Magnetic materials today constitute, from the standpoint of
the size of their world market and in the narrow concurrence
with the semiconducting materials, one of the major groups
of functional materials. They are involved in a broad range
of technologies, from electromechanics to those related to
information recording. Although it is difficult to find a common
point underlying this large set of applications and
devices, the occurrence of hysteresis in their response to an
applied magnetic field could be considered the most representative
feature of the magnetic materials phenomenology.
Magnetic hysteresis can be described by two quantities,
namely, the remanence and the coercive force. For a given
set of phases, present in a particular material and characterized
by particular values of saturation magnetization,
order temperature, and magnetocrystalline anisotropies, the
coercivity and remanence depend on many different extrinsic
parameters, from the phase morphology (crystallites size
and shape) to the distribution of defects present in them
and, particularly, the characteristics of the intergranular and
interphase couplings. The basic consequences of this are the
possibility of optimizing and, in some cases, tailoring the
properties of a material for a particular application, during
the last century, most of the research efforts in the field
were concentrated on the control of the micro- and nanostructures
of a relatively reduced set of relevant phases. It
also is important to state that, whereas the coercivity of the
technologically used magnetic materials covers six decades
(from ca. 5×10−6 T up to ca. 5 T), the remanence values are
bound by the value of the saturation magnetization, and the
whole range of technologically relevant magnetic materials
varies from 0.5 T up to ca. 2 T.