Generation of single skyrmions by picosecond magnetic field pulses

We numerically demonstrate an ultrafast method to create $\textit{single}$ skyrmions in a $\textit{collinear}$ ferromagnetic sample by applying a picosecond (effective) magnetic field pulse in the presence of Dzyaloshinskii-Moriya interaction. For small samples the applied magnetic field pulse could be either spatially uniform or nonuniform while for large samples a nonuniform and localized field is more effective. We examine the phase diagram of pulse width and amplitude for the nucleation. Our finding could ultimately be used to design future skyrmion-based devices.Comment: 4.5 pages+Supplemental Materia

Arrays of elliptical Fe(001) nanoparticles : Magnetization reversal, dipolar interactions, and effects of finite array sizes

The magnetic properties of arrays of nanoparticles are determined by the interplay between the individual particle properties and the dipolar interactions between them. Here we present a study of arrays of elliptical Fe(001) particles of thickness 10-50 nm. The aspect ratios of the ellipses are 1:3, their short axes a = 50, 100, or 150 nm, and the periodicity of the rectangular arrays is either two or four times the corresponding axes of the ellipses. Magnetic measurements together with numerical and micromagnetic calculations yield a consistent picture of the arrays, comprising single-domain nanoparticles. We show that the magnetization reversal, occurring in the range 100-400 mT for fields applied along the long axis, is mainly determined by the properties of the corresponding single Fe ellipses. The interaction fields of the order of tens of mT can be tuned by the array configurations. For the actual arrays the interactions promote switching. For film thicknesses below the Bloch wall width parameter of Fe, l(w) = 22 nm, magnetization reversal occurs without formation of domain walls or vortices. Within this range arrays may be tuned to obtain a well-defined switching field. Two general conclusions are drawn from the calculations: the character of the interaction, whether it promotes or delays magnetization reversal, is determined by the aspect ratio of the array grid, and the interaction strength saturates as the size of the array increases

Разработка 2D игры "Три в ряд" на платформе Unity под OC Android

The magnetic properties of arrays of nanoparticles are determined by the interplay between the individual particle properties and the dipolar interactions between them. Here we present a study of arrays of elliptical Fe(001) particles of thickness 10-50 nm. The aspect ratios of the ellipses are 1:3, their short axes a = 50, 100, or 150 nm, and the periodicity of the rectangular arrays is either two or four times the corresponding axes of the ellipses. Magnetic measurements together with numerical and micromagnetic calculations yield a consistent picture of the arrays, comprising single-domain nanoparticles. We show that the magnetization reversal, occurring in the range 100-400 mT for fields applied along the long axis, is mainly determined by the properties of the corresponding single Fe ellipses. The interaction fields of the order of tens of mT can be tuned by the array configurations. For the actual arrays the interactions promote switching. For film thicknesses below the Bloch wall width parameter of Fe, l(w) = 22 nm, magnetization reversal occurs without formation of domain walls or vortices. Within this range arrays may be tuned to obtain a well-defined switching field. Two general conclusions are drawn from the calculations: the character of the interaction, whether it promotes or delays magnetization reversal, is determined by the aspect ratio of the array grid, and the interaction strength saturates as the size of the array increases

Polyploidy and habitat differentiation in Deschampsia cespitosa

The chromosome numbers of 114 populations of the Deschampsia cespitosa (L.) Beauv. complex, widely distributed in the British Isles, were determined from root-tip squash preparations. This revealed two widespread morphologically cryptic chromosomal races of seminiferous D. cespitosa (2n= 26, 52). The tetraploid is found throughout Britain; its range of habitats includes meadows, pastures, woodland, plantations, verges and waste ground. This is the first report of an extensive geographical distribution for tetraploid seminiferous D. cespitosa. The diploid appears to be mainly restricted to woodland, of mostly ancient, semi-natural origin. Populations with both chromosome numbers are rare. The tetraploid is usually found where invasive colonization has clearly occurred. The closely related proliferous taxon, D. alpina (L.) Roem. & Schult., was tetraploid, in agreement with published data. The prolifery itself induces changes in floret morphology. The floral morphology and cytological data together suggest that sub-specific rank is appropriate for this variant in British material