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Superconductivity is a set of physical properties observed in certain materials where electrical resistance vanishes and magnetic fields are expelled from the material. Any material exhibiting these properties is a superconductor. Unlike an ordinary metallic conductor, whose resistance decreases gradually as its temperature is lowered, even down to near absolute zero, a superconductor has a characteristic critical temperature below which the resistance drops abruptly to zero. An electric current through a loop of superconducting wire can persist indefinitely with no power source.
Magnetoresistance is the tendency of a material 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, giant magnetoresistance (GMR), tunnel magnetoresistance (TMR), colossal magnetoresistance (CMR), and extraordinary magnetoresistance (EMR) can be observed.
Spintronics, also known as spin electronics, is the study of the intrinsic spin of the electron and its associated magnetic moment, in addition to its fundamental electronic charge, in solid-state devices. The field of spintronics concerns spin-charge coupling in metallic systems; the analogous effects in insulators fall into the field of multiferroics.
An electromagnet is a type of magnet in which the magnetic field is produced by an electric current. Electromagnets usually consist of wire wound into a coil. A current through the wire creates a magnetic field which is concentrated in the hole in the center of the coil. The magnetic field disappears when the current is turned off. The wire turns are often wound around a magnetic core made from a ferromagnetic or ferrimagnetic material such as iron; the magnetic core concentrates the magnetic flux and makes a more powerful magnet.
Drum memory was a magnetic data storage device invented by Gustav Tauschek in 1932 in Austria. Drums were widely used in the 1950s and into the 1960s as computer memory.
In materials that exhibit antiferromagnetism, the magnetic moments of atoms or molecules, usually related to the spins of electrons, align in a regular pattern with neighboring spins pointing in opposite directions. This is, like ferromagnetism and ferrimagnetism, a manifestation of ordered magnetism. The phenomenon of antiferromagnetism was first introduced by Lev Landau in 1933.
BESK was Sweden's first electronic computer, using vacuum tubes instead of relays. It was developed by Matematikmaskinnämnden and for a short time it was the fastest computer in the world. The computer was completed in 1953 and in use until 1966. The technology behind BESK was later continued with the transistorized FACIT EDB and FACIT EDB-3 machines, both software compatible with BESK. Non-compatible machines highly inspired by BESK were SMIL made for the University of Lund, SAABs räkneautomat SARA, "SAAB's calculating machine", and DASK made in Denmark.
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, 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 storage or magnetic recording is the storage of data on a magnetized medium. Magnetic storage uses different patterns of magnetisation in a magnetizable material to store data and is a form of non-volatile memory. The information is accessed using one or more read/write heads.
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.
Magnetostatics is the study of magnetic fields in systems where the currents are steady. It is the magnetic analogue of electrostatics, where the charges are stationary. The magnetization need not be static; the equations of magnetostatics can be used to predict fast magnetic switching events that occur on time scales of nanoseconds or less. Magnetostatics is even a good approximation when the currents are not static – as long as the currents do not alternate rapidly. Magnetostatics is widely used in applications of micromagnetics such as models of magnetic storage devices as in computer memory.
A magnetic core is a piece of magnetic material with a high magnetic permeability used to confine and guide magnetic fields in electrical, electromechanical and magnetic devices such as electromagnets, transformers, electric motors, generators, inductors, magnetic recording heads, and magnetic assemblies. It is made of ferromagnetic metal such as iron, or ferrimagnetic compounds such as ferrites. The high permeability, relative to the surrounding air, causes the magnetic field lines to be concentrated in the core material. The magnetic field is often created by a current-carrying coil of wire around the core.
Exchange bias or exchange anisotropy occurs in bilayers of magnetic materials where the hard magnetization behavior of an antiferromagnetic thin film causes a shift in the soft magnetization curve of a ferromagnetic film. The exchange bias phenomenon is of tremendous utility in magnetic recording, where it is used to pin the state of the readback heads of hard disk drives at exactly their point of maximum sensitivity; hence the term "bias."
