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Magnetic structure factor (MSF), calculated from ground state configuration previously obtained by Monte Carlo simulation in different rectangular artificial spin ices, is employed to investigate ground state degeneracy. Our analysis considers the importance of nanoislands size to the ratio between rectangle sides in the lattice parameters via a dumbbell model. Pinch points in MSF along with residual entropy, determined for a number of different rectangular lattices with disconnected nanoislands, point out the conditions for the emergency of a gauge field, through which magnetic monopoles interact effectively. [ABSTRACT FROM AUTHOR]

Ultra-thin layers (< 8 nm) of a Bi 2 Te 3 topological insulator have been grown on GaAs (100) substrates using molecular beam epitaxy. The growth was performed from a single Bi 2 Te 3 effusion cell and one source of extra tellurium. Optical and structural characterizations were carried out through Raman spectroscopy, x-ray diffraction, atomic force microscopy, and scanning electron microscopy. The topological insulator properties were also investigated by angle-resolved photoelectron spectroscopy. A layer of 5 nm showed Dirac cone-like linear electronic band dispersion, indicating the signature of a topological insulator with the Dirac point having large binding energy relative to the Fermi level as expected for ultra-thin films. Topological insulator properties were also investigated at the initial growth stage where deposition follows an islandlike growth mode. Our results can contribute to the development of practical chalcogenide-based thin-film spintronics devices. [ABSTRACT FROM AUTHOR]

Magnetic monopole motion (without its partner in a pair) as a function of external magnetic fields is presented as a fingerprint of freedom of these emergent quasi-particles in a two-dimensional artificial spin ice material. Such freedom, required, for example, for further application in magnetricity, is only possible due to ground-state degeneracy, which causes an anisotropic string energy reduction in rectangular ice geometries, designed to allow highest equidistance among lateral and diagonal neighbor nanomagnets. By measurements of magnetic force microscopy, we observe magnetic monopole creation, transport, and annihilation in such an arrangement, where monopoles are free to move throughout large regions of the sample, since they are not permanently bound by the string bonds, as commonly observed in conventional artificial spin ice systems. Instead, monopoles leave a wake of elongated tensionless string, which is connected to superficial charges or charges pinned to the array borders. [ABSTRACT FROM AUTHOR]

Micromagnetic simulations have been performed to investigate the controllability of the skyrmion position in antiferromagnetic nanotracks with their magnetic properties modified spatially. In this study, we have modeled magnetic defects as local variations on the material parameters, such as the exchange stiffness, saturation magnetization, perpendicular magnetocrystalline anisotropy, and Dzyaloshinskii–Moriya constant. Thus, we have observed not only pinning (potential well) but also scattering (potential barrier) of antiferromagnetic skyrmions, when adjusting either a local increase or a local reduction for each material parameter. In order to control the skyrmion motion, it is very important to impose certain positions along the nanotrack where the skyrmion can stop. Magnetic defects incorporated intentionally in antiferromagnetic racetracks can be useful for such a purpose. In order to provide guidelines for experimental studies, we vary both material parameters and the size of the modified region. The results obtained show that the efficiency of skyrmion traps depends on a suitable combination of magnetic defect parameters. Furthermore, we discuss the reason why skyrmions are either attracted or repelled by a region magnetically modified. [ABSTRACT FROM AUTHOR]

In this work, we perform investigations of the competition between domain-wall pinning and attraction by antinotches and finite device borders. The conditions for optimal geometries, which can attain a stable domain-wall pinning, are presented. This allows the proposition of a three-terminal device based on domain-wall pinning. We obtain, with very small pulses of current applied parallel to the nanotrack, a fast motion of the domain-wall between antinotches. In addition to this, a swift stabilization of the pinned domain-wall is observed with a high percentage of orthogonal magnetization, enabling high magnetoresistive signal measurements. Thus, our proposed device is a promising magnetoresistive random access memory device with good scalability, duration, and high speed information storage. [ABSTRACT FROM AUTHOR]

