Understanding the correlation between magnetic properties and nanostructure involves collaborative efforts between chemists, physicists, and materials scientists to study both fundamental properties and potential applications. This article introduces a classification of nanostructure morphology according to the mechanism responsible for the magnetic properties. The fundamental magnetic properties of interest and the theoretical frameworks developed to model these properties are summarized. Common chemical and physical techniques for the fabrication of magnetic nanostructures are surveyed, followed by some examples of recent investigations of magnetic systems with structure on the nanometer scale. The article concludes with a brief discussion of some promising experimental techniques in synthesis and measurements.

Magnetic Properties of Nanostructured Materials

We demonstrate a powerful and practical method of characterizing interactions in fine magnetic particle systems utilizing a class of hysteresis curves known as first order reversal curves. This method is tested on samples of highly dispersed magnetic particles, where it leads to a more detailed understanding of interactions than has previously been possible. In a quantitative comparison between this method and the δM method, which is based on the Wohlfarth relation, our method provides a more precise measure of the strength of the interactions. Our method also has the advantage that it can be used to decouple the effects of the mean interaction field from the effects of local interaction field variance.

Characterizing interactions in fine magnetic particle systems using first order reversal curves

This paper discusses the principles of magnetic force microscopy (MFM) and its application to magnetic recording studies. We use the ac detection method which senses the force gradient acting on a small magnetic tip due to fields emanating from the domain structure in the sample. Tip fabrication procedures are described for two types of magnetic tips: etched tungsten wires with a sputter‐deposited magnetic coating and etched nickel wires. The etched nickel wires are shown to have an apex radius on the order of 30 nm and a taper half‐angle of approximately 3°. Lorentz‐mode transmission electron microscopy of the nickel tips reveals that the final 20 μm is essentially single domain with magnetization approximately parallel with the tip axis. Images of written bit transitions are presented for several types of magnetic media, including CoPtCr, CoSm, and CoCr thin films, as well as γ‐Fe2O3 particulate media. In general, the written magnetization patterns are seen with high contrast and with resolution better ...

Magnetic force microscopy: General principles and application to longitudinal recording media

The current state of the art of electrostatic force microscopy (EFM) is presented. The principles of EFM operation and the interpretation of the obtained local voltage and capacitance data are discussed. In order to show the capabilities of the EFM method, typical results for semiconducting nanostructures and lasers are presented and discussed. Improvements to EFM and complementary electrical methods using scanning microscopy demonstrate the continuing interest in electrical probing at the nanoscale range.

https://iopscience.iop.org/article/10.1088/0957-4484/12/4/321/pdf

Electrostatic force microscopy: principles and some applications to semiconductors

We present a transfer-function approach to calculate the force on a magnetic force microscope tip and the stray field due to a perpendicularly magnetized medium having an arbitrary magnetization pattern. Under certain conditions, it is possible to calculate the magnetization pattern from the measured force data. We apply this transfer function theory to quantitatively simulate magnetic force microscopy data acquired on a CoNi/Pt multilayer and on an epitaxially grown Cu/Ni/Cu/Si(001) magnetic thin film. The method described here serves as an excellent basis for (i) the definition of the condition for achieving maximum resolution in a specific experiment, (ii) the differences of force and force z-derivative imaging, (iii) the artificial distinction between domain and domain wall contrast, and finally (iv) the influence of various tip shapes on image content.

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Quantitative magnetic force microscopy on perpendicularly magnetized samples

The nature of media recording noise in metallic, quasiparticulate thin films is principally related to the grain size, crystallographic orientation, and intergranular exchange and magnetostatic coupling in the films. In this study the results of a magnetic evaluation of magnetostatic interactions in CoNiCr thin films of varying Cr underlayer thickness are reported. The evaluation is undertaken through the measurement and comparison of remanence curves. The results presented here indicate enhanced cooperative switching as Cr underlayer thickness is reduced from 2000 to 100 A, with a strong correlation between signal‐to‐noise measurements. In addition, the transition from principally exchange‐coupled to quasiparticulate thin films, as Cr underlayer thickness increases, has been established.

A magnetic evaluation of interaction and noise characteristics of CoNiCr thin films

Magnetic measurement of interaction effects in CoNiCr and CoPtCr thin film media

Several techniques are presented which allow magnetic force microscopy to be performed while simultaneously mapping the surface topographic features of a magnetic sample. The separation of magnetic and topographic features measured simultaneously with a scanning force microscope is made possible by an instrument based on a differential interferometer that can detect cantilever deflections of 0.005 nm at a frequency as low as 1 Hz. Two different applications are presented.

Separation of magnetic and topographic effects in force microscopy

Signal and media noise measurements have been made for a wide variety of Co‐alloy longitudinal magnetic recording media A strong correlation between media noise and the coercivity squareness, S*, is observed at high transition density The optimum ratio of isolated pulse amplitude to media noise is found for S*≂075 This behavior arises from reduced ferromagnetic exchange coupling between neighboring grains of the film which influence both the coercivity squareness and also the uniformity of the domain boundary at the recorded transitions The low‐noise characteristics of sputtered γ‐Fe2O3 also appear to correlate with low values of coercivity squareness This work confirms that for systems in which media noise is a limiting factor, optimum performance may require considerably lower values of coercivity squareness than commonly used, determined by the relative contribution of media noise to the overall system noise

Influence of coercivity squareness on media noise in thin‐film recording media

The basic magnetic characterization techniques for thin recording media are critically examined in relation to the requirements for modern high-storage-density materials. The applicability and usefulness of remanence curves for the characterization of thin-film media are discussed together with the recently developed Delta I(H) technique. The origins of the relation between these measurements and cooperative reversal are presented, together with the improved data showing the correlation between Delta I(H) and noise. This discussion is extended to include the time-dependent phenomena and in particular the activation volume, including the effects of intergranular coupling. Data are presented to show these effects in both single-layer alloy films and laminated systems, and the implications for ultimate recording density are discussed. >

I.L. Sanders

Papers

A magnetic evaluation of interaction and noise characteristics of CoNiCr thin films

Magnetic measurement of interaction effects in CoNiCr and CoPtCr thin film media

Separation of magnetic and topographic effects in force microscopy

Influence of coercivity squareness on media noise in thin‐film recording media

Magnetic characterisation of thin film recording media