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Condensed matter physics is the field of physics that deals with the macroscopic and microscopic physical properties of matter, especially the solid and liquid phases which arise from electromagnetic forces between atoms and electrons. More generally, the subject deals with condensed phases of matter: systems of many constituents with strong interactions among them. More exotic condensed phases include the superconducting phase exhibited by certain materials at extremely low cryogenic temperatures, the ferromagnetic and antiferromagnetic phases of spins on crystal lattices of atoms, the Bose–Einstein condensates found in ultracold atomic systems, and liquid crystals. Condensed matter physicists seek to understand the behavior of these phases by experiments to measure various material properties, and by applying the physical laws of quantum mechanics, electromagnetism, statistical mechanics, and other physics theories to develop mathematical models and predict the properties of extremely large groups of atoms.
Ferromagnetism is a property of certain materials that results in a significant, observable magnetic permeability, and in many cases, a significant magnetic coercivity, allowing the material to form a permanent magnet. Ferromagnetic materials are familiar metals that are noticeably attracted to a magnet, a consequence of their substantial magnetic permeability. Magnetic permeability describes the induced magnetization of a material due to the presence of an external magnetic field. This temporarily induced magnetization, for example, inside a steel plate, accounts for its attraction to the permanent magnet. Whether or not that steel plate acquires a permanent magnetization itself depends not only on the strength of the applied field but on the so-called coercivity of the ferromagnetic material, which can vary greatly.
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.
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.
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.
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.
A magnon is a quasiparticle, a collective excitation of the spin structure of an electron in a crystal lattice. In the equivalent wave picture of quantum mechanics, a magnon can be viewed as a quantized spin wave. Magnons carry a fixed amount of energy and lattice momentum, and are spin-1, indicating they obey boson behavior.
Albert Fert 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 between the Centre national de la recherche scientifique and Thales Group, and adjunct professor at Michigan State University. He was awarded the 2007 Nobel Prize in Physics together with Peter Grünberg.
A two-dimensional electron gas (2DEG) is a scientific model in solid-state physics. It is an electron gas that is free to move in two dimensions, but tightly confined in the third. This tight confinement leads to quantized energy levels for motion in the third direction, which can then be ignored for most problems. Thus the electrons appear to be a 2D sheet embedded in a 3D world. The analogous construct of holes is called a two-dimensional hole gas (2DHG), and such systems have many useful and interesting properties.
Spin pumping is the dynamical generation of pure spin current by the coherent precession of magnetic moments, which can efficiently inject spin from a magnetic material into an adjacent non-magnetic material. The non-magnetic material usually hosts the spin Hall effect that can convert the injected spin current into a charge voltage easy to detect. A spin pumping experiment typically requires electromagnetic irradiation to induce magnetic resonance, which converts energy and angular momenta from electromagnetic waves to magnetic dynamics and then to electrons, enabling the electronic detection of electromagnetic waves. The device operation of spin pumping can be regarded as the spintronic analog of a battery.
Gallium manganese arsenide, chemical formula (Ga,Mn)As is a magnetic semiconductor. It is based on the world's second most commonly used semiconductor, gallium arsenide,, and readily compatible with existing semiconductor technologies. Differently from other dilute magnetic semiconductors, such as the majority of those based on II-VI semiconductors, it is not paramagnetic but ferromagnetic, and hence exhibits hysteretic magnetization behavior. This memory effect is of importance for the creation of persistent devices. In (Ga,Mn)As, the manganese atoms provide a magnetic moment, and each also acts as an acceptor, making it a p-type material. The presence of carriers allows the material to be used for spin-polarized currents. In contrast, many other ferromagnetic magnetic semiconductors are strongly insulating and so do not possess free carriers. (Ga,Mn)As is therefore a candidate as a spintronic material.
Molecule-based magnets (MBMs) or molecular magnets are a class of materials capable of displaying ferromagnetism and other more complex magnetic phenomena. This class expands the materials properties typically associated with magnets to include low density, transparency, electrical insulation, and low-temperature fabrication, as well as combine magnetic ordering with other properties such as photoresponsiveness. Essentially all of the common magnetic phenomena associated with conventional transition-metal magnets and rare-earth magnets can be found in molecule-based magnets. Prior to 2011, MBMs were seen to exhibit "magnetic ordering with Curie temperature (Tc) exceeding room temperature".
Spinmechatronics is neologism referring to an emerging field of research concerned with the exploitation of spin-dependent phenomena and established spintronic methodologies and technologies in conjunction with electro-mechanical, magno-mechanical, acousto-mechanical and opto-mechanical systems. Most especially, spinmechatronics concerns the integration of micro- and nano- mechatronic systems with spin physics and spintronics.