Sets of nanomagnets are often utilized to mimic cellular automata in the design of nanomagnetic logic devices or frustration and emergence of magnetic monopoles in artificial spin ice systems, once that unidirectional arrangement of nanomagnets can behave as artificial spin ice, with frustration arising from second neighbors' dipolar interaction, and present good magnetic monopole mobility due to the low string tension among charges. Here, we present an experimental investigation of magnetic monopole population and mobility as a function of lateral and longitudinal distance among nanomagnets. The observed results could be useful in the nanomagnet logic device design and bring new insights about several possible designs for tuning magnetic monopole unidirectional mobility and transport under a low external magnetic field for further application in magnetricity. [ABSTRACT FROM AUTHOR]

Various spintronic devices use single-domain magnetic nanoparticles as unit cells. Herein, we investigated interparticle dipole-dipole interactions in arrays of Permalloy single-domain nano-ellipses through micromagnetic simulations. In this study, the variation is introduced not only to the aspect ratio and the spacing between ellipses but to the magnetization distribution and the 2D lattice type as well. When integrating the Landau-Lifshitz-Gilbert equation with zero external magnetic field, equilibrium magnetic configurations were obtained for each array. For small values of the spacing between ellipses, they interact strongly, such that the shape anisotropy is locally modified by the distribution of the magnetization. Moreover, the effect of the dipolar coupling on the precessional magnetization reversal is also studied. The minimum field strength required to switch the magnetization depends on the magnetization distribution in a strongly interacting magnetic system. Consequently, we have assessed the minimum spacing between particles in which single-domain nano-ellipses becomes a non-interacting magnetic system. [ABSTRACT FROM AUTHOR]

We have studied ferromagnetic nickel thin films patterned with square lattices of elongated antidots that are negative analogues of square artificial spin ice. Micromagnetic simulations and direct current magnetic moment measurements reveal in-plane anisotropy of the magnetic hysteresis loops, and the formation of a dense array of magnetic vortices with random polarization and chirality. These multiply-connected antidot arrays could be superior to lattices of disconnected nanodisks for investigations of vortex switching by applied electric current. [ABSTRACT FROM AUTHOR]

We design a semigranular system consisting of permalloy clusters electrodeposited on silicon substrates that permits us to transfer and polarize spin of practically unpolarized currents injected between Ohmic contacts on silicon. The experiments are done for different times of electrodeposition and the magnetoresistance signal is measured. We realize a method to coherently couple, through currents, properties of individual clusters. [ABSTRACT FROM AUTHOR]

We investigated a permeable metal base transistor consisting of a ZnO/NiFe/Si heterostructure. Both ZnO and NiFe layers were grown by electrodeposition techniques, using only adhesive tape masks to define deposition regions. The base permeability can thus be controlled by varying the NiFe deposition time. We report here our best results obtained for the permeable NiFe base close to the electrical percolation threshold, which gives reasonable sensitivity to the device. Magnetocurrent measurements carried out at room temperature show that this permeable metal base transistor is stable and sensitive under applied magnetic fields of low intensities, ∼ 100 Oe, required for electronics integration. [ABSTRACT FROM AUTHOR]

We report the spin-to-charge current conversion in an intrinsic topological insulator (TI) (Bi0.22Sb0.78)2Te3 film at room temperature. The spin currents are generated in a thin layer of permalloy (Py) by two different processes, the spin pumping effect (SPE) and the spin Seebeck effect (SSE). In the first, we use microwave-driven ferromagnetic resonance of the Py film to generate a SPE spin current that is injected into the TI (Bi0.22Sb0.78)2Te3 layer in direct contact with Py. In the second, we use the SSE in the longitudinal configuration in Py without contamination by the anomalous Nernst effect, which was made possible with a thin NiO layer between the Py and (Bi0.22Sb0.78)2Te3 layers. The spin-to-charge current conversion is dominated by the TI surface states and is attributed to the inverse Edelstein effect (IEE), which is made possible by the spin-momentum locking in the electron Fermi contours due to the Rashba field. The measurements by the two techniques yield very similar values for the IEE parameter, which are larger than the reported values in the previous studies on topological insulators. [ABSTRACT FROM AUTHOR]