Long-range order in arrays of composite and monolithic magneto-toroidal moments

Magneto-toroidal order, also called ferrotoroidicity, is the most recently established type of ferroic state. It is based on a spontaneous and uniform alignment of unit-cell-sized magnetic whirls, called magneto-toroidal moments, associated with a macroscopic toroidization. Because of its intrinsic magnetoelectric coupling, this new ferroic state could be useful in the development of spintronic devices. We exploit two-dimensional periodic arrays of magnetostatically coupled nanomagnets as model systems for the investigation of long-range magneto-toroidal order. We present two pathways promoting this order, namely (i), structures comprising a ring of uniformly magnetized sub-micrometer-sized bar magnets and (ii), structures in which each magnetic building block itself hosts a magnetic vortex. For both cases calculations of the magnetic-dipole interaction and micromagnetic simulations reveal the conditions for the formation of spontaneous magneto-toroidal order. We confirm this order and the formation of magneto-toroidal domains in our arrays by magnetic force microscopy. We identify the presence of two types of domain-wall states emerging from the competition of two intrinsic microscopic couplings. Our work not only identifies the microscopic conditions promoting spontaneous magneto-toroidal order but also highlights the possibility tailor mesoscale magnetic arrays towards elusive types of ferroic order.Comment: 20 pages, 7 figure

Magnetic diffuse scattering in artificial kagome spin ice

This is the author accepted manuscript. The final version is available from the American Physical Society via http://dx.doi.org/10.1103/PhysRevB.93.224413The study of magnetic correlations in dipolar-coupled nanomagnet systems with synchrotron x-ray scattering provides a means to uncover emergent phenomena and exotic phases, in particular in systems with thermally active magnetic moments. From the diffuse signal of soft x-ray resonant magnetic scattering, we have measured magnetic correlations in a highly dynamic artificial kagome spin ice with sub-70-nm Permalloy nanomagnets. On comparing experimental scattering patterns with Monte Carlo simulations based on a needle-dipole model, we conclude that kagome ice I phase correlations exist in our experimental system even in the presence of moment fluctuations, which is analogous to bulk spin ice and spin liquid behavior. In addition, we describe the emergence of quasi-pinch-points in the magnetic diffuse scattering in the kagome ice I phase. These quasi-pinch-points bear similarities to the fully developed pinch points with singularities of a magnetic Coulomb phase, and continually evolve into the latter on lowering the temperature. The possibility to measure magnetic diffuse scattering with soft x rays opens the way to study magnetic correlations in a variety of nanomagnetic systems.Seventh Framework Programme (Grant ID: 290605

Continuous magnetic phase transition in artificial square ice

Critical behavior is very common in many fields of science and a wide variety of many- body systems exhibit emergent critical phenomena. The beauty of critical phase transitions lies in their scale-free properties, such that the temperature dependence of physical parameters of systems differing at the microscopic scale can be described by the same generic power laws. In this work we establish the critical properties of the antiferromagnetic phase transition in artificial square ice, showing that it belongs to the two-dimensional Ising universality class, which extends the applicability of such concepts from atomistic to mesoscopic magnets. Combining soft x-ray resonant magnetic scattering experiments and Monte Carlo simulations, we characterize the transition to the low-temperature long-range order expected for the artificial square-ice system. By measuring the critical scattering, we provide direct quantitative evidence of a continuous magnetic phase transition, obtaining critical exponents which are compatible with those of the two-dimensional Ising universality class. In addition, by varying the blocking temperature relative to the phase transition temperature, we demonstrate its influence on the out-of-equilibrium dynamics due to critical slowing down at the phase transition

Imaging of Domain Wall Inertia in Permalloy Half-Ring Nanowires by Time-Resolved Photoemission Electron Microscopy

Using photoemission electron microscopy, we image the dynamics of a field pulse excited domain wall in a Permalloy nanowire. We find a delay in the onset of the wall motion with respect to the excitation and an oscillatory relaxation of the domain wall back to its equilibrium position, defined by an external magnetic field. The origin of both of these inertia effects is the transfer of energy between energy reservoirs. By imaging the distribution of the exchange energy in the wall spin structure, we determine these reservoirs, which are the basis of the domain wall mass concept

Review of accident and emergency, trauma and orthopaedic services in Leeds

SIGLEAvailable from British Library Document Supply Centre- DSC:GPC/07431 / BLDSC - British Library Document Supply CentreGBUnited Kingdo

Mathematik in der Grundschule Erweiterung des Zahlenraumes von 10 bis 1000000

Available from FIZ Karlsruhe / FIZ - Fachinformationszzentrum Karlsruhe / TIB - Technische InformationsbibliothekSIGLEDEGerman

Direct observation of high velocity current induced domain wall motion

We study fast vortex wall propagation in Permalloy wires induced by 3 ns short current pulses with sub 100 ps rise time using high resolution magnetic imaging at zero field.We find a constant domain wall displacement after each current pulse as well as current induced domain wall structure changes, even at these very short timescales. The domain wall velocities are found to be above 100 m/s and independent of the domain wall spin structure. Comparison to experiments with longer pulses points to the pulse shape as the origin of the high velocities

Selective domain wall depinning by localized Oersted fields and Joule heating

Using low temperature magnetoresistance measurements, the possibility to selectively move a domain wall locally by applying current pulses through a Au nanowire adjacent to a permalloy element is studied. We find that the domain wall depinning field is drastically modified with increasing current density due to the Joule heating and the Oersted field of the current, and controlled motion due to the Oersted field without any externally applied fields is achieved. By placing the domain wall at various distances from the Au wire, we determine the range of the Joule heating and the Oersted field and both effects can be separated