Easy-axis Structure Research Articles

Large topological Hall effect in an easy-cone ferromagnet (Cr0.9B0.1)Te

The Berry phase understanding of electronic properties has attracted special interest in condensed matter physics, leading to phenomena such as the anomalous Hall effect and the topological Hall effect. A non-vanishing Berry phase, induced in momentum space by the band structure or in real space by a non-coplanar spin structure, is the origin of both effects. Here, we report a sign conversion of the anomalous Hall effect and a large topological Hall effect in (Cr0.9B0.1)Te single crystals. The spin reorientation from an easy-axis structure at high temperature to an easy-cone structure below 140 K leads to conversion of the Berry curvature, which influences both, anomalous and topological, Hall effects in the presence of an applied magnetic field and current. We compare and summarize the topological Hall effect in four categories with different mechanisms and have a discussion into the possible artificial fake effect of the topological Hall effect in polycrystalline samples, which provides a deep understanding of the relation between the spin structure and Hall properties.

Fe-based alloy laminated films with crossing easy axis structure and their applications to laminated film heads for high-frequency use

To realize laminated film heads with superior recording and reproducing capability in high frequency region, we have investigated Fe-based alloy (Bs=1.6 T) laminated films with different laminating structures: one with magnetostatically coupled laminated films and the other with laminated films having crossing easy axis structure. Although the magnetostatically coupled Fe-based laminated films show high initial permeability even in a narrow shape area near the magnetic gap, they have anisotropic initial permeability, and therefore the laminated film head using this film shows lower playback output compared with conventional Go-based amorphous film head below 20 MHz. The Fe-based laminated film with crossing easy axis structure with 5 nm SiO2 shows isotropically high initial permeability in high frequency region and maintains high initial permeability even in a narrow shape area near the magnetic gap. Consequently, the laminated film head using this film shows excellent recording and reproducing characteristics for metal particle tape (MP-tape) for wide frequency ranges.

Magneto-impedance and ΔE measurements of iron- and cobalt-based amorphous wires

Magneto-impedance and /spl Delta/E measurements of amorphous wires having the compositions Fe/sub 77.5/Si/sub 10/B/sub 15/ and Co/sub 72.5/Si/sub 12.5/B/sub 15/ in the as-quenched and annealed states are presented. The results are interpreted in the light of the widely accepted core-shell domain models for positively and negatively magnetostrictive amorphous wires respectively. It is concluded that in wires of Fe/sub 7.5/Si/sub 10/B/sub 15/ the radial easy axis structure in the shell of the as-quenched wire weakens after light annealing, eventually giving way to a circumferential structure when surface crystallization occurs. In wires of Co/sub 72.5/Si/sub 12.5/B/sub 15/ significant circumferential anisotropy is inferred in all states of annealing studied.

Magnetic phase diagrams and helical magnetic phases in MxNi 1−xBr 2 ( M =Fe, Mn): A neutron diffraction and magneto-optical study

Below T N = 44K, NiBr 2 orders as an easy-plane antiferromagnet, but at T IC ∼ 23K it undergoes a transition to a helimagnetic phase whose propagation vector, τ, increases smoothly to a limiting value [0.027,0.027,0] at 4.2 K. The magnetic order in NiBr 2 and M x Ni 1−xBr 2 ( M =Fe, Mn) is investigated by single-crystal neutron diffraction. In Fe x Ni 1− x Br 2 τ changes from the [110] to [100] direction at 3.7(17)% Fe. Its magnitude, and T IC, remain constant up to 9.9(14)% Fe, but above this concentration a collinear, easy-axis structure is stable at all temperatures below T N, which decreases towards the value of 11 K in FeBr 2. Doping 2.9% Mn 2+ into NiBr 2 decreases T IC slightly, in the manner previously observed for diamagnetic dopants. Refinement of powder X-ray diffraction profiles show the lattice distortions in the doped materials to be small, while the structures of some Fe x Ni 1− x Br 2 samples are confirmed by refinement of the powder neutron diffraction profiles. The temperature and field dependence of hot and cold exciton-magnon combination bands in the optical absorption spectra of Fe 2+- and Mn 2+-doped crystals give additional information about magnetic order. The magnetic behaviour is interpreted in terms of perturbations of the exchange constants J 1,2,3, and J′ and the anisotropy constant D.

Multilayer processing for magnetic film memory devices

Planar processing techniques for producing coupled film storage devices are presented. The discussion centers around a process sequence for a coupled easy-axis structure built on a metal substrate, largely by vacuum deposition techniques. The process results in packing density of about 8000 bits/in2. Included is a test of one such element displaying useful memory device characteristics under conditions of a worst case pulse test program.