Introduction:
History and overview of spin electronics, Classes of magnetic materials:

Objectives:
The main objectives of this first lecture are
(a) to provide a history and a broad overview of spin electronics and
(b) to introduce briefly different classes of magnetic materials.

(a). History and overview of spin electronics:
Spin electronics (also termed as spintronics), at the interface between magnetism and electronics, is a new field of research in multidisciplinary level. The central theme is to manipulate actively the spin degrees of freedom in solid-state systems. In other words, the basic concept of spintronics is the manipulation of spin currents, in contrast to mainstream electronics in which the spin of the electron is mostly ignored. It is well known to the most of the students in science and engineering disciplines that every elemental particle (electrons, neutrons, photons and neutrinos, etc.) has a quantum mechanical property called 'spin' and it has a quantized value (including zero), which can be measured in principle. Adding this spin degree of freedom in the mainstream of electronics provides new effects, new capabilities and new functionalities, suitable for various futuristic magnetoelectronic applications.

It is important to know that there are three important factors making the spin of conduction electrons attractive for future technology, which are: (1) storing information using electron spin, (2) transformation of stored information (the spin can be transferred as it is attached to mobile carriers), and (3) the detection of stored information.

• Information can be stored in a system of electron spins because they can be polarized to either up or down states. To represent a binary digit (bit) state, for example, spin up may represent a high or '1' and spin down represent the low or '0' logic level.

• The second factor, the ability of information transfer by electron spins, relies on two facts: (i) electrons are mobile and (ii) electrons have a relatively large spin memory. Interestingly, conduction electrons "remember'' their spins much longer than they remember their momentum states.

• Finally, after the transformation of a spin state, it has to be detected. This is performed by observing the spin polarization either optically (photoexcited spin-polarized electrons and holes in a semiconductor recombine by emitting circularly polarized light or the electron spins interact with light and cause a rotation of the light polarization plane) or electronically through charge-spin coupling (when spin accumulates on the conductor side at the interface of a conductor and a ferromagnet, a voltage or a current appears. By measuring the polarity of the voltage or the current, one can predict the spin orientation in the conductor.). In addition, the possibility of having long spin relaxation time or spin diffusion length in electronic materials makes spintronics a viable potential technology.