Ferrimagnetic garnets

(materials) A synthetic ferrimagnetic oxide material that has the garnet structure and the chemical formula X₃Fe₅O₁₂, where the trivalent X ion is yttrium, or any of the rare-earth ions with an atomic number greater than 61.

A class of ferrimagnetic oxide materials that have the garnet crystal structure. The typical formula of a ferrimagnetic garnet is X₃Fe₅O₁₂, where the trivalent X ion is yttrium, or any of the rare-earth ions with an atomic number greater than 61. (The rare-earth ions below samarium apparently have radii too large to fit into the garnet structure.) However, the larger rare earths and lanthanum can substitute partially for some of the yttrium or smaller rare earths. See also Ferrimagnetism; Ferrite; Rare-earth elements.

Ferrimagnetic garnets are of great theoretical interest because they have a highly ordered structure and because they accommodate rare-earth ions, some of which have a small contribution to their magnetism due to the orbital motion of electrons, in addition to the magnetism due to electron spin. The first practical engineering interest in the ferrimagnetic garnets was due to the yttrium iron garnet, which is used in certain microwave ferrite devices because of its very narrow ferromagnetic resonance absorption line. Development of magnetic bubbles for use in solid-state nonvolatile memory devices resulted in a large research effort on complex rare-earth iron garnets. In these garnets several different rare-earth ions are simultaneously incorporated in the structure in concentrations designed to optimize a number of physical and magnetic properties which influence the memory parameters. See also Computer storage technology; Ferrite devices; Gyrator.