Biomedical Engineering Reference
In-Depth Information
13.1.3.2.3 Domain Structure and Hysteresis Loop
Materials that exhibit both magnetic and electrical ordering have become
a hot topic of research in recent years. h e link between magnetic and elec-
tric properties potentially allows the creation of novel devices if magnetic
and electric order can be mutually controlled. h e Maxwell equations that
relate electric and magnetic i elds, charge density and current density show
that magnetic and electric interactions couple to each other. h e formal
equivalence of the equations of electrostatics and magnetostatics explains
numerous similarities in the theory of ferroelectrics and ferromagnets, for
instance, their behavior in external i elds. Switching of electric and mag-
netic domains is associated with a hysteresis loop since it can be assimilated
to an isothermal/isostructural i rst-order phase transition (Figure 13.5).
13.1.3.2.4 Applications of Multiferroics
Multiferroic materials are a very important class of materials because of the
coupling between the magnetic i eld and electric polarization, which make
them very useful for magnetic sensors with high transduction ei ciency
between the magnetic and electric energies. Multiferroic composite struc-
tures in bulk form are explored for high-sensitivity ac magnetic i eld sen-
sors and electrically tunable microwave devices such as i lters, oscillators and
phase shit ers (in which the ferri-, ferro- or antiferro-magnetic resonance is
tuned electrically instead of magnetically) [21]. In multiferroic thin i lms,
the coupled magnetic and ferroelectric order parameters can be exploited
Ferroelectric
Ferromagnetic
Ferrotoroidic
Ferroelastic
Figure 13.5
Domain switching and hysteresis cycles of the four primary ferroics. h e
symmetry symbol used for the toroidal moment corresponds to the co-axial mirror
plane cross-section of a toroid with an even number of windings (see inset). Note that for
certain symmetries, a toroidal moment cannot only be switched by (
E
×
H
)i
, but also by
collinear electric and magnetic i elds or by a magnetic i eld alone.
