ELECTROMAGNETIC STATES OF MATERIALS

Note: Some of the descriptions below are excerpts from Wikipedia and most of these descriptions have links to external web pages giving more information on the electromagnetic state.

Diamagnetic

http://en.wikipedia.org/wiki/Diamagnetic
Diamagnetism is the property of an object which causes it to create a magnetic field in opposition of an externally applied magnetic field, thus causing a repulsive effect. Diamagnetism is a form of magnetism that is only exhibited by a substance in the presence of an externally applied magnetic field. It is generally a quite weak effect in most materials, although superconductors exhibit a strong effect.

All materials show a diamagnetic response in an applied magnetic field. In fact, diamagnetism is a very general phenomenon, because all paired electrons, including the core electrons of an atom, will always make a weak diamagnetic contribution to the material's response. However, for materials that show some other form of magnetism (such as ferromagnetism or paramagnetism), the diamagnetism is completely overpowered. Substances that mostly display diamagnetic behaviour are termed diamagnetic materials, or diamagnets. Materials that are said to be diamagnetic are those that are usually considered by non-physicists to be "non-magnetic", and include water, wood, most organic compounds such as petroleum and some plastics, and many metals including copper, particularly the heavy ones with many core electrons, such as mercury, gold and bismuth.

Diamagnetic materials have a relative magnetic permeability that is less than 1, thus a magnetic susceptibility which is less than 0, and are therefore repelled by magnetic fields. However, since diamagnetism is such a weak property its effects are not observable in every-day life. Their values are orders of magnitudes smaller than the magnetism exhibited by paramagnets and ferromagnets.

Additionally, all conductors exhibit an effective diamagnetism when they move through a magnetic field. The Lorentz force on electrons causes them to circulate around forming eddy currents. The eddy currents then produce an induced magnetic field which opposes the applied field, resisting the conductor's motion.

Diamagnetism in common materials
Bismuth -16.6
Carbon (diamond) -2.1
Carbon (graphite) -1.6
Copper -1.0
Lead -1.8
Mercury -2.9
Silver -2.6
Water -0.91

Ferromagnetic

http://en.wikipedia.org/wiki/Ferromagnetic
Ferromagnetism is the basic mechanism by which certain materials (such as iron) form permanent magnets and/or exhibit strong interactions with magnets; it's responsible for most phenomena of magnetism encountered in everyday life.

All permanent magnets (materials that can be magnetized by an external magnetic field and which remain magnetized after the external field is removed) are either ferromagnetic or ferrimagnetic, as are the metals that are noticeably attracted to them.

To distinguish it from ferrimagnetism, a material is "ferromagnetic" in this narrower sense only if all of its magnetic ions add a positive contribution to the net magnetization. If some of the magnetic ions subtract from the net magnetization (if they are partially anti-aligned), then the material is "ferrimagnetic". If the ions anti-align completely so as to have zero net magnetization, despite the magnetic ordering, then it's an antiferromagnet

A selection of crystalline ferromagnetic (* = ferrimagnetic) materials, along with their Curie temperatures in kelvins (K).
Co 1388
Fe 1043
FeOFe2O3* 858
NiOFe2O3* 858
CuOFe2O3* 728
MgOFe2O3* 713
MnBi 630
Ni 627
MnSb 587
MnOFe2O3* 573
Y3Fe5O12* 560
CrO2 386
MnAs 318
Gd 292

Ferrimagnetic

http://en.wikipedia.org/wiki/Ferrimagnetism
A ferrimagnetic material is one in which the magnetic moment of the atoms on different sublattices are opposed, as in antiferromagnetism; however, in ferrimagnetic materials, the opposing moments are unequal and a spontaneous magnetization remains. This happens when the sublattices consist of different materials or ions (such as Fe2+ and Fe3+)

Ferrimagnetism is exhibited by ferrites and magnetic garnets. The oldest-known magnetic substance, magnetite, is a ferrimagnet; it was originally classified as a ferromagnet before Néel's discovery of ferrimagnetism and antiferromagnetism.

Some ferrimagnetic materials are YIG (yttrium iron garnet) and ferrites composed of iron oxides and other elements such as aluminum, cobalt, nickel, manganese and zinc.

