Flux-closure Structures Research Articles

Ultrafast switching of magnetic nanoelements using a rotating field

Nanostructured granular Ni80Fe20 and Co films are studied using a 3D hybrid finite element/boundary element model. Switching dynamics are calculated for external fields applied unidirectional after a rise time of 0.1 ns and for a 10 GHz rotational field with a field strength of Hext=0.2 Js/μ0 (160 kA/m for NiFe and 280 kA/m for Co). The transient magnetization patterns show that reversal in the unidirectional field proceeds by the nucleation and propagation of end domains towards the center of the element. The switching time strongly depends on the Gilbert damping parameter α. Materials with uniaxial anisotropy (Co), require larger field, but exhibit shorter switching times. Reversal in rotational fields involves inhomogeneous rotation of the end domains towards the rotational field direction leading to partial flux-closure structures. Shorter switching times are obtained by the application of the 10 GHz rotational field (tsw=0.05 ns). Precessional oscillation effects after abruptly switching off the external field which occurred in the NiFe square element, were suppressed in the granular Co film. Reducing the field to zero slowly inhibits the high frequency excitations in NiFe.

Recent Development and Application of LEEM/PEEM. Magnetic Domain Imaging of Magnetic Nano-structures Observed by Photoemission Electron Microscopy.

We have observed magnetic domains of magnetic nano-structures of nickel by photoemission electron microscopy (PEEM) using synchrotron radiation. The magnetic nano-structures were fabricated by electron beam lithography and lift-off. From the magnetic contrast observed by PEEM and micromagnetic simulations, it is indicated that the square, hexagonal and circular structures form flux closure structures whereas the triangular structure does not form the flux closure structure.

The temperature dependence of the magnetic domain structure in thin cobalt crystals

Abstract The temperature dependence of the magnetic domain structure of thin cobalt crystals in the range 20°c to 250°c has been investigated as a function of crystal thickness and orientation. Comparison is made between experimental results obtained by Lorentz electron microscopy and a calculation giving the domain structure of any uniaxial crystal having a 'free-pole' structure, such as is observed in thin cobalt crystals (⋦3–4000 A thick), when the magnetization makes an angle (0→π/2°) with the crystal surface. The calculation used is that due to Jakubovics (1966) and is modified by considering the decrease of anisotropy energy with temperature. The formation of flux closure structures at non-magnetic inclusions under conditions of reduced anisotropy is also considered.