Magnetic nanostructures: Synthesis, properties, and applications

Abstract

Advances in magnetic nanostructures are rapid in the field of science and technology due to the unique magnetic properties observed at the nanoscale such as superparamagnetism, enhanced magnetic moment, high saturation field, shape anisotropy, etc. The common morphologies of magnetic nanostructures are dots, nanoparticles, nanocrystals, nanowires, nanotubes, and thin films. With the emergence of new synthesis and fabrication techniques, magnetic nanomaterials with diverse shapes and sizes have been fabricated characterization technique magnetic nanostructure and their structure-property relationships established. Characterization techniques such as magnetic magnetic force microscopy (MFM) Lorentz microscopy force microscopy (MFM), Lorentz microscopy, magnetometry based on superconducting superconducting quantum interference device (SQUID) quantum interference device (SQUID), and small-angle neutron scattering small angle neutron scattering (SANS) (SANS) have been utilized to study magnetism in nanostructures. In this chapter, the magnetism of atoms is discussed and the effect of nanostructuring on magnetic properties is magnetic length scale reviewed. Characteristic magnetic length scales are presented. When the size of magnetic materials, in at least one dimension, becomes comparable to characteristic magnetic length scales, size-specific magnetic properties such as superparamagnetism, remanence enhancement, random anisotropy, and giant giant magnetoresistance (GMR) magnetoresistance (GMR) effects are observed. The change in magnetic moment and anisotropy with dimensionality is discussed; e.g., broken symmetry at surfaces and interfaces may increase magnetic moment compared with the bulk counterpart. In nanostructured materials, shape and surface anisotropy is induced and thickness dependence of anisotropy is observed in thin films. Magnetization reversal mechanisms and the use of micromagnetic modeling in establishing microstructure-property relationships micromagnetic modeling magnetization reversal mechanism are discussed. Magnetic nanostructures such as particles, nanowires, nanorings, thin films, and molecular nanomagnets are reviewed. Current trends in synthesis molecular beam epitaxy (MBE) by physical (melt spinning, ball milling, sputtering, and molecular beam epitaxy (MBE)) and chemical (reduction, self-assembly, and electrodeposition) processes are outlined. The use of atomic Mössbauer spectroscopy force microscopy, Mössbauer spectroscopy, electron holography, scanning electron microscopy, and transmission electron microscopy is discussed. The magnetic properties of hard and soft nanostructured magnets are reviewed. Exchange-coupled nanocomposites and the GMR effect are also magnetic nanostructure application data storage discussed. Applications of magnetic nanostructures in data storage and biomedical applications are summarized.