Quantum State of Neutrons in Magnetic Thin Films and Superlattices

An experiment which describes the quantum states of neutrons in magnetic thin films and superlattices is reviewed.Comment: 3 pages, 3 figures, Neutron New

Vortex states in patterned exchange biased NiO/Ni samples

We investigated the magnetization reversal of arrays of exchange biased NiO/Ni squares with superconducting quantum interference device magnetometry and micromagnetic simulations. The edges of the squares were 0.5, 1.5, and 3.0 $\mu$m long. The NiO/Ni structures exhibit vortexlike hysteresis loops and micromagnetic calculations show that this feature is due to several vortices nucleating in the islands. Furthermore, for the arrays with squares of 1.5 $\mu$m edge length, the sign of the exchange bias field changes, as compared to the same continuous NiO/Ni layer. We attribute the vortex nucleation and the change of the exchange bias field to the interplay between shape and unidirectional anisotropy.Comment: 6 pages, 7 figure

Six-fold in-plane magnetic anisotropy in Co-implanted ZnO (0001)

Magnetic anisotropies of Co-implanted ZnO (0001) films grown on single-crystalline Al2O3 (11-20) substrates have been studied by ferromagnetic resonance (FMR) technique for different cobalt implantation doses. The FMR data show that the easy and hard axes have a periodicity of 60 degrees in the film plane, in agreement with the hexagonal structure of the ZnO films. This six-fold in-plane magnetic anisotropy, which is observed for the first time in ZnO-based diluted magnetic semiconductors, is attributed to the substitution of cobalt on Zn sites in the ZnO structure, and a clear indication for long range ferromagnetic ordering between substitutional cobalt ions in the single-crystalline ZnO films.Comment: 7 pages, 4 figure

Reversing the training effect in exchange biased CoO/Co bilayers

We performed a detailed study of the training effect in exchange biased CoO/Co bilayers. High-resolution measurements of the anisotropic magnetoresistance (AMR) are consistent with nucleation of magnetic domains in the antiferromagnetic CoO layer during the first magnetization reversal. This accounts for the enhanced spin rotation observed in the ferromagnetic Co layer for all subsequent reversals. Surprisingly, the AMR measurements as well as magnetization measurements reveal that it is possible to partially reinduce the untrained state by performing a hysteresis measurement with an in plane external field perpendicular to the cooling field. Indeed, the next hysteresis loop obtained in a field parallel to the cooling field resembles the initial asymmetric hysteresis loop, but with a reduced amount of spin rotation occurring at the first coercive field. This implies that the antiferromagnetic domains, which are created during the first reversal after cooling, can be partially erased.Comment: 4 pages, 4 figure

Domain Structure and Magnetoresistance in Co2MnGe Zigzag Structures

AbstractWe report a clear manifestation of the negative contribution to the magnetoresistance due to domain walls in Co2MnGe-Heusler submicron zigzag wires in which the domain structure, domain size and domain wall density can be well controlled. The magnetic behavior of these systems results from the interplay between the intrinsic magneto-crystalline (K4) anisotropy, growth induced uniaxial (KU = 4.7x103 J/m3) anisotropy and shape anisotropy (KS), as observed by magnetic-force microscopy (MFM) and longitudinal Kerr hysteresis loop measurements. Magnetoresistance measurements were performed by the four-point method under a field applied in the plane of the wires at a temperature of 300K. In these structures, domain wall-creation and annihilation occur in a coherent way. As a result, clear jumps of the resistance are detected during the transition from single-domain- to multi-domain states. At room temperature a value RDW = -2.5 mΩ was obtained; this result is the same order of magnitude as other experimental and theoretical findings. The negative resistive contribution due to the domain wall is also discussed and compared with the existing theoretical models