The technological appeal of multiferroics is the ability to control magnetism with electric field. For devices to be useful, such control must be achieved at room temperature. The only single-phase multiferroic material exhibiting unambiguous magnetoelectric coupling at room temperature is BiFeO3 (refs 4 and 5). Its weak ferromagnetism arises from the canting of the antiferromagnetically aligned spins by the Dzyaloshinskii-Moriya (DM) interaction. Prior theory considered the symmetry of the thermodynamic ground state and concluded that direct 180-degree switching of the DM vector by the ferroelectric polarization was forbidden. Instead, we examined the kinetics of the switching process, something not considered previously in theoretical work. Here we show a deterministic reversal of the DM vector and canted moment using an electric field at room temperature. First-principles calculations reveal that the switching kinetics favours a two-step switching process. In each step the DM vector and polarization are coupled and 180-degree deterministic switching of magnetization hence becomes possible, in agreement with experimental observation. We exploit this switching to demonstrate energy-efficient control of a spin-valve device at room temperature. The energy per unit area required is approximately an order of magnitude less than that needed for spin-transfer torque switching. Given that the DM interaction is fundamental to single-phase multiferroics and magnetoelectrics, our results suggest ways to engineer magnetoelectric switching and tailor technologically pertinent functionality for nanometre-scale, low-energy-consumption, non-volatile magnetoelectronics.

We use spin-transfer-driven ferromagnetic resonance (ST-FMR) to measure the spintransfer torque vector τ in MgO-based magnetic tunnel junctions as a function of the offset angle between the magnetic moments of the electrodes and as a function of bias, V.We explain the conflicting conclusions of two previous experiments by accounting for additional terms that contribute to the ST-FMR signal at large |V|. Including the additional terms gives us improved precision in the determination of τ(V), allowing us to distinguish among competing predictions. We determine that the in-plane component of dτ /dV has a weak but non-zero dependence on bias, varying by 30-35% over the bias range where the measurements are accurate, and that the perpendicular component can be large enough to be technologically significant. We also make comparisons to other experimental techniques that have been used to try to measure τ(V). : 76.50.+g, 72.25.-b, 85.75.-d PACS

Aims. We study polarized short-wavelength emission from the inner Galaxy, which is nearly invisible at long wavelengths because of depolarization. We attempt to obtain information on the diffuse continuum emission at short wavelengths to help us to separate Galactic thermal and non-thermal components. Methods. We conducted a total intensity and polarization survey of the Galactic plane at λ6 cm using the Urumqi 25 m telescope for the Galactic longitude range of 10 • ≤ l ≤ 60 • and the Galactic latitude range of |b| ≤ 5 • . Missing absolute zero levels of Stokes U and Q maps were restored by extrapolating the WMAP five-year K-band polarization data. For total intensities, we recovered missing large-scale components by referring to the Effelsberg λ11 cm survey. Results. Total intensity and polarization maps are presented with an angular resolution of 9. 5 and a sensitivity of 1 mK T B and 0.5 mK T B in total and polarized intensity, respectively. The λ6 cm polarized emission in the Galactic plane originates within about 4 kpc distance, which increases for polarized emission out of the plane. The polarization map shows "patches", "canals", and "voids" with no correspondence in total intensity. We attribute the patches to turbulent magnetic field cells. Canals are caused by abrupt variation in the polarization angles at the boundaries of patches rather than by foreground Faraday screens. The superimposition of foreground and Faraday screen rotated background emission almost cancels the polarized emission locally, such that polarization voids appear. By modelling the voids, we estimate the Faraday screen's regular magnetic field along the line-of-sight to be larger than about 8 μG. We separated thermal (free-free) and non-thermal (synchrotron) emission according to their different spectral indices. The spectral index for the synchrotron emission is based on WMAP polarization data. The fraction of thermal emission at λ6 cm is about 60% in the plane. Conclusions. The Sino-German λ6 cm polarization survey of the inner Galaxy provides new insights into the properties of the magnetized interstellar medium for this very complex Galactic region, which is Faraday thin up to about 4 kpc in the Galactic plane. Within this distance polarized patches are identified as intrinsic structures related to turbulent Galactic magnetic fields of spatial scales from 20(d/4 kpc) to 200(d/4 kpc) pc.

