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Magnetoresistance
Magnetoresistance is the tendency of a material (often ferromagnetic) to change the value of its electrical resistance in an externally-applied magnetic field. There are a variety of effects that can be called magnetoresistance. Some occur in bulk non-magnetic metals and semiconductors, such as geometrical magnetoresistance, Shubnikov–de Haas oscillations, or the common positive magnetoresistance in metals. Other effects occur in magnetic metals, such as negative magnetoresistance in ferromagnets or anisotropic magnetoresistance (AMR). Finally, in multicomponent or multilayer systems (e.g. magnetic tunnel junctions), giant magnetoresistance (GMR), tunnel magnetoresistance (TMR), colossal magnetoresistance (CMR), and extraordinary magnetoresistance (EMR) can be observed. The first magnetoresistive effect was discovered in 1856 by William Thomson, better known as Lord Kelvin, but he was unable to lower the electrical resistance of anything by more than 5%. Today, systems includi ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Giant Magnetoresistance
Giant magnetoresistance (GMR) is a quantum mechanical magnetoresistance effect observed in multilayers composed of alternating ferromagnetic and non-magnetic conductive layers. The 2007 Nobel Prize in Physics was awarded to Albert Fert and Peter Grünberg for the discovery of GMR. The effect is observed as a significant change in the electrical resistance depending on whether the magnetization of adjacent ferromagnetic layers are in a parallel or an antiparallel alignment. The overall resistance is relatively low for parallel alignment and relatively high for antiparallel alignment. The magnetization direction can be controlled, for example, by applying an external magnetic field. The effect is based on the dependence of electron scattering on spin orientation. The main application of GMR is in magnetic field sensors, which are used to read data in hard disk drives, biosensors, microelectromechanical systems (MEMS) and other devices. GMR multilayer structures are also used in m ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Giant Magnetoresistance
Giant magnetoresistance (GMR) is a quantum mechanical magnetoresistance effect observed in multilayers composed of alternating ferromagnetic and non-magnetic conductive layers. The 2007 Nobel Prize in Physics was awarded to Albert Fert and Peter Grünberg for the discovery of GMR. The effect is observed as a significant change in the electrical resistance depending on whether the magnetization of adjacent ferromagnetic layers are in a parallel or an antiparallel alignment. The overall resistance is relatively low for parallel alignment and relatively high for antiparallel alignment. The magnetization direction can be controlled, for example, by applying an external magnetic field. The effect is based on the dependence of electron scattering on spin orientation. The main application of GMR is in magnetic field sensors, which are used to read data in hard disk drives, biosensors, microelectromechanical systems (MEMS) and other devices. GMR multilayer structures are also used in m ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Colossal Magnetoresistance
Colossal magnetoresistance (CMR) is a property of some materials, mostly manganese-based perovskite oxides, that enables them to dramatically change their electrical resistance in the presence of a magnetic field. The magnetoresistance of conventional materials enables changes in resistance of up to 5%, but materials featuring CMR may demonstrate resistance changes by orders of magnitude. This technology may find uses in disk read-and-write heads, allowing for increases in hard disk drive data density. However, so far it has not led to practical applications because it requires low temperatures and bulky equipment. History Initially discovered in mixed-valence perovskite manganites in the 1950s by G. H. Jonker and J. H. van Santen, a first theoretical description in terms of the double-exchange mechanism was given early on. In this model, the spin orientation of adjacent Mn moments is associated with kinetic exchange of eg-electrons. Consequently, alignment o ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Tunnel Magnetoresistance
Tunnel magnetoresistance (TMR) is a magnetoresistive effect that occurs in a magnetic tunnel junction (MTJ), which is a component consisting of two ferromagnets separated by a thin insulator. If the insulating layer is thin enough (typically a few nanometres), electrons can tunnel from one ferromagnet into the other. Since this process is forbidden in classical physics, the tunnel magnetoresistance is a strictly quantum mechanical phenomenon. Magnetic tunnel junctions are manufactured in thin film technology. On an industrial scale the film deposition is done by magnetron sputter deposition; on a laboratory scale molecular beam epitaxy, pulsed laser deposition and electron beam physical vapor deposition are also utilized. The junctions are prepared by photolithography. Phenomenological description The direction of the two magnetizations of the ferromagnetic films can be switched individually by an external magnetic field. If the magnetizations are in a parallel orientation it ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Tunnel Magnetoresistance
Tunnel magnetoresistance (TMR) is a magnetoresistive effect that occurs in a magnetic tunnel junction (MTJ), which is a component consisting of two ferromagnets separated by a thin insulator. If the insulating layer is thin enough (typically a few nanometres), electrons can tunnel from one ferromagnet into the other. Since this process is forbidden in classical physics, the tunnel magnetoresistance is a strictly quantum mechanical phenomenon. Magnetic tunnel junctions are manufactured in thin film technology. On an industrial scale the film deposition is done by magnetron sputter deposition; on a laboratory scale molecular beam epitaxy, pulsed laser deposition and electron beam physical vapor deposition are also utilized. The junctions are prepared by photolithography. Phenomenological description The direction of the two magnetizations of the ferromagnetic films can be switched individually by an external magnetic field. If the magnetizations are in a parallel orientation it ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Extraordinary Magnetoresistance
