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A spin valve giant magnetoresistive (GMR) or tunnel magnetoresistive (TMR) head is designed to exhibit a transfer curve, which is sensitive, non-hysteric, linear, and noise free. The basic approach to achieve these properties is to make the easy axis of the free layer parallel to an air bearing surface (ABS) and a longitudinal domain bias technique is employed to magnetise the free layer along its easy axis to saturation so that a single domain state is obtained in the free layer and the head is free from Barkhauson noise during its operation. The most commonly used domain bias techniques are permanent magnet biasing (PM biasing) and antiferromagnet exchange-tab biasing (AF exchange-tab biasing). However, these existing domain bias techniques are becoming obsolete as the continued miniaturization of sensors is approaching the nanometre regime. This paper will first review the basic principles, advantages and disadvantages of the existing domain bias techniques. We will then present our recent work on a new domain bias technique for nanoscale magneto-electronic devices employing interlayer exchange coupling and spin flop of synthetic antiferromagnets. [ABSTRACT FROM AUTHOR]

Magnetic anisotropies of epitaxial ultra-thin iron films grown on the surface reconstructed GaAs substrate have been studied. Ferromagnetic resonance (FMR) technique has been exploited to determine magnetic parameters of the films in the temperature range 4-300 K. The unusual angular dependence of FMR spectra allowed us to build precise model of the magnetic anisotropies of the studied systems. Presence of strong perpendicular anisotropy have been deduced. Switching of the principal anisotropy axes has been observed in the double ferromagnetic-layer sample. It has been attributed to drastic relaxation of the uniaxial component of anisotropy induced by the surface reconstruction of the substrate. The linear variation of magnetic anisotropy parameters with the temperature has been observed and discussed in terms of magneto-elastic anisotropies controlled by thermal expansion coefficients of the materials in a contact. [ABSTRACT FROM AUTHOR]

The discoveries of antiferromagnetic coupling in Fe/Cr multilayers by Grünberg, the Giant MagnetoResistance by Fert and Grünberg and a large tunnelling magnetoresistance at room temperature by Moodera have triggered enormous research on magnetic thin films and magnetoelectronic devices. Large opportunities are especially opened by the spin dependent tunnelling resistance, where a strong dependence of the tunnelling current on an external magnetic field can be found. Within a short time, the quality of these junctions increased dramatically. We will briefly address important basic properties of these junctions depending on the material stacking sequence of the underlying standard thin film system with special regard to complex interdiffusion properties. New materials with potentially 100% spin polarization will be discussed using the example of the full Heusler compound Co2MnSi, where we obtain up to 100% TMR at low temperature. Next, we discuss scaling issues, i.e. the influence of the geometry of small tunnelling junctions especially on the magnetic switching behaviour down to junction sizes below 0.01 µm2. The last part will give a short overview on field programmable logic circuits made from magnetic tunnelling cells, where we demonstrate the clocked operation of a programmed AND gate. [ABSTRACT FROM AUTHOR]

We report on sizable antiferromagnetic interlayer exchange coupling (AFC) of Fe(001) layers across epitaxial Si spacers, for which epitaxial growth of a pseudomorphic phase stabilized by the interface is confirmed by low-energy electron diffraction and high-resolution transmission electron microscopy. The coupling strength decays with spacer thickness on a length scale of a few Å and shows a negative temperature coefficient. Transport measurements of lithographically structured junctions in current-perpendicular-to-plane geometry show the validity of the three "Rowell criteria" for tunneling: (i) exponential increase of resistance R with thickness of the barrier, (ii) parabolic dI/dV-V curves, and (iii) slight decrease of R with increasing temperature. Therefore, AFC is mediated by non-conductive spacers, which in transport experiments act as tunneling barriers with a barrier height of several tenths of an eV. We discuss our data — in particular the strength, thickness and temperature dependence — in the context of two previously proposed models for AFC across non-conducting spacers. We find that neither the molecular-orbital model for heat-induced effective exchange coupling nor the quantum interference model extended to insulator spacers by introducing complex Fermi surfaces can account for the strong AFC across epitaxial Si spacers and its negative temperature coefficient. The recently proposed defect-assisted interlayer exchange coupling model, however, yields qualitative agreement with the enhanced AFC and the temperature dependence. [ABSTRACT FROM AUTHOR]