We report single-shot measurements of resistance versus time for thermally assisted spintorque-driven switching in magnetic tunnel junctions. We achieve sufficient sensitivity to resolve the resistance signals leading up to switching, including the variations between individual switching events. Analyses of pre-switching thermal fluctuations allow detailed measurements of coherence times and variations in magnetization precession amplitude. We find that with a small in-plane hard-axis magnetic field the magnetization dynamics are more spatially coherent than for the case of zero field. Page 2 of 13Magnetization switching induced by spin transfer torque [1,2] is of interest both for probing the fundamental physics of magnetic dynamics and for applications in storage technologies [3,4]. Measurements in the time domain [5][6][7][8][9][10][11] can provide the most direct information about spin-torque-driven magnetic dynamics. However, most previous timeresolved studies [5][6][7][8][9] employed stroboscopic approaches, which average over many events so that they reveal only average behavior and hide individual variations. Magnetic tunnel junctions (MTJs) can now provide sufficiently large resistance signals (relative to metal spin valves [5][6][7][8]) for single-shot measurements. Two initial experiments have measured distributions of spin-torque switching times in MTJs using single-shot techniques [10,11] but they did not resolve the dynamics leading to switching. Here we report single-shot measurements of spin-torque switching in MTJs with sufficiently improved sensitivity to study the pre-switching resistance signals in detail. We observe the variations between switching processes caused by thermal fluctuations and can perform comprehensive analyses of the fluctuations prior to switching. We find that switching is more spatially coherent when the magnetic moments of the electrodes are initially offset (at an angle different than 0º or 180º) than when the moments are collinear.The MTJ samples that we study have the layer structure (in nm): bottom contact . Our discussion of currentdriven reversal will focus on switching from the anti-parallel (AP) state to parallel (P) state because this required approximately 30% lower voltages than P-to-AP switching.Page 3 of 13However, measurements of P-to-AP dynamics are qualitatively similar. We will examine switching both in the case of zero total field on the free layer (in which an applied field cancels H d ) and the case that a small (100 Oe) field is applied along the in-plane hard axis, to rotate the free-layer magnetization approximately 15º from the strictly AP configuration (see inset, Fig. 1(a)). We will present data from a single sample, but have studied two other devices in zero field and one other in the hard-axis field, with all showing the same differences depending on field geometry.We perform single-shot measurements using the circuit shown in Fig. 1(b). After initializing the sample in the AP state we use a pulse generator to produce an 100 ns long, 300 ps ri...

We consider the curvature emission properties from relativistic particles streaming along magnetic field lines and corotating with pulsar magnetosphere. The corotation affects the trajectories of the particles and hence the emission properties, especially the polarization. We consider the modification of the particle velocity and acceleration due to the corotation. Curvature radiation from a single particle is calculated using the approximation of a circular path to the particle trajectory. Curvature radiation from particles at a given height actually contains the contributions from particles streaming along all the nearby field lines around the tangential point, forming the emission cone of 1/γ. The polarization patterns of the emission cone are distorted by the additional rotation, which is more serious for emission from a larger height. Net circular polarization can be generated by the density gradient in the emission cone. For three typical density models in the form of core, cone and patches, we calculate the polarization profiles for emission generated at a given height. We find that the circular polarization could have a single sign or sign reversal, depending on the density gradient along the rotation phase. The polarization profiles of the total curvature radiation from the whole open field line region, calculated by adding the emission from all possible heights, are similar to that from a dominating emission height. The circular polarization of curvature radiation has sign reversals in the emission from density patches, while it has a single sign for the emission from density core and is negligible for the emission from density cone.