Magnetism and magnetic materials have been subjects of considerable interest for more than 3000 years, going back to ancient times. In modern times, myriad are the applications of magnetism and magnetic materials ranging from generation of electrical power to communications and information storage. Magnetic materials are absolutely indispensable in modern technology, and the intensity and importance of their applications are reflected in the multi-billion dollar market for magnetic materials in three broad areas: permanent magnets, soft magnets, and the magnetic recording medium. Continuous evolution in the field of magnetic materials has not, however, remained confined only to these well-identified areas. It is now well recognized that fresh applications are possible through the coupling of magnetism with other physical properties of materials such as magneto-thermal, magneto-elastic, magneto-optic, and magneto-electrical couplings. Newer classes of magnetic materials are being discovered with interesting new functions stimulating further growth of newer technology in various areas including information technology, wireless communication, microelectronics, biotechnology, and such like.

Against this backdrop, it is natural that the subject of magnetism finds a prominent place in solid state/condensed matter physics textbooks taught in the advanced undergraduate and postgraduate courses at universities all over the world. However, this coverage is mostly confined to a basic understanding of the phenomenon of magnetism as one of the physical properties of solid materials within the general framework of quantum mechanics. Detailed theoretical exposition of the subject is left to the specialized books on magnetism, and there are not too many of such books. Unlike high energy and particle physics, magnetism with its huge potential in technological applications is mostly an experimental science, where experimental techniques and related instruments play a very crucial role. The quantum many-body theories of magnetism (and for that matter condensed matter physics in general) are continuously evolving to explain the classes of emerging phenomena being discovered through experimental work on magnetic materials (and other classes of condensed matter). It is experimentation which is leading the field in the case of condensed matter/magnetism rather than theory as in the case of high energy and particle physics.

In the area of high energy and particle physics, the students are at least aware of the necessary theoretical techniques and the relevant experimental methods before they enter the research field at the Ph.D. level.

The book begins with an exposition of the interesting history of magnetism and magnetic materials. This is followed by a short chapter discussing the role of magnetism and magnetic materials in modern society and current technological applications of magnetic materials and devices. This second chapter highlights why magnetism is considered to be more of an applied or experiemntal science rather than a theoretical one.

The meaning of the stress tensor is elucidated and its representation with the Mohr circle is presented.

Symmetry is introduced as a basic notion of physics and, in particular, for soil mechanics also. Isotropy and anisotropy are discussed. A special case of isotropy of space is the principle of material frame indifference which plays an eminent role in the development of constitutive equations. The geometric scaling is discussed together with the notion of a simple material, which is – often unconsciously – basic in geotechnical engineering. Invariance with respect to stress and time scales is discussed. Mechanical similarity and the associated Pi theorem is shown to be the basis for the evaluation of so-called physical simulations with model tests.

A very short and simple introduction to vectors and tensors and some related quantities.

It is shown that the typical paths obtained with element tests can be inferred by reasoning if some basic properties of proportional paths are taken into account.

The notion of collapse and its importance in geotechnical engineering is introduced. The two main approaches are explained: (i) stress fields that fulfil the Mohr–Coulomb limit condition (together with slip line analysis as an application of the method of characteristics) and (ii) analysis of collapse mechanisms consisting of rigid blocks. The harmonisation of codes and the problematic definition of safety on the basis of probability theory are discussed.

As an important application of the theory of elasticity in soil mechanics, the main principles of elastodynamics are introduced. On the basis of waves in 1D-continua the notions of transmission, reflexion and dynamic stiffness are explained, and the body waves are presented as compression and shear waves. Rayleigh waves are presented as an example of surface waves.