Magnetism in which the moments of two antiparallel sublattices differ in size, leaving a spontaneous magnetization equal to the difference. Ferrites such as magnetite are typical examples.
Japanese name: フェリ磁性
Ferrimagnetism appears in 1 practice question across 1 topic, including Magnetic materials.
Field: Magnetic materials
Ferrimagnetism is magnetism in which moments on two kinds of sites in a crystal (sublattices) align antiparallel, leaving a spontaneous magnetization equal to the difference in their sizes. Magnetic oxides such as magnetite had long been known as magnets, but the fact that their magnetization is much smaller than that of ferromagnetic metals was first explained by this idea. The Frenchman Néel set out the theory in 1948, and for this work together with that on antiferromagnetism he received the Nobel Prize in Physics in 1970. In oxides, superexchange through the oxygen ions between metal ions acts to align the moments antiparallel.
The magnetizations of the two sublattices decrease differently with temperature, so the temperature dependence of the total magnetization can take shapes unlike those of ferromagnets. In some rare-earth iron garnets, one sublattice dominates at low temperature and the other at high temperature, and in between a compensation temperature appears where the two cancel and the magnetization is 0; for gadolinium iron garnet it lies near room temperature. The temperature at which the spontaneous magnetization vanishes is called the Curie temperature and is about 580°C for magnetite. Another feature is that in the paramagnetic range above it, the inverse susceptibility plotted against temperature is not a straight line but a curve.
Seen from outside, ferrimagnets closely resemble ferromagnets: they have domains, show hysteresis and stick to magnets. To tell them apart, the orientation of the moments on each sublattice is examined by neutron diffraction, or the saturation magnetization is compared with the sum of the atomic moments. That the measured saturation magnetization of magnetite Fe₃O₄ is about 4 µB per formula unit, far smaller than the sum of the moments of three iron ions, is typical evidence of ferrimagnetism. In antiferromagnetism the moments of the two sublattices are equal and cancel completely, so no spontaneous magnetization remains.
The typical ferrimagnetic materials are ferrites, including the spinel type MFe₂O₄, the magnetoplumbite (hexagonal) types BaFe₁₂O₁₉ and SrFe₁₂O₁₉, and the garnet type Y₃Fe₅O₁₂. Being oxides, their electrical resistivity is orders of magnitude higher than that of metals and eddy currents hardly flow even at high frequencies, so Mn-Zn and Ni-Zn spinel ferrites are used in transformers for switching power supplies and in parts for noise suppression. Hexagonal ferrites have large magnetocrystalline anisotropy and are used in huge quantities in motors and elsewhere as cheap permanent magnets that do not rust, and garnets are used in microwave devices.
Answer: C. The moments of two sublattices are aligned antiparallel but differ in size, so they do not cancel and a spontaneous magnetization remains
In a ferrimagnet, the magnetic moments on two kinds of sites in the crystal (sublattices) are aligned antiparallel to each other by the exchange interaction. Because the moments on the two sublattices differ in size or number, they do not cancel completely, and a spontaneous magnetization equal to the difference remains. Macroscopically a ferrimagnet shows domains and hysteresis just as a ferromagnet does, but its saturation magnetization is smaller than that of ferromagnetic metals such as iron. Parallel alignment of all moments is ferromagnetism, and antiparallel moments of equal size that cancel is antiferromagnetism. Ferrites are oxides with a high electrical resistivity, so eddy currents hardly flow in them, and they are used as cores at high frequencies.
No. Ferrite in magnetic materials is the general name for iron oxides that show ferrimagnetism. Ferrite in steel is the name of the microstructure of body-centered cubic iron (α-iron) and its solid solutions, which is ferromagnetic. The name is the same, but the substance and the type of magnetism are different.
Because the moments of the two sublattices align antiparallel and only the difference remains. In oxides, moreover, oxygen ions with no magnetic moment occupy much of the volume, so there is less moment per unit volume as well. The saturation flux density of ferrites is therefore around 0.5 T, smaller than the roughly 2.2 T of iron.
In a ferrimagnet whose two sublattice magnetizations change differently with temperature, it is the temperature at which their sizes are exactly equal and the total magnetization is 0. Above and below it, the sublattice that sets the direction of the total magnetization switches. Materials for magneto-optical recording made use of properties near this temperature.
In a ferrimagnet, the magnetic moments on two kinds of sites in the crystal (sublattices) are aligned antiparallel to each other by the exchange interaction.
Which statement correctly describes the ferrimagnetism show…Magnetic domain Saturation magnetization Domain wall Eddy-current loss Magnetocrystalline anisotropy Maximum energy product Superparamagnetism