Extraordinary magnetoresistance (EMR) is a geometrical magnetoresistance Magnetoresistance is the tendency of a material (often ferromagnetic) to change the value of its electrical resistance in an externally-applied magnetic field. There are a variety of effects that can be called magnetoresistance. Some occur in bulk ... effect discovered in 2000, where the change in electrical resistance upon the application of a large magnetic field can be greater than 1,000,000% at room temperature (orders of magnitude greater than other magnetoresistance effects such as GMR and CMR). The effect occurs in semiconductor-metal hybrid systems when a transverse magnetic field is applied. Without a magnetic field the system is in a low-resistance state with most of the current flow directed through the metallic region. Upon the application of a large magnetic field the system switches to a state of much higher electrical resistance, due to the Hall angle approaching 90°, with the current flow ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Extraordinary Magnetoresistance
Extraordinary magnetoresistance (EMR) is a geometrical magnetoresistance Magnetoresistance is the tendency of a material (often ferromagnetic) to change the value of its electrical resistance in an externally-applied magnetic field. There are a variety of effects that can be called magnetoresistance. Some occur in bulk ... effect discovered in 2000, where the change in electrical resistance upon the application of a large magnetic field can be greater than 1,000,000% at room temperature (orders of magnitude greater than other magnetoresistance effects such as GMR and CMR). The effect occurs in semiconductor-metal hybrid systems when a transverse magnetic field is applied. Without a magnetic field the system is in a low-resistance state with most of the current flow directed through the metallic region. Upon the application of a large magnetic field the system switches to a state of much higher electrical resistance, due to the Hall angle approaching 90°, with the current flow ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Barber Pole
A barber's pole is a type of sign used by barbers to signify the place or shop where they perform their craft. The trade sign is, by a tradition dating back to the Middle Ages, a staff or pole with a helix of colored stripes (often red and white in many countries, but usually red, white and blue in the United States). The pole may be stationary or may rotate, often with the aid of an electric motor. A "barber's pole" with a helical stripe is a familiar sight, and is used as a secondary metaphor to describe objects in many other contexts. For example, if the shaft or tower of a lighthouse has been painted with a helical stripe as a daymark, the lighthouse could be described as having been painted in "barber's pole" colors. Origin in barbering and surgery During medieval times, barbers performed surgery on customers, as well as tooth extractions. The original pole had a brass wash basin at the top (representing the vessel in which leeches were kept) and bottom (representi ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Albert Fert
Albert Fert (; born 7 March 1938) is a French physicist and one of the discoverers of giant magnetoresistance which brought about a breakthrough in gigabyte hard disks. Currently, he is an emeritus professor at Paris-Saclay University in Orsay, scientific director of a joint laboratory (''Unité mixte de recherche'') between the Centre national de la recherche scientifique (National Scientific Research Centre) and Thales Group, and adjunct professor at Michigan State University. He was awarded the 2007 Nobel Prize in Physics together with Peter Grünberg. Biography In 1962 Albert Fert graduated from the École Normale Supérieure in Paris, where he attended courses by the physicists Alfred Kastler and Jacques Friedel. (As an undergraduate he had strong interests in photography and cinema, and was a great admirer of the work of Ingmar Bergman).) After the École Normale Supérieure, Fert attended the University of Grenoble and in 1963 received his Ph.D. (''doctorat de troisiè ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Lorentz Force
In physics (specifically in electromagnetism) the Lorentz force (or electromagnetic force) is the combination of electric and magnetic force on a point charge due to electromagnetic fields. A particle of charge moving with a velocity in an electric field and a magnetic field experiences a force of \mathbf = q\,\mathbf + q\,\mathbf \times \mathbf (in SI unitsIn SI units, is measured in teslas (symbol: T). In Gaussian-cgs units, is measured in gauss (symbol: G). See e.g. )The -field is measured in amperes per metre (A/m) in SI units, and in oersteds (Oe) in cgs units. ). It says that the electromagnetic force on a charge is a combination of a force in the direction of the electric field proportional to the magnitude of the field and the quantity of charge, and a force at right angles to the magnetic field and the velocity of the charge, proportional to the magnitude of the field, the charge, and the velocity. Variations on this basic formula describe the magnetic force on ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
William Thomson, 1st Baron Kelvin
William Thomson, 1st Baron Kelvin, (26 June 182417 December 1907) was a British mathematician, mathematical physicist and engineer born in Belfast. Professor of Natural Philosophy at the University of Glasgow for 53 years, he did important work in the mathematical analysis of electricity and formulation of the first and second laws of thermodynamics, and did much to unify the emerging discipline of physics in its contemporary form. He received the Royal Society's Copley Medal in 1883, was its president 1890–1895, and in 1892 was the first British scientist to be elevated to the House of Lords. Absolute temperatures are stated in units of kelvin in his honour. While the existence of a coldest possible temperature ( absolute zero) was known prior to his work, Kelvin is known for determining its correct value as approximately −273.15 degrees Celsius or −459.67 degrees Fahrenheit. The Joule–Thomson effect is also named in his honour. He worked closely with mathematics ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Semimetal
A semimetal is a material with a very small overlap between the bottom of the conduction band and the top of the valence band. According to electronic band theory, solids can be classified as insulators, semiconductors, semimetals, or metals. In insulators and semiconductors the filled valence band is separated from an empty conduction band by a band gap. For insulators, the magnitude of the band gap is larger (e.g., > 4 eV) than that of a semiconductor (e.g., < 4 eV). Because of the slight overlap between the conduction and valence bands, semimetals have no band gap and a negligible at the Fermi level. A metal, by contrast, has an appreciable density of states at the Fermi level because the conduction band is partially filled. ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