Epitaxial CrO2 thin films deposited on HF-cleaned TiO2 (100) substrates exhibit very strong strain anisotropy, while those grown without the HF treatment step are essentially strain-free and display bulk-like magnetic properties. The HF treatment enhances the surface smoothness of the TiO2 (100) substrates thus leading to the growth of epitaxially strained CrO2 films. The magnetic easy axis of these films changes orientation with thickness, switching from the in-plane c-axis direction for thick films to the b-axis direction for thinner films (< 50 nm). Similarly, over a thickness range, a change of the easy axis direction is also observed with lowering temperature. Ion-beam irradiation of the substrate surface prior to growth also results in the growth of strained CrO2 films, although the amount of strain is less than that observed for HF-treated substrates. The magnetic properties as a function of thickness have also been studied for as-deposited "thick" CrO2 films that are slowly chemically etched down in thickness. Unlike as-grown thin films below 50 nm thickness that have the easy axis along the b direction, the chemically etched down CrO2 thin films of equivalent thickness retain their easy axis alignment along the c-direction, but display a significantly enhanced coercivity. The observed differences in the switching behavior between the as-deposited films and those that are chemically etched can be qualitatively attributed to changes in the strain relaxation mechanism. [ABSTRACT FROM AUTHOR]

We examine different models and methods for studying finite-temperature magnetic hysteresis in nanoparticles and ultra-thin films. This includes micromagnetic results for the hysteresis of a single magnetic nanoparticle which is misaligned with respect to the magnetic field. We present results from both a representation of the particle as a one-dimensional array of magnetic rotors, and from full micromagnetic simulations. The results are compared with the Stoner-Wohlfarth model. Results of kinetic Monte Carlo simulations of ultra-thin films are also presented. In addition, we discuss other topics of current interest in the modeling of magnetic hysteresis in nanostructures, including kinetic Monte Carlo simulations of dynamic phase transitions and First-Order Reversal Curves. [ABSTRACT FROM AUTHOR]

Magnetic patterns with different shapes and aspect ratios provide control over the remanent domain state, the coercivity, and over different types of reversal mechanisms. We discuss magneto-optical, soft x-ray resonant scattering, and neutron scattering methods for evaluating the vector magnetization during reversal and the higher Fourier components of the magnetization distribution. These scattering methods, providing a statistical averaged signal, contrast real space methods, which give information on individual islands. [ABSTRACT FROM AUTHOR]

The paper demonstrates a possibility for effective modification of the thin-film material' chemical composition, structure and physical properties as result of selective removal of atoms by the certain energy ion beam. One of the most promising results of this effect is a production of devices with nanostructured high-density patterned magnetic media. [ABSTRACT FROM AUTHOR]

Photonic crystals, which are periodic composites of macroscopic dielectric media of different refractive index, affect the propagation of light in much the same way that semiconductor crystals affect the propagation of electrons. When photonic crystals are composed of magnetic materials such as rare-earth iron garnet, they are called as magnetophotonic crystals providing unique optical and magnetooptical properties. For instance, introduction of the magnetic material into the medium as a defect yields very large magneto-optical Faraday effect due to the localization of light at the magnetic defect. In this article, our recent investigations on one-dimensional magnetophotonic crystals composed of rare-earth iron garnet films such as Bi-substituted yttrium iron garnet (Bi:YIG) are summarized, and the very unique properties of the media are demonstrated for the films with (SiO2/Ta2O5)k/Bi:YIG/(Ta2O5/SiO2)k structures. [ABSTRACT FROM AUTHOR]

In this chapter recent synthetic progress in FePt and CoPt nanoparticles and nanoparticle arrays are summarized. The importance of monodisperse nanoparticles for future ultrahigh density data storage is mentioned. General chemical process for making magnetic nanoparticles and nanoparticle arrays is described. The synthetic progress that has been made so far and the problems indentified are summarize. Finally, possible future direction in the synthesis for practical high density recording applications is pointed out. [ABSTRACT FROM AUTHOR]

Scanning Hall probe microscopes have proven themselves to be quantitative and non-invasive tools for investigating magnetic samples down to 50 nm scale. They can be run in a wide range of temperatures and have unprecedented field resolution which is not affected by external fields. Local magnetometry of very small volumes is also feasible opening up very promising avenues for characterization of magnetic nanostructures. [ABSTRACT FROM AUTHOR]

Magnetic recording technology aims to provide the capability of storing as much as 1012 bits/in2 (1.6 × 1011 bits/cm2) in the foreseeable future. This remarkable storage density projection is made possible by recent major improvements in the microstructural and intrinsic magnetic properties of the thin film materials utilized for both recording and reading nanoscale magnetic domains which form the basis for digitally encoding information. To meet the Tb/in2 goal, further reductions in the recording medium grain size, the grain size distribution as well as increments in the magnitude of the magnetic anisotropy will be required. Currently used longitudinal recording materials are unlikely to support such high density targets and a migration to perpendicular recording is expected. On account of the superparamagnetic limit and the need for stringent control on the domain size, it is also likely that a transition to patterned media will also be required. The read sensor sensitivity will also need to increment to provide large enough signals needed for low error rate. Therefore, breakthroughs in magnetic thin films for the disk and head components will be required to meet the technology goals. [ABSTRACT FROM AUTHOR]