Rare earth magneto optical materials
Magneto optical materials refer to optical information functional materials with magneto optical effects in the ultraviolet to infrared bands. Rare earth magneto optical materials are a new type of optical information functional materials that can be made into optical devices with various functions by utilizing their magneto optical properties and the interaction and conversion of light, electricity, and magnetism. Such as modulators, isolators, circulators, magneto-optical switches, deflectors, phase shifters, optical information processors, displays, memories, laser gyro bias mirrors, magnetometers, magneto-optical sensors, printing machines, video recorders, pattern recognition machines, optical discs, optical waveguides, etc.
The Source of Rare Earth Magneto Optics
The rare earth element generates an uncorrected magnetic moment due to the unfilled 4f electron layer, which is the source of strong magnetism; At the same time, it can also lead to electron transitions, which is the cause of light excitation, leading to strong magneto optical effects.
Pure rare earth metals do not exhibit strong magneto optical effects. Only when rare earth elements are doped into optical materials such as glass, compound crystals, and alloy films, will the strong magneto-optical effect of rare earth elements appear. The commonly used magneto-optical materials are transition group elements such as (REBi) 3 (FeA) 5O12 garnet crystals (metal elements such as A1, Ga, Sc, Ge, In), RETM amorphous films (Fe, Co, Ni, Mn), and rare earth glasses.
Magneto optical crystal
Magneto optic crystals are crystal materials with magneto optic effects. The magneto-optical effect is closely related to the magnetism of crystal materials, especially the magnetization strength of the materials. Therefore, some excellent magnetic materials are often magneto-optical materials with excellent magneto-optical properties, such as yttrium iron garnet and rare earth iron garnet crystals. Generally speaking, crystals with better magneto-optical properties are ferromagnetic and ferrimagnetic crystals, such as EuO and EuS being ferromagnets, yttrium iron garnet and bismuth doped rare earth iron garnet being ferrimagnets. At present, these two types of crystals are mainly used, especially ferrous magnetic crystals.
Rare earth iron garnet magneto-optical material
1. Structural characteristics of rare earth iron garnet magneto-optical materials
Garnet type ferrite materials are a new type of magnetic materials that have rapidly developed in modern times. The most important of them is rare earth iron garnet (also known as magnetic garnet), commonly referred to as RE3Fe2Fe3O12 (can be abbreviated as RE3Fe5O12), where RE is a yttrium ion (some are also doped with Ca, Bi plasma), Fe ions in Fe2 can be replaced by In, Se, Cr plasma, and Fe ions in Fe can be replaced by A, Ga plasma. There are a total of 11 types of single rare earth iron garnet that have been produced so far, with the most typical being Y3Fe5O12, abbreviated as YIG.
2. Yttrium iron garnet magneto-optical material
Yttrium iron garnet (YIG) was first discovered by Bell Corporation in 1956 as a single crystal with strong magneto-optical effects. Magnetized yttrium iron garnet (YIG) has a magnetic loss several orders of magnitude lower than any other ferrite in the ultra-high frequency field, making it widely used as an information storage material.
3. High Doped Bi Series Rare Earth Iron Garnet Magneto Optical Materials
With the development of optical communication technology, the requirements for information transmission quality and capacity have also increased. From the perspective of material research, it is necessary to improve the performance of magneto-optical materials as the core of isolators, so that their Faraday rotation has a small temperature coefficient and large wavelength stability, in order to improve the stability of device isolation against temperature and wavelength changes. High doped Bi ion series rare earth iron garnet single crystals and thin films have become the focus of research.
Bi3Fe5O12 (BiG) single crystal thin film brings hope for the development of integrated small magneto optical isolators. In 1988, T Kouda et al. obtained Bi3FesO12 (BiIG) single crystal thin films for the first time using reactive plasma sputtering deposition method RIBS (reaction lon bean sputtering). Subsequently, the United States, Japan, France, and others successfully obtained Bi3Fe5O12 and high Bi doped rare earth iron garnet magneto-optical films using various methods.
4. Ce doped rare earth iron garnet magneto-optical materials
Compared with commonly used materials such as YIG and GdBiIG, Ce doped rare earth iron garnet (Ce: YIG) has the characteristics of large Faraday rotation angle, low temperature coefficient, low absorption, and low cost. It is currently the most promising new type of Faraday rotation magneto-optical material.
Application of Rare Earth Magneto Optic Materials
Magneto optical crystal materials have a significant pure Faraday effect, low absorption coefficient at wavelengths, and high magnetization and permeability. Mainly used in the production of optical isolators, optical non reciprocal components, magneto optical memory and magneto optical modulators, fiber optic communication and integrated optical devices, computer storage, logic operation and transmission functions, magneto optical displays, magneto optical recording, new microwave devices, laser gyroscopes, etc. With the continuous discovery of magneto-optical crystal materials, the range of devices that can be applied and manufactured will also increase.
(1) Optical isolator
In optical systems such as fiber optic communication, there is light that returns to the laser source due to the reflection surfaces of various components in the optical path. This light makes the output light intensity of the laser source unstable, causing optical noise, and greatly limiting the transmission capacity and communication distance of signals in fiber optic communication, making the optical system unstable in operation. An optical isolator is a passive optical device that only allows unidirectional light to pass through, and its working principle is based on the non reciprocity of Faraday rotation. The light reflected through fiber optic echoes can be well isolated by optical isolators.
(2) Magneto optic current tester
The rapid development of modern industry has put forward higher requirements for the transmission and detection of power grids, and traditional high-voltage and high current measurement methods will face severe challenges. With the development of fiber optic technology and material science, magneto-optical current testers have gained widespread attention due to their excellent insulation and anti-interference capabilities, high measurement accuracy, easy miniaturization, and no potential explosion hazards.
(3) Microwave device
YIG has the characteristics of narrow ferromagnetic resonance line, dense structure, good temperature stability, and very small characteristic electromagnetic loss at high frequencies. These characteristics make it suitable for making various microwave devices such as high-frequency synthesizers, bandpass filters, oscillators, AD tuning drivers, etc. It has been widely used in the microwave frequency band below the X-ray band. In addition, magneto-optical crystals can also be made into magneto-optical devices such as ring-shaped devices and magneto-optical displays.
(4) Magneto optical memory
In information processing technology, magneto-optical media are used for recording and storing information. Magneto optical storage is the leader in optical storage, with the characteristics of large capacity and free swapping of optical storage, as well as the advantages of erasable rewriting of magnetic storage and average access speed similar to magnetic hard drives. The cost performance ratio will be the key to whether magneto optical disks can lead the way.
(5) TG single crystal
TGG is a crystal developed by Fujian Fujing Technology Co., Ltd. (CASTECH) in 2008. Its main advantages: TGG single crystal has a large magneto-optical constant, high thermal conductivity, low optical loss, and high laser damage threshold, and is widely used in multi-level amplification, ring, and seed injection lasers such as YAG and T-doped sapphire