Ferrimagnetic materials have high resistivity and have anisotropic properties. The anisotropy is actually induced by an external applied field. When this applied field aligns with the magnetic dipoles it causes a net magnetic dipole moment and causes the magnetic dipoles to precess at a frequency controlled by the applied field, called Larmor or precession frequency.

Antiferromagnetic

http://en.wikipedia.org/wiki/Antiferromagnetism
In materials that exhibit antiferromagnetism, the magnetic moments of atoms or molecules, usually related to the spins of electrons, align in a regular pattern with neighboring spins (on different sublattices) pointing in opposite directions. When no external field is applied, the antiferromagnetic structure corresponds to a vanishing total magnetization. In a field, a kind of ferrimagnetic behavior may be displayed in the antiferromagnetic phase, with the absolute value of one of the sublattice magnetizations differing from that of the other sublattice, resulting in a nonzero net magnetization. Antiferromagnetic materials occur less frequently in nature than ferromagnetic ones. Better known examples include hematite, metals such as chromium, alloys such as iron manganese (FeMn), and oxides such as nickel oxide (NiO).

Paramagnetic

http://en.wikipedia.org/wiki/Paramagnetic
Paramagnetism is a form of magnetism which occurs only in the presence of an externally applied magnetic field. Paramagnetic materials are attracted to magnetic fields, hence have a relative magnetic permeability greater than one (or, equivalently, a positive magnetic susceptibility). The force of attraction generated by the applied field is linear in the field strength and rather weak. It typically requires a sensitive analytical balance to detect the effect. Unlike ferromagnets, paramagnets do not retain any magnetization in the absence of an externally applied magnetic field, because thermal motion causes the spins to become randomly oriented without it. Thus the total magnetization will drop to zero when the applied field is removed. Even in the presence of the field there is only a small induced magnetization because only a small fraction of the spins will be oriented by the field. This fraction is proportional to the field strength and this explains the linear dependency. The attraction experienced by ferromagnets is non-linear and much stronger, so that it's easily observed, for instance, in magnets on one's refrigerator.

Paramagnetism in common materials
Iron oxide 720
Uranium 40
Platinum 26
Tungsten 6.8
Cesium 5.1
Aluminum 2.2
Lithium 1.4
Magnesium 1.2
Sodium 0.72
Oxygen 0.19

Dielectric

A dielectric is a material that does not conduct electrical current. The term is generally used for non conduction of alternating current while insulator is generally used for material being used to withstand a high electric field.

Electret

http://en.wikipedia.org/wiki/Electret
Electret is a dielectric material that has a quasi-permanent electric charge or dipole polarisation. An electret generates internal and external electric fields, and is the electrostatic equivalent of a permanent magnet.

There is a similarity between electrets and the dielectric layer used in capacitors; the difference is that dielectrics in capacitors possess an induced polarization that is only transient, dependent on the potential applied on the dielectric, while dielectrics with electret properties exhibit quasi-permanent charge storage or dipole polarization in addition. Some materials also display ferroelectricity; i.e. they react to the external fields with a hysteresis of the polarization; ferroelectrics can retain the polarization permanently because they are in thermodynamic equilibrium, and are used in ferroelectric capacitors.

Electret materials are quite common in nature. Quartz and other forms of silicon dioxide, for example, are naturally occurring electrets. An electret is a stable dielectric material with a permanently-embedded static electric charge (which, due to the high resistance of the material, will not decay for hundreds of years).

Ferroelectrics

http://en.wikipedia.org/wiki/Ferroelectric
Ferroelectricity is a spontaneous electric polarization of a material that can be reversed by the application of an external electric field. The spontaneous polarization of ferroelectric materials implies a hysteresis effect. All ferroelectrics are required by symmetry considerations to be also piezoelectric and pyroelectric.

Other States

The following are other Magnetic States of materials that not likely to be encountered within the operation of humanitarian demining

Superdiamagnetism
Superparamagnetism
metamagnetism
spin glass
ferromagnetic superconductor

There are also a number of other electric states of material which haven't been researched as to whether any of them are of interest for characterising underground anomalies.