Magnetic semiconductor

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Unsolved problem in physics:

Can we build materials that show properties of both ferromagnets and semiconductors at room temperature?

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(more unsolved problems in physics)

Magnetic semiconductors are semiconductor materials that exhibit both ferromagnetism (or a similar response) and useful semiconductor properties. If implemented in devices, these materials could provide a new type of control of conduction. Whereas traditional electronics are based on control of charge carriers (n- or p-type), practical magnetic semiconductors would also allow control of quantum spin state (up or down). This would theoretically provide near-total spin polarization (as opposed to iron and other metals, which provide only ~50% polarization), which is an important property for spintronics applications, e.g. spin transistors.

While many traditional magnetic materials, such as magnetite, are also semiconductors (magnetite is a semimetal semiconductor with bandgap 0.14 eV), materials scientists generally predict that magnetic semiconductors will only find widespread use if they are similar to well-developed semiconductor materials. To that end, dilute magnetic semiconductors (DMS) have recently been a major focus of magnetic semiconductor research. These are based on traditional semiconductors, but are doped with transition metals instead of, or in addition to, electronically active elements. They are of interest because of their unique spintronics properties with possible technological applications. [1] [2] Doped wide band-gap metal oxides such as zinc oxide (ZnO) and titanium oxide (TiO2) are among the best candidates for industrial DMS due to their multifunctionality in opticomagnetic applications. In particular, ZnO-based DMS with properties such as transparency in visual region and piezoelectricity have generated huge interest among the scientific community as a strong candidate for the fabrication of spin transistors and spin-polarized light-emitting diodes, [3] while copper doped TiO2 in the anatase phase of this material has further been predicted to exhibit favorable dilute magnetism. [4]

Hideo Ohno and his group at the Tohoku University were the first to measure ferromagnetism in transition metal doped compound semiconductors such as indium arsenide [5] and gallium arsenide [6] doped with manganese (the latter is commonly referred to as GaMnAs). These materials exhibited reasonably high Curie temperatures (yet below room temperature) that scales with the concentration of p-type charge carriers. Ever since, ferromagnetic signals have been measured from various semiconductor hosts doped with different transition atoms.

Theory

The pioneering work of Dietl et al. showed that a modified Zener model for magnetism [7] well describes the carrier dependence, as well as anisotropic properties of GaMnAs. The same theory also predicted that room-temperature ferromagnetism should exist in heavily p-type doped ZnO and GaN doped by Co and Mn, respectively. These predictions were followed of a flurry of theoretical and experimental studies of various oxide and nitride semiconductors, which apparently seemed to confirm room temperature ferromagnetism in nearly any semiconductor or insulator material heavily doped by transition metal impurities. However, early Density functional theory (DFT) studies were clouded by band gap errors and overly delocalized defect levels, and more advanced DFT studies refute most of the previous predictions of ferromagnetism. [8] Likewise, it has been shown that for most of the oxide based materials studies for magnetic semiconductors do not exhibit an intrinsic carrier-mediated ferromagnetism as postulated by Dietl et al. [9] To date, GaMnAs remains the only semiconductor material with robust coexistence of ferromagnetism persisting up to rather high Curie temperatures around 100–200 K.

Materials

The manufacturability of the materials depend on the thermal equilibrium solubility of the dopant in the base material. E.g., solubility of many dopants in zinc oxide is high enough to prepare the materials in bulk, while some other materials have so low solubility of dopants that to prepare them with high enough dopant concentration thermal nonequilibrium preparation mechanisms have to be employed, e.g. growth of thin films.

Permanent magnetization has been observed in a wide range of semiconductor based materials. Some of them exhibit a clear correlation between carrier density and magnetization, including the work of T. Story and co-workers where they demonstrated that the ferromagnetic Curie temperature of Mn2+-doped Pb1−xSnxTe can be controlled by the carrier concentration. [10] The theory proposed by Dietl required charge carriers in the case of holes to mediate the magnetic coupling of manganese dopants in the prototypical magnetic semiconductor, Mn2+-doped GaAs. If there is an insufficient hole concentration in the magnetic semiconductor, then the Curie temperature would be very low or would exhibit only paramagnetism. However, if the hole concentration is high (>~1020 cm−3), then the Curie temperature would be higher, between 100 and 200 K. [7] However, many of the semiconductor materials studied exhibit a permanent magnetization extrinsic to the semiconductor host material. [9] A lot of the elusive extrinsic ferromagnetism (or phantom ferromagnetism) is observed in thin films or nanostructured materials. [11]

Several examples of proposed ferromagnetic semiconductor materials are listed below. Notice that many of the observations and/or predictions below remain heavily debated.

Related Research Articles

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.