Magnonics is an emerging field of modern magnetism, which can be considered a sub-field of modern solid state physics. Magnonics combines the study of waves and magnetism. Its main aim is to investigate the behaviour of spin waves in nano-structure elements. In essence, spin waves are a propagating re-ordering of the magnetisation in a material and arise from the precession of magnetic moments. Magnetic moments arise from the orbital and spin moments of the electron, most often it is this spin moment that contributes to the net magnetic moment.
Spin Hall magnetoresistance (SMR) is a transport phenomenon that is found in some electrical conductors that have at least one surface in direct contact with another magnetic material due to changes in the spin current that are present in metals and semiconductors with a large spin Hall angle. It is most easily detected when the magnetic material is an insulator which eliminates other magnetically sensitive transport effects arising from conduction in the magnetic material.
Spinterface is a term coined to indicate an interface between a ferromagnet and an organic semiconductor. This is a widely investigated topic in molecular spintronics, since the role of interfaces plays a huge part in the functioning of a device. In particular, spinterfaces are widely studied in the scientific community because of their hybrid organic/inorganic composition. In fact, the hybridization between the metal and the organic material can be controlled by acting on the molecules, which are more responsive to electrical and optical stimuli than metals. This gives rise to the possibility of efficiently tuning the magnetic properties of the interface at the atomic scale.
Professor Lan Wang is a Chinese-Australian material scientist known for expertise in materials synthesis and advanced materials characterisation.
Joseph P. Heremans is a condensed matter experimental physicist at The Ohio State University where he holds titles as Ohio Eminent Scholar and Professor in the Department of Mechanical and Aerospace Engineering, with courtesy appointments in the Department of Physics and Department of Materials Science and Engineering. He is a member of the National Academy of Engineering and fellow of the American Physical Society and the American Association for the Advancement of Science. His research focuses on magneto-transport, thermal, and thermoelectric properties of electrons, phonons, and spin in narrow-gap semiconductors, semimetals, and nanostructures. Prior to OSU, Heremans worked as a research scientist and research manager at GM Research Lab from 1984-1998 and the Delphi Research Labs (1999-2005), where he developed tunable IR diode lasers and magnetic sensors.
Jean-Philippe Ansermet is a Swiss physicist and engineer and a professor at École Polytechnique Fédérale de Lausanne. His research focuses on the fabrication and properties of nanostructured materials as well as spintronics.
References
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- ↑ C Sandweg; et al. (2011). "Spin Pumping by Parametrically Excited Exchange Magnons". Physical Review Letters. 106 (21): 216601. arXiv: 1103.2229 . Bibcode:2011PhRvL.106u6601S. doi:10.1103/PhysRevLett.106.216601. PMID 21699324. S2CID 14519388.
- ↑ S Takahashi and S Maekawa (2008). "Spin current, spin accumulation and spin Hall effect*". Science and Technology of Advanced Materials . 9 (1): 014105. Bibcode:2008STAdM...9a4105T. doi:10.1088/1468-6996/9/1/014105. PMC 5099800 . PMID 27877931.
- ↑ J-C Le Breton; et al. (2011). "Thermal spin current from a ferromagnet to silicon by Seebeck spin tunnelling". Nature. 475 (7354): 82–85. Bibcode:2011Natur.475...82L. doi:10.1038/nature10224. PMID 21716285. S2CID 4422579.
- ↑ K. Uchida; et al. (2011). "Long-range spin Seebeck effect and acoustic spin pumping". Nature Materials. 10 (10): 737–741. arXiv: 1103.6120 . Bibcode:2011NatMa..10..737U. doi:10.1038/nmat3099. PMID 21857673. S2CID 118009611.
- ↑ G E Bauer and Y Tserkovnyak (2011). "Spin-magnon transmutation". Physics. 4: 40. Bibcode:2011PhyOJ...4...40B. doi: 10.1103/Physics.4.40 .
- ↑ Y Kajiwara; et al. (2010). "Transmission of electrical signals by spin-wave interconversion in a magnetic insulator". Nature. 464 (7286): 262–266. Bibcode:2010Natur.464..262K. doi:10.1038/nature08876. PMID 20220845. S2CID 4426579.
- ↑ S Sanvito; et al. (2011). "Organic spintronics: Filtering spins with molecules". Nature Materials. 10 (7): 484–485. Bibcode:2011NatMa..10..484S. doi:10.1038/nmat3061. PMID 21697848.