Ferrimagnets

Ferrimagnets are materials in which the magnetic moments of atoms on different sublattices are aligned antiparallel, but with unequal magnitudes, resulting in a nonzero net magnetization in the ordered state. This contrasts with ferromagnets, where moments align parallel, and antiferromagnets, where the net moment vanishes due to equal opposite sublattice moments.

The magnetic order is produced by exchange interactions between ions on different lattice sites, often in oxide compounds with iron group elements. Common structures include spinels with formula AB2O4 and garnets such as Y3Fe5O12, as well as magnetite Fe3O4. In ferrites, a divalent metal ion (for example Ni2+, Zn2+) occupies one sublattice, while Fe3+ occupies others, leading to a net moment.

Properties of ferrimagnets include typically high magnetic permeability and, in many cases, notable coercivity. They also often exhibit high electrical resistivity, which reduces eddy currents at high frequencies. The temperature dependence of the sublattice magnetizations can produce a compensation point, at which the net magnetization vanishes while magnetic order persists; above the Curie temperature, long-range ferrimagnetic order disappears.

Applications include soft ferrites used in transformer cores, inductors, and high-frequency devices; garnets like yttrium iron garnet (YIG) are important in microwave technology and magnonics; ferrimagnetic materials are also used in magnetic recording media and spintronic components.