Magnetoconductivity in a mesoscopic antidot array

Nanotechnology, 2013

We study the reversal mechanisms in a self-assembled, hexagonally ordered Fe antidot array with a period of 200 nm and an antidot diameter of 100 nm which was prepared by polystyrene nanosphere lithography. Direction-dependent information in such a self-assembled sample is obtained by measuring the anisotropic magnetoresistance (AMR) through constrictions processed by focused ion beam milling in nearest neighbor and next nearest neighbor directions. We show that such an originally integral method can be used to investigate the strong in-plane anisotropy introduced by the antidot lattice. The easy and hard axis reversal mechanisms and corresponding AMR signals are modeled by micromagnetic simulations. Additional in-field magnetic force microscopy studies allow the correlation of microscopic switching to features in the integral AMR. We find that the easy axis of magnetization is connected to a distinct periodic magnetic domain pattern, which can be observed during the whole magnetization reversal. While this process is driven by nucleation and propagation of reversed domains, the hard axis reversal is characterized by a (stepwise) rotation of the magnetization via the antidot lattice' easy axes.

Physical Review B, 2007

The dynamic magnetic properties of two-dimensional periodic Co antidot arrays were studied by X-band ferromagnetic resonance. The experimental results on geometrically scaled antidot arrays reveal a strong attenuation of the uniform ferromagnetic resonance mode in comparison to a continuous film, but an excitation of nonuniform in-plane spin-wave modes. Micromagnetic finite-element simulations show that the static magnetic structure in an antidot array depends on the direction of the external field with respect to the symmetry axes of the antidot lattice, even if the external field is strong enough to enforce a technically saturated magnetization state. The analysis gives evidence that characteristic inhomogeneities in the magnetization distribution around the antidots give rise to the changes of the resonance modes with the in-plane direction of the magnetization.

Superlattices and Microstructures, 1991

Physical Review B, 1998

We have studied magnetoresistivity oscillations in rectangular lateral antidot superlattices both in lowtemperature electron transport experiments as well as in a classical diffusion model. Within this model, the conductivity tensor is obtained from a numerical simulation of the spatial distribution of electrons diffusing in the antidot array. It is demonstrated that all the essential features of the measured magnetoconductivity can be reproduced within this classical model. Maps of the trajectories in real space give an intuitive understanding of the mechanism that causes the anisotropies in the conductivity.

Journal of Low Temperature Physics, 2010

The absence of the superparamagnetic limit in nanostructured antidots makes them strong candidates for ultra-high density recording media. In this work, nanoporous alumina templates (NpATs), with average pore diameters ∼35 nm and separation ∼100 nm, were grown using a two-step anodization method. A Ni 80 Fe 20 thin film of 6.5 nm was then sputtered on top of such NpATs, building an antidot network. A detailed study of the magnetoresistance (MR) (fields up to 25 T and temperatures down to 77 K) was performed. The antidot network sample revealed an anomalous MR and R(T ) behaviour at T M ∼ 250 K arising from a spin-flip transition occurring in a thin iron oxide layer.

Journal of Applied Physics - J APPL PHYS, 2007

Permalloy antidot arrays with different square hole sizes (1200×1200, 800×800, and 400×400 nm2) have been fabricated by means of electron-beam lithography and lift-off techniques. The smaller square hole size results in enhanced remanence and reduced coercivity in the antidot array. Multiple resonance modes were clearly observed for the magnetic field applied normal to the array plane, and double uniform resonance modes occurred when the field deviated more than 30° from the normal to the plane. Two distinct dipolar field patterns with different orientations and magnitudes split the uniform resonance into double resonance modes. The double resonance modes show uniaxial in-plane anisotropy and the easy axes are orthogonal. The magnitude of the induced dipolar anisotropy remains almost constant with changes in the square hole size. The double resonance peaks move to low field with reduction of the square hole size.

The Open Surface Science Journal, 2012

EPL (Europhysics Letters), 2008

The broad prospects for the practical uses of magnetic nanostructures make the control of their magnetization reversal processes a very relevant research field, particularly considering that different processes, associated to largely different sets of hysteretic parameters, can be implemented through the control of the shape and size of the nanostructures. We analyze in this work, within the framework of a micromagnetic model, the magnetization reversal processes occurring in antidot arrays and, in particular, the efficiency of these arrays as i) pinning structures for the propagation of externally to the array nucleated domain walls and ii) nucleation centers for the magnetization reversal processes from within the array. From our simulational analysis, whose results we have experimentally validated, it is concluded that the measurement of the angular dependence of the coercive force can be used as a useful tool to identify the actually occurring reversal process.

Applied Physics Letters, 2006

We present studies on magnetic anti-dot nano-structures with three-dimensional ͑3D͒ architectures, fabricated using a self-assembly template method. We find that patterning transverse to the film plane, which is a unique feature of this method, results in novel magnetic behavior. In particular, one of the key parameters for a magnetic material, the coercive field B c , was found to demonstrate an oscillatory dependence on film thickness.

AIP Advances, 2019

The magnetic properties of a Permalloy antidot array in square lattice geometry, with circular-rhomboidal hole shape and fabricated by interference laser lithography and ion-beam sputtering have been reported. Magneto-optical Kerr effect magnetometry indicated that the sample exhibits four-fold anisotropic behaviour, i.e. different magnetization loops were observed when the external magnetic field was applied along either x-or y-axis, or along the array diagonal. Broadband ferromagnetic resonance measurements revealed a rich variety of different magnetization configurations in the unsaturated state that can be controlled by the orientation of the external magnetic field. Micromagnetic simulations have been performed to explain the observed results. On the contrary, in the saturated regime the system demonstrated almost isotropic magnetic behaviour that improves with external field increase. The obtained results show the potential of interference lithography for the fabrication of large area antidot arrays.