830 research outputs found
Phenomenology of chiral damping in noncentrosymmetric magnets
A phenomenology of magnetic chiral damping is proposed in the context of
magnetic materials lacking inversion symmetry breaking. We show that the
magnetic damping tensor adopts a general form that accounts for a component
linear in magnetization gradient in the form of Lifshitz invariants. We propose
different microscopic mechanisms that can produce such a damping in
ferromagnetic metals, among which spin pumping in the presence of anomalous
Hall effect and an effective "-" Dzyaloshinskii-Moriya antisymmetric
exchange. The implication of this chiral damping in terms of domain wall motion
is investigated in the flow and creep regimes. These predictions have major
importance in the context of field- and current-driven texture motion in
noncentrosymmetric (ferro-, ferri-, antiferro-)magnets, not limited to metals.Comment: 5 pages, 2 figure
Urban growth, regeneration and social inclusion in Porto Alegre: the City Entrance Integrated Programme case study
Since 1989 Porto Alegre has become an international reference for planning (UN Habitat, 1996) and regeneration practices associated also with the Participatory Budget process (Pacheco, 2001; Fedozzi, 1998), aiming at poverty reduction and social inclusiveness (Getúlio Vargas Foundation, 2004; UNDP, 2003; UN/UMP, 2003). Within the new city masterplan approved in 1999 the City Entrance Integrated Programme (henceforth PIEC) has been delivered since 2002 (Vargas, 2003; PMPA, 2014). The paper critically analyses the outcomes of the 4th District’s regeneration process and relate them to recent trends in terms of informal rapid urbanisation, social and ecological indicators.
The findings highlight how, even though enjoying economic development and positive macro-economic trends, Porto Alegre is facing new or increasing challenges in terms of housing needs, informal urbanisation, social and environmental resilience. Unexpected internal people displacement, together with real estate speculation and the rise of new informal urbanization, provide a worrying picture of increasing inequalities across the city. The paper provides a reflection on the shortcomings and the fragility of the planning process, especially in terms of social and environmental impact, to draw some provisional conclusions and directions for further research activities
Current induced domain wall dynamics in the presence of spin orbit torques
Current induced domain wall (DW) motion in perpendicularly magnetized
nanostripes in the presence of spin orbit torques is studied. We show using
micromagnetic simulations that the direction of the current induced DW motion
and the associated DW velocity depend on the relative values of the field like
torque (FLT) and the Slonczewski like torques (SLT). The results are well
explained by a collective coordinate model which is used to draw a phase
diagram of the DW dynamics as a function of the FLT and the SLT. We show that a
large increase in the DW velocity can be reached by a proper tuning of both
torques.Comment: 9 pages, 3 figure
Al-Substitution Effects on Physical Properties of the Colossal Magnetoresistance Compouns La0.67ca0.33mno3
We present a detailed study of the polycrystalline perovskite manganites
La0.67Ca0.33AlxMn1-xO3 (x = 0, 0.1, 0.15, 0.5) at low temperatures and high
magnetic fields, including electrical resistance, magnetization, ac
susceptibility. The static magnetic susceptibility was also measured up to 1000
K. All the samples show colossal magnetoresistance behavior and the Curie
temperatures decrease with Al doping. The data suggest the presence of
correlated magnetic clusters near by the ferromagnetic transition. This appears
to be a consequence of the structural and magnetic disorder created by the
random distribution of Al atoms.Comment: 13 pages including 5 figure
Fedosov Quantization of Lagrange-Finsler and Hamilton-Cartan Spaces and Einstein Gravity Lifts on (Co) Tangent Bundles
We provide a method of converting Lagrange and Finsler spaces and their
Legendre transforms to Hamilton and Cartan spaces into almost Kaehler
structures on tangent and cotangent bundles. In particular cases, the Hamilton
spaces contain nonholonomic lifts of (pseudo) Riemannian / Einstein metrics on
effective phase spaces. This allows us to define the corresponding Fedosov
operators and develop deformation quantization schemes for nonlinear mechanical
and gravity models on Lagrange- and Hamilton-Fedosov manifolds.Comment: latex2e, 11pt, 35 pages, v3, accepted to J. Math. Phys. (2009
High domain wall velocities induced by current in ultrathin Pt/Co/AlOx wires with perpendicular magnetic anisotropy
Current-induced domain wall (DW) displacements in an array of ultrathin
Pt/Co/AlOx wires with perpendicular magnetic anisotropy have been directly
observed by wide field Kerr microscopy. DWs in all wires in the array were
driven simultaneously and their displacement on the micrometer-scale was
controlled by the current pulse amplitude and duration. At the lower current
densities where DW displacements were observed (j less than or equal to 1.5 x
10^12 A/m^2), the DW motion obeys a creep law. At higher current density (j =
1.8 x 10^12 A/m^2), zero-field average DW velocities up to 130 +/- 10 m/s were
recorded.Comment: Minor changes to Fig. 1(b) and text, correcting for the fact that
domain walls were subsequently found to move counter to the electron flow.
