J. Iñiguez

Micromagnetic tailoring of periodic antidot permalloy arrays for high density storage

A micromagnetic study on antidot permalloy arrays is carried out in order to delimit their possibilities for high density storage. The dependence of the recorded bit quality on antidot size, separation distance, and film thickness is reported as well as hysteresis loops and coercivities. The simulations show a limit for the antidot size around 80 nm leading to maximum areal storage densities of about 10 Gbits/in2. The results are interpreted in terms of demagnetizing, anisotropy, and exchange energies’ balance.

Automatic disaccommodation measuring system

Magnetic after effect measurement constitutes an advantageous procedure for the investigation of point defects giving considerable information about the crystal lattice dynamics. Unfortunately, most standard measuring methods involve tedious impedance bridges which are not suitable for systematic research. Thus a new automatic measuring system, based on the use of an inductance-capacitance resistor LCR meter, has been developed with special emphasis on soft magnetic materials. The resolution capability of our system is pointed out by measuring the disaccommodation of a ferrite sample.

REMANENT STATES IN PERIODIC ANTIDOT PERMALLOY ARRAYS

It has been recently suggested that periodic antidot arrays in magnetic media could be a suitable system for high density data storage because hard axis magnetic switching has remanence and hence, memory. In this work a numerical micromagnetic study of periodic antidot permalloy arrays is presented. Remanent states are obtained after saturation of the sample along the hard axis direction for different antidot sizes w (0.32 μm⩽w⩽2.16 μm) and different separation distances d between antidots (w/2⩽d⩽3w). Our micromagnetic model allows us to study these systems beyond the experimental results presently available so that we can explore the high density limit. The signal to noise ratio decreases significantly for separation distances d⩾w and increases steadily with the antidot size w in the range analyzed. The remanent configurations are similar to the experimental data obtained by scanning Kerr microscopy.

Data processing for magnetic disaccommodation spectroscopy

The authors address the problems of analyzing experimental data obtained from magnetic disaccommodation measurements in order to extract information about the nature of the underlying phenomena. Some data processing methods commonly used in this type of investigation are reviewed, and novel techniques aimed at the optimization of the signal-to-noise ratio, the separation of overlapping modes and the determination of the relaxation parameters are discussed. The analysis strategies are divided into two groups: correlation techniques, characterized by different weighting functions and transform techniques, based on the use of the Fourier and Laplace transforms. As an example application, the relaxation process III in a vacancy-doped magnetite sample is analyzed. >

Influence of sintering atmosphere on the magnetic after-effect in strontium ferrites

Copyright (c) 1996 Elsevier Science B.V. All rights reserved. The relaxation of the initial permeability after sample demagnetization has been measured in polycrystalline strontium ferrite samples with nominal composition SrO.6Fe 2 O 3 (M-phase), sintered under different oxygen pressures, and has been represented by isochronal curves. Very different behaviours are observed. With lower oxygen pressures the isochronal spectra are similar to the curves obtained for barium ferrites, with relaxation peaks at room temperature. In higher oxygen partial pressures, the relaxation peaks are found at lower temperatures.

Giant magnetoimpedance effect enhancement by circuit matching

GMI response of amorphous wires can be greatly increased by working at resonant conditions in a LC cell. This feature of the circuit can be exploited to increase the sensibility of current GMI-based sensors while selecting the working frequency.

Effect of slowly relaxing impurities on ferrimagnetic resonance linewidths of single crystal nickel ferrites

Ferrimagnetic resonance (FMR) linewidths have been measured at X-band frequencies (11 GHz) from 77 K to 400 K in single crystal nickel ferrites with composition Ni/sub x/Fe/sub 3-x/O/sub 4/ with x=0.9, 1.0, 1.2. Measurements have been carried out by means of an automatic technique based on a modified short-circuit SMA transmission line. Linewidths ranged from 40 Oe to 80 Oe in all the temperature range. The dependence of the FMR linewidth with temperature leads to a contribution of the valence-exchange mechanism for x 1. The collection of data obtained by the automatic system allows the authors to achieve the values for the relaxation times and activation energies of these mechanisms. >

Aerodynamics of a cycling team in a time trial: does the cyclist at the front benefit?

When seasonal journeys take place in nature, birds and fishes migrate in groups. This provides them not only with security but also a considerable saving of energy. The power they need to travel requires overcoming aerodynamic or hydrodynamic drag forces, which can be substantially reduced when the group travels in an optimal arrangement. Also in this area, humans imitate nature, which is especially evident in the practice of outdoor sports and motor competitions. Cycle races, in which speeds of up to 15 m s−1 are frequent, offer great opportunities to appreciate the advantage of travelling in a group. Here we present a brief analysis of the aerodynamics of a cycling team in a time-trial challenge, showing how each rider is favoured according to his position in the group. We conclude that the artificial tail wind created by the team also benefits the cyclist at the front by about 5%.

Study of the conductivity of a metallic tube by analysing the damped fall of a magnet

The fall of a magnet through a hollow conducting tube is described. Although this experiment is well known, a detailed treatment by means of a circuit analysis allows us to relate the conductivity of the tube to the characteristic parameters of the experiment.

Micromagnetic switching of patterned square magnetic nanostructures

Micromagnetic simulations of switching processes in planar square magnetic nanoelements are presented. Nanosquares of size “a” in the range 10 lex<a<110 lex (lex being the exchange length, lex=(A/2πMs2)1/2) and thickness “t”, 0.25 lex<t<2 lex have been studied. Two different switching modes have been observed. The first one is basically found for very small nanoelements and it is close to uniform rotation while the second one takes place in the large nanosquares and presents an intermediate state. Good agreement of the computations with recent experimental measurements in Supermalloy is achieved. The shape of the hysteresis loops, the values of the coercivity, and the maximum in coercivity dependence with size are reproduced by the simulations. Furthermore, the two reversal mechanisms are shown to be the cause of such maximum in coercivity such as the different shapes of hysteresis loops.