ABSTRACT
CONTENTS 4.1 Introduction ....................................................................................................................... 101 4.2 Diamagnetic Materials ..................................................................................................... 102 4.3 Paramagnetic Materials ................................................................................................... 102 4.4 Ferromagnetic Materials .................................................................................................. 103
4.4.1 Antiferromagnetism............................................................................................. 104 4.4.2 Ferrimagnetism ..................................................................................................... 105 4.4.3 Temperature Dependence of Ferromagnetism................................................ 105
4.5 Biological Magnets............................................................................................................ 106 4.6 Magnetic Iron Compounds Related to Pathogenesis.................................................. 109 References ................................................................................................................................... 111
Magnetism arises from the movement of electrical charges, such as the oscillation of electrons in a conducting wire, the flow of ions in an organism or the orbital, and spin motions of electrons in an atom. Since all materials contain moving subatomic particles (electrons and protons), all materials are, in some sense, ‘‘magnetic.’’ In order to understand more about the role of magnetic materials in organisms, it is first necessary to examine what is meant by the various types of magnetic behavior of materials. The magnetic properties of materials are dominated by the electron spin motion. In
quantum mechanical terms, electrons may assume two possible spin states: spin þ1/2 or spin 1/2. These may also be referred to as ‘‘spin up’’ and ‘‘spin down.’’ The Pauli exclusion principle states that no two electrons may occupy the same energy state in an atom. This means that no two electrons may have the same set of values for the quantum numbers as they would then be indistinguishable. As electrons are added, they fill up each possible state in a given shell before filling the shell associated with the next higher energy state. The filling of the shells is governed by Schro¨dinger’s wave equation and the quantum numbers. Electrons are added to subshells in parallel spin configurations first according to
Hund’s rule. If all electrons are paired, there is no ‘‘spin’’ magnetic moment. These materials are still magnetic though, because of the electron’s orbital motion. In most materials of biological origin, however, electron spin motion is cancelled, allowing electron orbital motion to dominate.