References update
Domain wall tilting in the presence of the Dzyaloshinskii-Moriya interaction in out-of-plane magnetized magnetic nanotracks
We show that the Dzyaloshinskii-Moriya interaction (DMI) can lead to a
tilting of the domain wall (DW) surface in perpendicularly magnetized magnetic
nanotracks when DW dynamics is driven by an easy axis magnetic field or a spin
polarized current. The DW tilting affects the DW dynamics for large DMI and the
tilting relaxation time can be very large as it scales with the square of the
track width. The results are well explained by an analytical model based on a
Lagrangian approach where the DMI and the DW tilting are included. We propose a
simple way to estimate the DMI in a magnetic multilayers by measuring the
dependence of the DW tilt angle on a transverse static magnetic field. Our
results shed light on the current induced DW tilting observed recently in Co/Ni
multilayers with inversion asymmetry, and further support the presence of DMI
in these systems.Comment: 12 pages, 3 figures, 1 Supplementary Material
Electric-field control of domain wall nucleation and pinning in a metallic ferromagnet
The electric (E) field control of magnetic properties opens the prospects of
an alternative to magnetic field or electric current activation to control
magnetization. Multilayers with perpendicular magnetic anisotropy (PMA) have
proven to be particularly sensitive to the influence of an E-field due to the
interfacial origin of their anisotropy. In these systems, E-field effects have
been recently applied to assist magnetization switching and control domain wall
(DW) velocity. Here we report on two new applications of the E-field in a
similar material : controlling DW nucleation and stopping DW propagation at the
edge of the electrode
Magnetic domain wall motion in a nanowire: depinning and creep
The domain wall motion in a magnetic nanowire is examined theoretically in
the regime where the domain wall driving force is weak and its competition
against disorders is assisted by thermal agitations. Two types of driving
forces are considered; magnetic field and current. While the field induces the
domain wall motion through the Zeeman energy, the current induces the domain
wall motion by generating the spin transfer torque, of which effects in this
regime remain controversial. The spin transfer torque has two mutually
orthogonal vector components, the adiabatic spin transfer torque and the
nonadiabatic spin transfer torque. We investigate separate effects of the two
components on the domain wall depinning rate in one-dimensional systems and on
the domain wall creep velocity in two-dimensional systems, both below the
Walker breakdown threshold. In addition to the leading order contribution
coming from the field and/or the nonadiabatic spin transfer torque, we find
that the adiabatic spin transfer torque generates corrections, which can be of
relevance for an unambiguous analysis of experimental results. For instance, it
is demonstrated that the neglect of the corrections in experimental analysis
may lead to incorrect evaluation of the nonadiabaticity parameter. Effects of
the Rashba spin-orbit coupling on the domain wall motion are also analyzed.Comment: 14 pages, 3 figure
- …