Shakashakar Open to the public ; QC The tetrahedral and octahedral sites form the two magnetic sublattices, A and B respectively. Separate different tags with antiferromagneyism comma. The magnitude of this magnetization, at 0 K, is dependent on the spin magnetic moments of electrons. Tags What are tags? The strongest superexchange interactions result in an antiparallel alignment of spins between the A and B sublattice. In this case, a paramagnetic correction may be needed.
|Country:||Republic of Macedonia|
|Published (Last):||11 October 2004|
|PDF File Size:||7.4 Mb|
|ePub File Size:||8.7 Mb|
|Price:||Free* [*Free Regsitration Required]|
Measurement[ edit ] When no external field is applied, the antiferromagnetic structure corresponds to a vanishing total magnetization. In an external magnetic field, a kind of ferrimagnetic behavior may be displayed in the antiferromagnetic phase, with the absolute value of one of the sublattice magnetizations differing from that of the other sublattice, resulting in a nonzero net magnetization.
Although the net magnetization should be zero at a temperature of absolute zero , the effect of spin canting often causes a small net magnetization to develop, as seen for example in hematite. In contrast, at the transition between the ferromagnetic to the paramagnetic phases the susceptibility will diverge.
In the antiferromagnetic case, a divergence is observed in the staggered susceptibility. Various microscopic exchange interactions between the magnetic moments or spins may lead to antiferromagnetic structures. In the simplest case, one may consider an Ising model on a bipartite lattice, e. Depending on the sign of that interaction, ferromagnetic or antiferromagnetic order will result. Geometrical frustration or competing ferro- and antiferromagnetic interactions may lead to different and, perhaps, more complicated magnetic structures.
Antiferromagnetic materials[ edit ] Antiferromagnetic structures were first shown through neutron diffraction of transition metal oxides such as nickel, iron, and manganese oxides. The experiments, performed by Clifford Shull , gave the first results showing that magnetic dipoles could be oriented in an antiferromagnetic structure . Antiferromagnetic materials occur commonly among transition metal compounds, especially oxides.
Examples include hematite , metals such as chromium , alloys such as iron manganese FeMn , and oxides such as nickel oxide NiO. There are also numerous examples among high nuclearity metal clusters. Organic molecules can also exhibit antiferromagnetic coupling under rare circumstances, as seen in radicals such as 5-dehydro-m-xylylene.
Antiferromagnets can couple to ferromagnets , for instance, through a mechanism known as exchange bias , in which the ferromagnetic film is either grown upon the antiferromagnet or annealed in an aligning magnetic field, causing the surface atoms of the ferromagnet to align with the surface atoms of the antiferromagnet. This provides the ability to "pin" the orientation of a ferromagnetic film, which provides one of the main uses in so-called spin valves , which are the basis of magnetic sensors including modern hard drive read heads.
Main article: Geometrical frustration Unlike ferromagnetism, anti-ferromagnetic interactions can lead to multiple optimal states ground states—states of minimal energy.
In one dimension, the anti-ferromagnetic ground state is an alternating series of spins: up, down, up, down, etc. Yet in two dimensions, multiple ground states can occur. Consider an equilateral triangle with three spins, one on each vertex. The two situations which are not ground states are when all three spins are up or are all down. In any of the other six states, there will be two favorable interactions and one unfavorable one.
This illustrates frustration : the inability of the system to find a single ground state. This type of magnetic behavior has been found in minerals that have a crystal stacking structure such as a Kagome lattice or hexagonal lattice. Other properties[ edit ] Synthetic antiferromagnets often abbreviated by SAF are artificial antiferromagnets consisting of two or more thin ferromagnetic layers separated by a nonmagnetic layer.
It can only be determined that the average correlation of neighbour spins is antiferromagnetic. This type of magnetism is sometimes called speromagnetism. An interesting phenomenon occurs in anisotropic Heisenberg antiferromagnets in a field, where spin-flop and supersolid phases may be stabilized.
The latter phase has been described first by Takeo Matsubara and H. Matsuda in
Canted Antiferromagnetism: Hematite