Examples of Ferromagnetic and Antiferromagnetic Materials

by **Algerien1970** Sat 13 Jun - 23:09

[size=31] Examples of Ferromagnetic and Antiferromagnetic Materials[/size]

Here is a list of ferromagnetic (including ferrimagnetic) materials (from the "Kittel"). Besides the chemical formula, the[url=http://www.tf.uni-kiel.de/matwis/amat/elmat_en/kap_4/backbone/r4_1_3.html#Curie temperature]Curie temperature[/url] T_C and the [url=http://www.tf.uni-kiel.de/matwis/amat/elmat_en/kap_4/backbone/r4_1_2.html#Magnetic moment]magnetic moment[/url] m_m of the molecules (in units of the [url=http://www.tf.uni-kiel.de/matwis/amat/elmat_en/kap_4/backbone/r4_1_2.html#Bohr magneton]Bohr magneton[/url] m_B) is listed

[th]Material[/th][th]T_C [K][/th][th]m_m[/th]

Fe	1043	2.22
Co	1388	1.72
Ni	627	0.606
Gd	292	7.63
Dy	88	10.2
CrO₂	386	2.03
MnAs	318	3.4
MnBi	630	3.52 + 3.6 Mn –0.15 Bi
EuO	69	6.8
NiO / Fe (Ferrit)	858	2.4
Y₃Fe₅O₁₂	560	5.0

The list could be much longer, but we see a number of interesting facts.

There exist more elemental ferromagnets than just the common trio Fe, Ni, Co - but not at room temperature!

Elements that do not form a ferromagnetic elemental crystal, may become from ferromagnetic crystals in combination with some other atoms. This is especially true for Mn and Cr compounds.

There are many "strange" oxides or mixtures of oxides of non-magnetic elements (EuO) or magnetic elements that are ferri- or ferromagnetic. Most compounds with the composition MOFe₂O₃ and M being some bivalent metal (including Fe) are ferrimagnets.

The total magnetic moment carried by the atoms or molecules can be rather large; it is a combination of the moments of the atoms (and, if applicable, whatever free electrons contribute). It is constructed from positive and negative contributions for ferrimagnets (as shown for the MnBi case), It is, however not obvious, if the total magnetic moment from some compound is "ferro" (all contributions same direction or sign) or "ferri" (different signs). While most oxides are "ferro", some (e.g. CrBr₃, EuO, EuS) are "ferro".

Here is a list of anti-ferromagnetic materials; T_N is now the [url=http://www.tf.uni-kiel.de/matwis/amat/elmat_en/kap_4/backbone/r4_1_3.html#Neel temperature]Néel temperature[/url]

[th]Material[/th][th]T_N [K][/th]

Cr	308
MnO	116
MnS	160
NiO	525
FeCl₂	24
FeO	198
CoCl₂	25
CoO	291
NiCl₂	50
NiO	525

We find the by now usual suspects Fe, Ni, Co, Mn, Cr and their oxides, but also plenty of other compounds (mostly not listed).

While anti-ferromagnetic ordering provides endless challenges for solid state physicists, it appears that there are no practical uses for this magnetic property at present.