<span class="mw-page-title-main">Zinc oxide</span> White powder insoluble in water

Zinc oxide is an inorganic compound with the formula ZnO. It is a white powder that is insoluble in water. ZnO is used as an additive in numerous materials and products including cosmetics, food supplements, rubbers, plastics, ceramics, glass, cement, lubricants, paints, sunscreens, ointments, adhesives, sealants, pigments, foods, batteries, ferrites, fire retardants, semi conductors, and first-aid tapes. Although it occurs naturally as the mineral zincite, most zinc oxide is produced synthetically.

<span class="mw-page-title-main">Doping (semiconductor)</span> Intentional introduction of impurities into an intrinsic semiconductor

In semiconductor production, doping is the intentional introduction of impurities into an intrinsic (undoped) semiconductor for the purpose of modulating its electrical, optical and structural properties. The doped material is referred to as an extrinsic semiconductor.

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.

Multiferroics are defined as materials that exhibit more than one of the primary ferroic properties in the same phase:

<span class="mw-page-title-main">Heusler compound</span>

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.)

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.

<span class="mw-page-title-main">Double-exchange mechanism</span>

The double-exchange mechanism is a type of a magnetic exchange that may arise between ions in different oxidation states. First proposed by Clarence Zener, this theory predicts the relative ease with which an electron may be exchanged between two species and has important implications for whether materials are ferromagnetic, antiferromagnetic, or exhibit spiral magnetism. For example, consider the 180 degree interaction of Mn-O-Mn in which the Mn "eg" orbitals are directly interacting with the O "2p" orbitals, and one of the Mn ions has more electrons than the other. In the ground state, electrons on each Mn ion are aligned according to the Hund's rule:

<span class="mw-page-title-main">Indium(III) oxide</span> Chemical compound

Indium(III) oxide (In2O3) is a chemical compound, an amphoteric oxide of indium.

<span class="mw-page-title-main">Half-metal</span>

A half-metal is any substance that acts as a conductor to electrons of one spin orientation, but as an insulator or semiconductor to those of the opposite orientation. Although all half-metals are ferromagnetic, most ferromagnets are not half-metals. Many of the known examples of half-metals are oxides, sulfides, or Heusler alloys. Types of half-metallic compounds theoretically predicted so far include some Heusler alloys, such as Co2FeSi, NiMnSb, and PtMnSb; some Si-containing half–Heusler alloys with Curie temperatures over 600 K, such as NiCrSi and PdCrSi; some transition-metal oxides, including rutile structured CrO2; some perovskites, such as LaMnO3 and SeMnO3; and a few more simply structured zincblende (ZB) compounds, including CrAs and superlattices. NiMnSb and CrO2 have been experimentally determined to be half-metals at very low temperatures.

<span class="mw-page-title-main">Lanthanum strontium manganite</span>

Lanthanum strontium manganite (LSM or LSMO) is an oxide ceramic material with the general formula La1−xSrxMnO3, where x describes the doping level.

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.

<span class="mw-page-title-main">Lanthanum aluminate-strontium titanate interface</span>

The interface between lanthanum aluminate (LaAlO3) and strontium titanate (SrTiO3) is a notable materials interface because it exhibits properties not found in its constituent materials. Individually, LaAlO3 and SrTiO3 are non-magnetic insulators, yet LaAlO3/SrTiO3 interfaces can exhibit electrical metallic conductivity, superconductivity, ferromagnetism, large negative in-plane magnetoresistance, and giant persistent photoconductivity. The study of how these properties emerge at the LaAlO3/SrTiO3 interface is a growing area of research in condensed matter physics.

Lanthanum manganite is an inorganic compound with the formula LaMnO3, often abbreviated as LMO. Lanthanum manganite is formed in the perovskite structure, consisting of oxygen octahedra with a central Mn atom. The cubic perovskite structure is distorted into an orthorhombic structure by a strong Jahn–Teller distortion of the oxygen octahedra.

Band-gap engineering is the process of controlling or altering the band gap of a material. This is typically done to semiconductors by controlling the composition of alloys, constructing layered materials with alternating compositions, or by inducing strain either epitaxially or topologically. A band gap is the range in a solid where no electron state can exist. The band gap of insulators is much larger than in semiconductors. Conductors or metals have a much smaller or nonexistent band gap than semiconductors since the valence and conduction bands overlap. Controlling the band gap allows for the creation of desirable electrical properties.

Professor Lan Wang is a Chinese-Australian material scientist known for expertise in materials synthesis and advanced materials characterisation.

Mohindar Singh Seehra is an Indian-American Physicist, academic and researcher. He is Eberly Distinguished Professor Emeritus at West Virginia University (WVU).

<span class="mw-page-title-main">Jeremy Levy</span> American physicist

Jeremy Levy is an American physicist who is a Distinguished Professor of Physics at the University of Pittsburgh.

Jacek K. Furdyna is a Polish American physicist and academic. He is a Professor Emeritus at the University of Notre Dame.

