B fields between 7.5 and 13 T. Following electrical poling of the ferroelectric
phase, we find that the nonpolar collinear antiferromagnetic ground state at B
= 0 T retains a strong memory of the polarization magnitude and direction, such
that upon re-entering the ferroelectric phase a net polarization of comparable
magnitude to the initial polarization is recovered in the absence of external
bias. This memory effect is very robust: in pulsed-magnetic-field measurements,
several pulses into the ferroelectric phase with reverse bias are required to
switch the polarization direction, with significant switching only seen after
the system is driven out of the ferroelectric phase and ground state either
magnetically (by application of B > 13 T) or thermally. The memory effect is
also largely insensitive to the magnetoelastic domain composition, since no
change in the memory effect is observed for a sample driven into a
single-domain state by application of stress in the [1-10] direction. On the
basis of Monte Carlo simulations of the ground state spin configurations, we
propose that the memory effect is due to the existence of helical domain walls
within the nonpolar collinear antiferromagnetic ground state, which would
retain the helicity of the polar phase for certain magnetothermal histories.Comment: 9 pages, 7 figure
First-principles study of multiferroic RbFe(MoO)
We have investigated the magnetic structure and ferroelectricity in
RbFe(MoO) via first-principles calculations. Phenomenological analyses
have shown that ferroelectricity may arise due to both the triangular chirality
of the magnetic structure, and through coupling between the magnetic helicity
and the ferroaxial structural distortion. Indeed, it was recently proposed that
the structural distortion plays a key role in stabilising the chiral magnetic
structure itself. We have determined the relative contribution of the two
mechanisms via \emph{ab-initio} calculations. Whilst the structural axiality
does induce the magnetic helix by modulating the symmetric exchange
interactions, the electric polarization is largely due to the in-plane spin
triangular chirality, with both electronic and ionic contributions being of
relativistic origin. At the microscopic level, we interpret the polarization as
a secondary steric consequence of the inverse Dzyaloshinskii-Moriya mechanism
and accordingly explain why the ferroaxial component of the electric
polarization must be small
Evolution of magneto-orbital order upon B-site electron doping in Na1-xCaxMn7O12 quadruple perovskite manganites
We present the discovery and refinement by neutron powder diffraction of a
new magnetic phase in the Na1-xCaxMn7O12 quadruple perovskite phase diagram,
which is the incommensurate analogue of the well-known pseudo-CE phase of the
simple perovskite manganites. We demonstrate that incommensurate magnetic order
arises in quadruple perovskites due to the exchange interactions between A and
B sites. Furthermore, by constructing a simple mean field Heisenberg exchange
model that generically describes both simple and quadruple perovskite systems,
we show that this new magnetic phase unifies a picture of the interplay between
charge, magnetic and orbital ordering across a wide range of compounds.Comment: Accepted for publication in Physical Review Letter
Effect of Sr substitution on superconductivity in Hg2(Ba1-ySry)2YCu2O8-d (part2): bond valence sum approach of the hole distribution
The effects of Sr substitution on superconductivity, and more particulary the
changes induced in the hole doping mechanism, were investigated in
Hg2(Ba1-ySry)2YCu2O8-d by a "bond valence sum" analysis with Sr content from y
= 0.0 to y = 1.0. A comparison with CuBa2YCu2O7-d and Cu2Ba2YCu2O8 systems
suggests a possible explanation of the Tc enhancement from 0 K for y = 0.0 to
42 K for y = 1.0. The charge distribution among atoms of the unit cell was
determined from the refined structure, for y = 0.0 to 1.0. It shows a charge
transfer to the superconducting CuO2 plane via two doping channels pi(1) and
pi(2), i.e. through O2(apical)-Cu and Ba/Sr-O1 bonds respectively.Comment: 13 pages, 5 figures, accepted for publication in Journal of Physics:
Condensed Matte
Electrical switching of magnetic polarity in a multiferroic BiFeO3 device at room temperature
We have directly imaged reversible electrical switching of the cycloidal
rotation direction (magnetic polarity) in a (111)-BiFeO3 epitaxial-film device
at room temperature by non-resonant x-ray magnetic scattering. Consistent with
previous reports, fully relaxed (111)-BiFeO3 epitaxial films consisting of a
single ferroelectric domain were found to comprise a sub-micron-scale mosaic of
magneto-elastic domains, all sharing a common direction of the magnetic
polarity, which was found to switch reversibly upon reversal of the
ferroelectric polarization without any measurable change of the magneto-elastic
domain population. A real-space polarimetry map of our device clearly
distinguished between regions of the sample electrically addressed into the two
magnetic states with a resolution of a few tens of micron. Contrary to the
general belief that the magneto-electric coupling in BiFeO3 is weak, we find
that electrical switching has a dramatic effect on the magnetic structure, with
the magnetic moments rotating on average by 90 degrees at every cycle.Comment: 6 pages, 5 figures; corrected figure
Universal magneto-orbital ordering in the divalent -site quadruple perovskite manganites MnO ( = Ca, Sr, Cd, and Pb)
Through analysis of variable temperature neutron powder diffraction data, we
present solutions for the magnetic structures of SrMnO,
CdMnO, and PbMnO in all long-range ordered phases. The
three compounds were found to have magnetic structures analogous to that
reported for CaMnO. They all feature a higher temperature lock-in
phase with \emph{commensurate} magneto-orbital coupling, and a delocked,
multi-\textbf{k} magnetic ground state where \emph{incommensurate}
magneto-orbital coupling gives rise to a constant-moment magnetic helix with
modulated spin helicity. CdMnO represents a special case in which
the orbital modulation is commensurate with the crystal lattice and involves
stacking of fully and partially polarized orbital states. Our results provide a
robust confirmation of the phenomenological model for magneto-orbital coupling
previously presented for CaMnO. Furthermore, we show that the model
is universal to the quadruple perovskite manganites synthesised to
date, and that it is tunable by selection of the -site ionic radius
Cooling rate dependence of the antiferromagnetic domain structure of a single crystalline charge ordered manganite
The low temperature phase of single crystals of NdCaMnO
and GdCaMnO manganites is investigated by squid
magnetometry. NdCaMnO undergoes a charge-ordering
transition at =245K, and a long range CE-type antiferromagnetic state
is established at =145K. The dc-magnetization shows a cooling rate
dependence below , associated with a weak spontaneous moment. The
associated excess magnetization is related to uncompensated spins in the
CE-type antiferromagnetic structure, and to the presence in this state of
fully orbital ordered regions separated by orbital domain walls. The observed
cooling rate dependence is interpreted to be a consequence of the rearrangement
of the orbital domain state induced by the large structural changes occurring
upon cooling.Comment: REVTeX4; 7 pages, 4 figures. Revised 2001/12/0
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