Chapter 11 Transport and Magnetic Properties of Nanogranular Metals

Abstract

Physical properties of solids containing metal granules of several nanometers, embedded into a dielectric matrix, are described in this chapter. The ion-beam sputtering (IBS), electron-beam sputtering (EBS) and magnetron sputtering (MS) with subsequent annealing are considered as main methods for such materials production. Magnetic, electrical and galvanomagnetic properties of nanogranular metals differ drastically from those of homogeneous materials. They are strongly dependent on metal volume fraction and show very peculiar features in the vicinity of the percolation threshold. The unique properties of nanogranular metals make them prospective candidates for a wide range of possible applications. The magnetic properties are described as a function of magnetic grain sizes and shapes; different possible states such as ferromagnetic, superparamagnetic and cluster glass as well as transition between them are discussed. Special attention is paid to transport properties (resistance and Hall effect) because they are very sensitive to external parameters being the base for working mechanisms in many types of sensors and devices. The magnetic field and temperature dependences of resistance and Hall effect are considered in the framework of the percolation theory. Various types of magnetoresistances such as giant and anisotropic ones as well as their mechanisms are under discussion. The influence of the various types of quantum effects and, in particular, of the quantum-size effect on the electronic transport in granular metals is described in the vicinity of the percolation transition.