Heusler compounds are magnetic intermetallics with face-centered cubic crystal structure and a composition of XYZ (half-Heuslers) or X2YZ (full-Heuslers), where X and Y are transition metals and Z is in the p-block. The term derives from the name of German mining engineer and chemist Friedrich Heusler, who studied such a compound (Cu2MnAl) in 1903. Many of these compounds exhibit properties relevant to spintronics, such as magnetoresistance, variations of the Hall effect, ferro-, antiferro-, and ferrimagnetism, half- and semimetallicity, semiconductivity with spin filter ability, superconductivity, topological band structure and are actively studied as Thermoelectric materials. Their magnetism results from a double-exchange mechanism between neighboring magnetic ions. Manganese, which sits at the body centers of the cubic structure, was the magnetic ion in the first Heusler compound discovered. (See the Bethe–Slater curve for details of why this happens.)
Stuart Stephen Papworth Parkin is an experimental physicist, director at the Max Planck Institute of Microstructure Physics in Halle and an Alexander von Humboldt Professor at the Institute of Physics of the Martin-Luther-University Halle-Wittenberg.
Kathryn Ann Moler is an American physicist, and current dean of research at Stanford University. She received her BSc (1988) and Ph.D. (1995) from Stanford University. After working as a visiting scientist at IBM T.J. Watson Research Center in 1995, she held a postdoctoral position at Princeton University from 1995 to 1998. She joined the faculty of Stanford University in 1998, and became an Associate in CIFAR's Superconductivity Program in 2000. She became an associate professor at Stanford in 2002 and is currently a professor of applied physics and of Physics at Stanford. She currently works in the Geballe Laboratory for Advanced Materials (GLAM), and is the director of the Center for Probing the Nanoscale (CPN), a National Science Foundation-funded center where Stanford and IBM scientists continue to improve scanning probe methods for measuring, imaging, and controlling nanoscale phenomena. She lists her scientific interests and main areas of research and experimentation as:
Solid-state storage (SSS) is a type of non-volatile computer storage that stores and retrieves digital information using only electronic circuits, without any involvement of moving mechanical parts. This differs fundamentally from the traditional electromechanical storage, which records data using rotating or linearly moving media coated with magnetic material.
Carousel memory is a type of secondary storage for computers, which was created by Swedish computer engineers Erik Stemme and Gunnar Stenudd. It was first shown at an exhibition in Paris in 1958.
Electromagnetically induced acoustic noise (and vibration), electromagnetically excited acoustic noise, or more commonly known as coil whine, is audible sound directly produced by materials vibrating under the excitation of electromagnetic forces. Some examples of this noise include the mains hum, hum of transformers, the whine of some rotating electric machines, or the buzz of fluorescent lamps. The hissing of high voltage transmission lines is due to corona discharge, not magnetism.
Twistronics is the study of how the angle between layers of two-dimensional materials can change their electrical properties. Materials such as bilayer graphene have been shown to have vastly different electronic behavior, ranging from non-conductive to superconductive, that depends sensitively on the angle between the layers. The term was first introduced by the research group of Efthimios Kaxiras at Harvard University in their theoretical treatment of graphene superlattices.
References
- 1 2 Jan Karlqvist (1999), Olle Karlqvist, datorpionär och upptäckare av "Karlqvist field"(gap) [Olle Karlqvist, computer pioneer and discoverer of the "Karlqvist field"(gap)] (in Swedish), retrieved 2010-12-23 (HTML 3 kB)
- ↑ Jan Karlqvist (1999), The Karlqvist field (in Swedish), retrieved 2010-12-23 (HTML 1 kB)
- ↑ Olle Karlqvist (1954), Calculation of the magnetic field in ferromagnetic layer of a magnetic drum (PDF) (in Swedish), AB Henrik Lindstahls Bokhandel i distribution (published 2013-07-15) (PDF 741 kB)
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