Particulate and Granular Magnetism

Abstract

Abstract This text is concerned with magnetic nanoparticles and granular thin films which form the basis of all advanced magnetics technology excluding permanent magnets and soft materials for inductors and transformers. The first part of the text is concerned with fundamental concepts. Thereafter chapters are presented on magnetic domains including basic principles but then restricted to domains in granular thin films and single domain particles including coherent and incoherent reversal and the effects of exchange coupling. Particular emphasis is then placed on thermal activation effects and the role of a particle or grain size distribution and the measurement techniques by which the effects of thermal activation can be measured. This part concludes with a detailed discussion of the phenomenon of exchange bias and magneto-resistance in multilayers. Part two includes the description of three dominant forms of technology using particulate and granular magnetic materials. The first of these is ferrofluids including engineering applications in seals and loudspeakers but then looking at the rapidly developing field of biomedical applications in general and in particular the phenomenon of magnetic hyperthermia. The second major application is the field of magnetic recording which is addressed including tape recording and heat assisted magnetic recording (HAMR). Finally the development and implementation of magnetic random access memory (MRAM) is described including the commercialisation of MRAM using bits oriented perpendicular to the plane and switched by spin transfer torque (STT) and read via magneto-resistance using tunnelling magneto resistance (TMR). Finally a brief outlook of future potential developments is described.