M. Maicas

Induction of bistability in low-magnetostriction amorphous ribbons

Abstract Bistability phenomena recently observed in amorphous wires can be explained by magnetoelastic coupling between two zones with different anisotropy. In this work we show the induction of bistability in amorphous ribbons with low magnetostriction (Metglas 2705M) using the exchange coupling in zones with a continuous varying anisotropy direction.

Micromagnetic structures in square magnetic nanodots

Abstract The structure of magnetization in magnetic square dots is studied in the range of tens of nanometer by means of micromagnetic simulations. Two magnetic configurations are found, diagonal and vortex structures for thin films, flower and vortex for magnetic nanocubes and a hybrid flower in bulk and vortex near the surfaces for dots with thicknesses larger than dot edge length.

Interaction between a Bloch domain wall and a pinning plane

Abstract A numerical simulation of the interaction between a Bloch domain wall and an one-dimensional anisotropy modulation has been done. Different pinning planes were simulated with several anisotropy modulations. The results show the velocity, shape and domain wall energy as a function of the distance between the wall and the pinning plane. The magnetic fields necessary to overcome the different pinning planes have been obtained.

Domain-wall magnetostatic coupling in permalloy/Cu sandwiches

We have studied, by means of numerical simulation, the structure of domain walls in permalloy thin film monolayers and sandwiches consisting of two permalloy layers separated by a Cu interlayer. The calculated transition thicknesses between Bloch and Neel domain walls increase notably for the sandwiches with respect to monolayers. The structures obtained for uncoupled walls show quite similar patterns for the Neel walls and their corresponding quasi-walls. When coupled, the quasi-walls disappear and so the energy of the pair is reduced approximately to half the energy of the uncoupled pair. Results have been tested in thin film permalloy sandwiches obtained from a sputtering system.

Study of domain walls in Fe20Ni80 and Fe20Ni80/Cu/Fe20Ni80 thin films

Abstract Fe20Ni80 single layers and Fe20Ni80/Cu/Fe20Ni80 thin films were grown by using a magnetron sputtering system in order to study the domain wall structures in both kinds of samples. The magnetostatic coupling energy between the domain walls in the sandwich structures has been obtained. When there is no coupling, these structures exhibit Cross—Tie domain walls.

Domain-wall patterns in magnetostatically coupled bilayers

Abstract Magnetic domain-wall patterns in magnetostatically coupled bilayers separated by a non-magnetic interlayer have been studied for different anisotropy configurations. A numerical treatment is presented for the case of a parallel anisotropy axis between magnetic layers for samples with thicknesses of 1000Afor the magnetic layers and 100Afor the interlayer. For these thicknesses coupled Neel walls appear with a similar structure to that found in previous works on thinner films except for the much higher magnetic poles found at the interlayer boundary surfaces. Samples of Fe 20 Ni 80 /Cu/Fe 20 Ni 80 of 500/200/500Athickness have been grown whilst uniaxial anisotropies were induced in the magnetic layers with the perpendicular easy axis directions between them. Bitter observations show that coupling between domain walls also exists in samples with the non-parallel magnetic anisotropy axis in both layers.

Influence of domain wall stabilization on dynamic losses in amorphous ribbons

Abstract Dynamical hysteresis losses in amorphous magnetic materials depend mainly on the micro eddy currents. This effect can be enhanced by domain wall (DW) stabilization phenomena, since the anisotropy modulation induced by a stabilized DW behaves like a pinning plane. The irreversible displacement of a DW that overcomes this kind of defect produces an increase of micro-eddy currents that can be an important part of the total hysteresis losses.

Single Point Gradiometer for Planetary Applications

We have designed and fabricated a microelectromechanical device, based on the alternating field gradient concept, to measure surface magnetic field gradient on planets. Its sensitivity is 4 10-4 T/m, which is appropriate for magnetite outcrops and areas with rocks formed at different stages recording geomagnetic field reversals. We present the results obtained with three different prototypes.

Anomalous domain wall displacement in amorphous samples under transversal magnetic fields

Abstract The displacement of longitudinal domain walls by the effect of transversal magnetic fields has been studied in amorphous ribbon samples by means of a numerical simulation. The magnetic pole distribution derived from the domain wall structure near the surface can be used to explain this unexpected transversal displacement.