Ferromagnetic Material

ferromagnetic material

[¦fe·rō·mag¦ned·ik mə′tir·ē·əl] (solid-state physics) A material displaying ferromagnetism, such as the various forms of iron, steel, cobalt, nickel, and their alloys.

Ferromagnetic Material

 

any one of the substances (generally in the solid crystalline state) in which ferromagnetic ordering of the magnetic moments of atoms or ions (in nonmetallic crystals) or of the moments of conduction electrons (in metallic crystals) occurs below a certain temperature (Curie point θ). Of the chemical elements, the transition elements Fe, Co, and Ni (unfilled 3d orbitals) and the rare-earth metals Gd, Tb, Dy, Ho, and Erare ferromagnetic (Table 1).

Table 1. Ferromagnetic metals
 θ,°KJs0, gauss1
1Js0 is the magnetization per unit volume at absolute zero
Fe ...............10431,735.2
Co ...............14031,445
Ni ...............631508.8
Gd ...............2891,980
Tb ...............2232,713
Dy ...............871,991.8
Ho ...............203,054.6
Er ...............19.61,872.6

A collinear ferromagnetic atomic structure is characteristic of Gd and the metals with unfilled 3d orbitals; the structure of the other rare-earth ferromagnetic materials is not collinear and in some cases is helical. Numerous metallic binary and complex (multicomponent) alloys are ferromagnetic, as are compounds that the above metals form with one another and with other non-ferromagnetic elements. Alloys and compounds of Cr and Mn with nonferromagnetic elements (Heusler alloys) are also ferromagnetic. Other ferromagnetic materials include the compounds ZrZn2 and ZrxM,l–x Zn2 (where M is Ti, Y, Nb, or Hf; 0 ≤ x ≤ 1), Au4V, Sc3In (Table 2), and certain compounds, such as UH3, formed by metals of the actinide series.

Table 2. Ferromagnetic compounds
 θ,°K
Fe3Al ...............743
Ni3Mn ...............773
FePd3 ...............705
MnPt3 ...............350
CrPt3 ...............580
ZnCMn3 ...............353
AlCMn3 ...............275
TbN ...............43
DyN ...............26
EuO ...............77
MnB ...............578
ZrZn2 ...............35
Au4V ...............42–43
Sc3ln ...............5–6

Heavily diluted substitution solid solutions of such paramagnetic atoms as Fe or Co in a diamagnetic matrix of Pd form a special group of ferromagnetic materials. In these substances, the atomic magnetic moments are randomly distributed; that is, there is magnetic order in the absence of atomic order. Magnetic ordering also has been detected in amorphous (metastable) metallic alloys and compounds, amorphous semiconductors, ordinary organic and inorganic glasses, and chalcogenides (sulfides, selenides, tellurides). Only a small number of nonmetallic ferromagnetic materials are known. They include ionic compounds of the type La1–xCaxMnO5 (0.4 > x > 0.2), EuO, Eu2SiO4, EuS, EuSe, EuI2, and CrB3. In most of these substances, the Curie point lies below 1°K. Only in compounds of Eu, in the chalcogenides, and in CrB3 is the value of θ ~ 100°K.

S. V. VONSOVSKII