Orthoferrite
Encyclopedia
An orthoferrite is any of a class of chemical compound
s with the formula RFeO (where R is one or more rare-earth elements). Orthoferrites have an orthorhombic crystal structure with a space group Pbnm and most are weakly ferromagnetic.
At the Néel temperature
TN the subsystem of iron ions orders into a slightly canted antiferromagnetic structure with antiferromagnetic moment G and a weak ferromagnetic moment F. The rare-earth ion subsystem acquires magnetization m due to an interaction with the iron subsystem.
The orthoferrites are particularly interesting because of the presence of an antisymmetric exchange interaction which involves the vector cross product of neighboring spins as opposed to the usual scalar product. In the absence of this interaction, the orthoferrites would be antiferromagnetic. Its presence leads to a small canting of the sublattices, making the orthoferrites “weak” ferromagnets with 4πMs = 100 G. Another interesting feature of these materials is the fact that some of them exhibit a transition as a function of temperature, in which the direction of the antiferromagnetically ordered spins and consequently also of the net magnetization rotates by 90°.
Orthoferrites are transparent, and can modify the polarisation of a beam of light
under the control of a magnetic field
(Faraday rotation). This makes them potentially useful as optical sensors and actuators for use in optical communications.
They were also once used as the magnetic material in bubble memory
.
Chemical compound
A chemical compound is a pure chemical substance consisting of two or more different chemical elements that can be separated into simpler substances by chemical reactions. Chemical compounds have a unique and defined chemical structure; they consist of a fixed ratio of atoms that are held together...
s with the formula RFeO (where R is one or more rare-earth elements). Orthoferrites have an orthorhombic crystal structure with a space group Pbnm and most are weakly ferromagnetic.
At the Néel temperature
Néel temperature
The Néel temperature or magnetic ordering temperature , TN, is the temperature above which an antiferromagnetic material becomes paramagnetic—that is, the thermal energy becomes large enough to destroy the macroscopic magnetic ordering within the material....
TN the subsystem of iron ions orders into a slightly canted antiferromagnetic structure with antiferromagnetic moment G and a weak ferromagnetic moment F. The rare-earth ion subsystem acquires magnetization m due to an interaction with the iron subsystem.
The orthoferrites are particularly interesting because of the presence of an antisymmetric exchange interaction which involves the vector cross product of neighboring spins as opposed to the usual scalar product. In the absence of this interaction, the orthoferrites would be antiferromagnetic. Its presence leads to a small canting of the sublattices, making the orthoferrites “weak” ferromagnets with 4πMs = 100 G. Another interesting feature of these materials is the fact that some of them exhibit a transition as a function of temperature, in which the direction of the antiferromagnetically ordered spins and consequently also of the net magnetization rotates by 90°.
Applications
The combination of high magnetic resonance frequencies with very large magnetooptical effects makes the orthoferrites interesting objects for study of laser-induced dynamics.Orthoferrites are transparent, and can modify the polarisation of a beam of light
Light
Light or visible light is electromagnetic radiation that is visible to the human eye, and is responsible for the sense of sight. Visible light has wavelength in a range from about 380 nanometres to about 740 nm, with a frequency range of about 405 THz to 790 THz...
under the control of a magnetic field
Magnetic field
A magnetic field is a mathematical description of the magnetic influence of electric currents and magnetic materials. The magnetic field at any given point is specified by both a direction and a magnitude ; as such it is a vector field.Technically, a magnetic field is a pseudo vector;...
(Faraday rotation). This makes them potentially useful as optical sensors and actuators for use in optical communications.
They were also once used as the magnetic material in bubble memory
Bubble memory
Bubble memory is a type of non-volatile computer memory that uses a thin film of a magnetic material to hold small magnetized areas, known as bubbles or domains, each storing one bit of data...
.
Examples
- LanthanumLanthanumLanthanum is a chemical element with the symbol La and atomic number 57.Lanthanum is a silvery white metallic element that belongs to group 3 of the periodic table and is the first element of the lanthanide series. It is found in some rare-earth minerals, usually in combination with cerium and...
orthoferrite, LaFeO - DysprosiumDysprosiumDysprosium is a chemical element with the symbol Dy and atomic number 66. It is a rare earth element with a metallic silver luster. Dysprosium is never found in nature as a free element, though it is found in various minerals, such as xenotime...
orthoferrite, DyFeO