Antiferromagnetism and Ferrimagnetism

The formula for Fe304 may be written as Fe O -(Fe )2(0 )3, in which the Fe ions exist in both +2 and -1-3 valence states in the ratio of 1 2. A net spin magnetic moment exists for each Fe and Fe ion, which corresponds to 4 and 5 Bohr magnetons, respectively, for the two ion types. Furthermore, the 0 ions are magnetically neutral. There are antiparallel spin-coupling interactions between the Fe ions, similar in character to antiferromagnetism. However, the net ferrimagnetic moment arises from the incomplete cancellation of spin moments. 

Cubic ferrites have the inverse spinel crystal structure, which is cubic in symmetry and is similar to the spinel structure (Section 12.2). The inverse spinel crystal structure might be thought of as having been generated by the stacking of close-packed planes 

Cubic ferrites having other compositions may be produced by adding metallic ions that substitute for some of the iron in the crystal structure. Again, from the ferrite chemical formula M 0 -(Fe )2(0 )3, in addition to Fe , may represent 

The Distribution of Spin Magnetic Momenb for Fe and Fe Ions in a Unit Cell of Fe304  

Cation Octahedral Lattice Site Tetrahedral Lattice Site Net Magnetic Moment 

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The development of neutron diffraction by C G Shull and coworkers [30] led to the detennination of the existence, previously only a hypothesis, of antiferromagnetism and ferrimagnetism. More recently neutron diffraction, because of its sensitivity to light elements in the presence of heavy ones, played a cmcial role in demonstrating the importance of oxygen content m high-temperature superconductors. 

H. Alfven (Stockholm) discoveries in magneto-hydrodynamics with fruitful applications in different parts of plasma physics. L. Neel (Grenoble) discoveries concerning antiferromagnetism and ferrimagnetism which have led to important applications in solid state physics. 

There are several types of magnetic behaviour that affect the specific heat of a material paramagnetism, ferromagnetism, antiferromagnetism and ferrimagnetism. Diamagnetism, being independent of temperature, causes no specific heat contribution and is not considered. 

Williams and Chamberland (140) discussed the application of DSC to the determination of Curie temperatures of ferromagnetic materials and Neel temperatures of antiferromagnetic and ferrimagnetic materials. 

Fig. 6.4 Mossbauer spectra of RbFeFs in the paramagnetic, antiferromagnetic, and ferrimagnetic regions. [Ref. 11, Fig. 3]...

FIGURE 33.11 Schematic comparing dipole alignments in ferromagnetic, antiferromagnetic, and ferrimagnetic materials. 

Long-range order ferromagnetism, antiferromagnetism and ferrimagnetism... 

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