Domain Nucleation and Annihilation in Uniformly Magnetized State under Current Pulses in Narrow Ferromagnetic Wires

We investigate the current-driven magnetization dynamics in narrow Permalloy wires by means of Lorentz microscopy and electron holography. Current pulses are found to transform the magnetic structure in the uniformly magnetized state below the Curie temperature. A variety of magnetic states including reversed magnetic domains are randomly obtained in low probability. The dynamics of vortices found in most of observed magnetic states seems to play a key role in triggering the magnetization reversal.Comment: 11 pages, 3 figures, 1 video, to appear in Japanese Journal of Applied Physics (Express Letter

Incommensurate--commensurate transitions in the mono-axial chiral helimagnet driven by the magnetic field

The zero temperature phase diagram of the mono-axial chiral helimagnet in the magnetic field plane formed by the components parallel and perpendicular to the helical axis is thoroughly analyzed. The nature of the transition to the commensurate state depends on the angle between the field and the helical axis. For field directions close to the directions parallel or perpendicular to the helical axis the transition is continuous, while for intermediate angles the transition is discontinuous and the incommensurate and commensurate states coexist on the transition line. The continuous and discontinuous transition lines are separated by two tricritical points with specific singular behaviour. The location of the continuous and discontinuous lines and of the tricritical points depend strongly on the easy-plane anisotropy, the effect of which is analyzed. For large anisotropy the conical approximation locates the transition line very accurately, although it does not predict the continuous transitions nor the tricitical behaviour. It is shown that for large anisotropy, as in CrNb3S6, the form of the transition line is universal, that is, independent of the sample, and obeys a simple equation. The position of the tricritical points, which is not universal, is theoretically estimated for a sample of CrNb3S6Comment: 10 pages, 9 figure

Spin polarization gate device based on the chirality-induced spin selectivity and robust nonlocal spin polarization

Nonlocal spin polarization phenomena are thoroughly investigated in the devices made of chiral metallic single crystals of CrNb$_3$S$_6$ and NbSi$_2$ as well as of polycrystalline NbSi$_2$. We demonstrate that simultaneous injection of charge currents in the opposite ends of the device with the nonlocal setup induces the switching behavior of spin polarization in a controllable manner. Such a nonlocal spin polarization appears regardless of the difference in the materials and device dimensions, implying that the current injection in the nonlocal configuration splits spin-dependent chemical potentials throughout the chiral crystal even though the current is injected into only a part of the crystal. We show that the proposed model of the spin dependent chemical potentials explains the experimental data successfully. The nonlocal double-injection device may offer significant potential to control the spin polarization to large areas because of the nature of long-range nonlocal spin polarization in chiral materials.Comment: 8 pages, 8 figure

Chirality-selected crystal growth and spin polarization over centimeters of transition metal disilicide crystals

We performed a chirality-controlled crystal growth of transition metal disilicide NbSi$_{2}$ and TaSi$_{2}$ by using a laser-diode-heated floating zone (LDFZ) method. The crystal chirality was evaluated in the crystals of centimeters in length by performing single crystal X-ray diffraction as well as probing a spin polarization originating from chirality-induced spin selectivity (CISS) effect. The crystals of right-handed NbSi$_{2}$ and of left-handed TaSi$_{2}$ were obtained in the conventional LDFZ crystal growth, while the left-handed NbSi$_{2}$ and right-handed TaSi$_{2}$ crystals were grown by the LDFZ method with the composition-gradient feed rods. The spin polarization via the CISS was observed over centimeters in the NbSi$_{2}$ single crystals and the sign of the CISS signals was dependent on the chirality of crystals. The correlation between the crystal chirality and CISS signals indicates that the CISS measurements work as a non-destructive method for chirality determination even in centimeter-long specimens.Comment: 9 pages, 6 figure