References

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  2. ↑ Ohno, H. (1998). "Making Nonmagnetic Semiconductors Ferromagnetic". Science. 281 (5379): 951–5. Bibcode:1998Sci...281..951O. doi:10.1126/science.281.5379.951. PMID   9703503.
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  9. 1 2 J. M. D. Coey, P. Stamenov, R. D. Gunning, M. Venkatesan, and K. Paul (2010). "Ferromagnetism in defect-ridden oxides and related materials". New Journal of Physics . 12 (5): 053025. arXiv: 1003.5558 . Bibcode:2010NJPh...12e3025C. doi:10.1088/1367-2630/12/5/053025. S2CID   55748696.{{cite journal}}: CS1 maint: multiple names: authors list (link)
  10. ↑ Story, T.; Gała̧zka, R.; Frankel, R.; Wolff, P. (1986). "Carrier-concentration–induced ferromagnetism in PbSnMnTe". Physical Review Letters . 56 (7): 777–779. Bibcode:1986PhRvL..56..777S. doi:10.1103/PhysRevLett.56.777. PMID   10033282.
  11. ↑ L. M. C. Pereira (2017). "Experimentally evaluating the origin of dilute magnetism in nanomaterials". Journal of Physics D: Applied Physics . 50 (39): 393002. Bibcode:2017JPhD...50M3002P. doi:10.1088/1361-6463/aa801f. S2CID   126213268.
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  15. ↑ Raebiger, Hannes; Lany, Stephan; Zunger, Alex (2008-07-07). "Control of Ferromagnetism via Electron Doping in In 2 O 3 : Cr". Physical Review Letters. 101 (2): 027203. Bibcode:2008PhRvL.101b7203R. doi:10.1103/PhysRevLett.101.027203. ISSN   0031-9007. PMID   18764222.
  16. ↑ Kittilstved, Kevin; Schwartz, Dana; Tuan, Allan; Heald, Steve; Chambers, Scott; Gamelin, Daniel (2006). "Direct Kinetic Correlation of Carriers and Ferromagnetism in Co2+: ZnO". Physical Review Letters. 97 (3): 037203. Bibcode:2006PhRvL..97c7203K. doi:10.1103/PhysRevLett.97.037203. PMID   16907540.
  17. ↑ Lany, Stephan; Raebiger, Hannes; Zunger, Alex (2008-06-03). "Magnetic interactions of Cr − Cr and Co − Co impurity pairs in ZnO within a band-gap corrected density functional approach". Physical Review B. 77 (24): 241201. Bibcode:2008PhRvB..77x1201L. doi:10.1103/PhysRevB.77.241201. ISSN   1098-0121.
  18. ↑ Martínez-Boubeta, C.; Beltrán, J. I.; Balcells, Ll.; Konstantinović, Z.; Valencia, S.; Schmitz, D.; Arbiol, J.; Estrade, S.; Cornil, J. (2010-07-08). "Ferromagnetism in transparent thin films of MgO" (PDF). Physical Review B. 82 (2): 024405. Bibcode:2010PhRvB..82b4405M. doi:10.1103/PhysRevB.82.024405. hdl: 2445/33086 .
  19. ↑ Jambois, O.; Carreras, P.; Antony, A.; Bertomeu, J.; Martínez-Boubeta, C. (2011-12-01). "Resistance switching in transparent magnetic MgO films". Solid State Communications. 151 (24): 1856–1859. Bibcode:2011SSCom.151.1856J. doi:10.1016/j.ssc.2011.10.009. hdl: 2445/50485 .
  20. ↑ "New room-temperature magnetic semiconductor material holds promise for 'spintronics' data-storage devices". KurzweilAI. Retrieved 2013-09-17.
  21. ↑ Lee, Y. F.; Wu, F.; Kumar, R.; Hunte, F.; Schwartz, J.; Narayan, J. (2013). "Epitaxial integration of dilute magnetic semiconductor Sr3SnO with Si (001)". Applied Physics Letters. 103 (11): 112101. Bibcode:2013ApPhL.103k2101L. doi:10.1063/1.4820770.
  22. ↑ Chambers, Scott A. (2010). "Epitaxial Growth and Properties of Doped Transition Metal and Complex Oxide Films". Advanced Materials. 22 (2): 219–248. Bibcode:2010AdM....22..219C. doi: 10.1002/adma.200901867 . PMID   20217685. S2CID   5415994.
  23. ↑ Frandsen, Benjamin A.; Gong, Zizhou; Terban, Maxwell W.; Banerjee, Soham; Chen, Bijuan; Jin, Changqing; Feygenson, Mikhail; Uemura, Yasutomo J.; Billinge, Simon J. L. (2016-09-06). "Local atomic and magnetic structure of dilute magnetic semiconductor ( Ba , K ) ( Zn , Mn ) 2 As 2". Physical Review B. 94 (9): 094102. arXiv: 1608.02684 . Bibcode:2016PhRvB..94i4102F. doi: 10.1103/PhysRevB.94.094102 . ISSN   2469-9950.
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