Ferromagnetism

Ferromagnetism is a phenomenon by which a material can exhibit a spontaneous magnetization, and is one of the strongest forms of magnetism. It is responsible for most of the magnetic behavior encountered in everyday life and, along with ferrimagnetism, is the basis for all permanent magnets (as well as the metals that are noticeably attracted to them).

Ferromagnetic materials

~ ~ ~ ~ ~ ~ ~ ~ ~ ~

MaterialCurie temp. (K)

~ ~ ~ ~ ~ ~ ~ ~ ~ ~

Co1388

~ ~ ~ ~ ~ ~ ~ ~ ~ ~

Fe1043

~ ~ ~ ~ ~ ~ ~ ~ ~ ~

FeOFe2O3858

~ ~ ~ ~ ~ ~ ~ ~ ~ ~

NiOFe2O3858

~ ~ ~ ~ ~ ~ ~ ~ ~ ~

CuOFe2O3728

~ ~ ~ ~ ~ ~ ~ ~ ~ ~

MgOFe2O3713

~ ~ ~ ~ ~ ~ ~ ~ ~ ~

MnBi630

~ ~ ~ ~ ~ ~ ~ ~ ~ ~

Ni627

~ ~ ~ ~ ~ ~ ~ ~ ~ ~

MnSb587

~ ~ ~ ~ ~ ~ ~ ~ ~ ~

MnOFe2O3573

~ ~ ~ ~ ~ ~ ~ ~ ~ ~

Y3Fe5O12560

~ ~ ~ ~ ~ ~ ~ ~ ~ ~

CrO2386

Related Topics:
Cr - O

~ ~ ~ ~ ~ ~ ~ ~ ~ ~

MnAs318

Related Topics:
Mn - As

~ ~ ~ ~ ~ ~ ~ ~ ~ ~

Gd292

~ ~ ~ ~ ~ ~ ~ ~ ~ ~

Dy88

~ ~ ~ ~ ~ ~ ~ ~ ~ ~

EuO69

~ ~ ~ ~ ~ ~ ~ ~ ~ ~

~ ~ ~ ~ ~ ~ ~ ~ ~ ~

A selection of crystalline ferromagnetic materials, along with their Curie temperatures in kelvins (K). (Kittel, p. 449.)

~ ~ ~ ~ ~ ~ ~ ~ ~ ~

~ ~ ~ ~ ~ ~ ~ ~ ~ ~

There are a number of crystalline materials that exhibit ferromagnetism. The table, at right, lists a representative selection of them here, along with their Curie temperatures, the temperature above which they cease to be ferromagnetic (see below).

~ ~ ~ ~ ~ ~ ~ ~ ~ ~

Ferromagnetic metal alloys whose constituents are not themselves ferromagnetic in their pure forms are called Heusler alloys, named after Fritz Heusler (1903).

Related Topics:
Heusler alloy - Fritz Heusler

~ ~ ~ ~ ~ ~ ~ ~ ~ ~

One can also make amorphous (non-crystalline) ferromagnetic metallic alloys by very rapid quenching (cooling) of a liquid alloy. These have the advantage that their properties are nearly isotropic (not aligned along a crystal axis); this results in low coercivity, low hysteresis loss, high permeability, and high electrical resistivity. A typical such material is a transition metal-metalloid alloy, made from about 80% transition metal (usually Fe, Co, or Ni) and a metalloid component (B, C, Si, P, or Al) that lowers the melting point.

Related Topics:
Hysteresis - B - C - Si - P - Al

~ ~ ~ ~ ~ ~ ~ ~ ~ ~

One example of such an amorphous alloy is Fe80B20 (Metglas 2605) which has a Curie temperature of 647 K and a room-temperature (300 K) saturation magnetization of 125.7 milliteslas (1257 gauss), compared with 1043 K and 170.7 mT (1707 gauss) for pure iron from above. The melting point, or more precisely the glass transition temperature, is only 714 K for the alloy versus 1811 K for pure iron.

Related Topics:
Milliteslas - Gauss

~ ~ ~ ~ ~ ~ ~ ~ ~ ~