Editing Spintronics (section)

==Semiconductor-based spintronic devices==

Doped semiconductor materials display dilute ferromagnetism. In recent years, dilute magnetic oxides (DMOs) including [[ZnO-based diluted magnetic semiconductors|ZnO based DMOs]] and [[Anatase|TiO<sub>2</sub>]]-based DMOs have been the subject of numerous experimental and computational investigations.<ref>{{cite journal| last1=Assadi| first1=M.H.N| last2=Hanaor| first2=D.A.H| title= Theoretical study on copper's energetics and magnetism in TiO<sub>2</sub> polymorphs| journal= Journal of Applied Physics| date=2013| volume=113| issue=23| pages= 233913–233913–5| doi=10.1063/1.4811539|arxiv = 1304.1854 |bibcode = 2013JAP...113w3913A | s2cid=94599250}}</ref><ref>{{cite journal| last1=Ogale| first1=S.B| title= Dilute doping, defects, and ferromagnetism in metal oxide systems| journal= Advanced Materials| date=2010| volume=22| issue=29| pages= 3125–3155| doi=10.1002/adma.200903891| pmid=20535732| bibcode=2010AdM....22.3125O| s2cid=25307693}}</ref> Non-oxide ferromagnetic semiconductor sources (like manganese-doped gallium arsenide {{chem2|[[(Ga,Mn)As]]}}),<ref>{{Cite journal | last1 = Jonker | first1 = B. | last2 = Park | first2 = Y. | last3 = Bennett | first3 = B. | last4 = Cheong | first4 = H. | last5 = Kioseoglou | first5 = G. | last6 = Petrou | first6 = A. | doi = 10.1103/PhysRevB.62.8180 | title = Robust electrical spin injection into a semiconductor heterostructure | journal = Physical Review B | volume = 62 | issue = 12 | pages = 8180 | year = 2000 |bibcode = 2000PhRvB..62.8180J }}</ref> increase the interface resistance with a tunnel barrier,<ref>{{Cite journal | last1 = Hanbicki | first1 = A. T. | last2 = Jonker | first2 = B. T. | last3 = Itskos | first3 = G. | last4 = Kioseoglou | first4 = G. | last5 = Petrou | first5 = A. | title = Efficient electrical spin injection from a magnetic metal/tunnel barrier contact into a semiconductor | doi = 10.1063/1.1449530 | journal = Applied Physics Letters | volume = 80 | issue = 7 | pages = 1240 | year = 2002 |arxiv = cond-mat/0110059 |bibcode = 2002ApPhL..80.1240H | s2cid = 119098659 }}</ref> or using hot-electron injection.<ref>{{Cite journal | last1 = Jiang | first1 = X. | last2 = Wang | first2 = R. | last3 = Van Dijken | first3 = S. | last4 = Shelby | first4 = R. | last5 = MacFarlane | first5 = R. | last6 = Solomon | first6 = G. | last7 = Harris | first7 = J. | last8 = Parkin | first8 = S. | doi = 10.1103/PhysRevLett.90.256603 | title = Optical Detection of Hot-Electron Spin Injection into GaAs from a Magnetic Tunnel Transistor Source | journal = Physical Review Letters | volume = 90 | issue = 25 | year = 2003 | pmid =  12857153|bibcode = 2003PhRvL..90y6603J | page=256603}}</ref>

Spin detection in semiconductors has been addressed with multiple techniques:
* Faraday/Kerr rotation of transmitted/reflected photons<ref>{{Cite journal | last1 = Kikkawa | first1 = J. | last2 = Awschalom | first2 = D. | doi = 10.1103/PhysRevLett.80.4313 | title = Resonant Spin Amplification in n-Type GaAs | journal = Physical Review Letters | volume = 80 | issue = 19 | pages = 4313 | year = 1998 |bibcode = 1998PhRvL..80.4313K }}</ref>
* Circular polarization analysis of electroluminescence<ref>Jonker, Berend T. [http://www.patentstorm.us/patents/5874749.html Polarized optical emission due to decay or recombination of spin-polarized injected carriers – US Patent 5874749] {{webarchive |url=https://web.archive.org/web/20091212102246/http://www.patentstorm.us/patents/5874749.html |date=12 December 2009 }}. Issued on 23 February 1999.</ref>
* Nonlocal spin valve (adapted from Johnson and Silsbee's work with metals)<ref>{{Cite journal | last1 = Lou | first1 = X. | last2 = Adelmann | first2 = C. | last3 = Crooker | first3 = S. A. | last4 = Garlid | first4 = E. S. | last5 = Zhang | first5 = J. | last6 = Reddy | first6 = K. S. M. | last7 = Flexner | first7 = S. D. | last8 = Palmstrøm | first8 = C. J. | last9 = Crowell | first9 = P. A. | doi = 10.1038/nphys543 | title = Electrical detection of spin transport in lateral ferromagnet–semiconductor devices | journal = Nature Physics | volume = 3 | issue = 3 | pages = 197 | year = 2007 |bibcode = 2007NatPh...3..197L | arxiv = cond-mat/0701021 | s2cid = 51390849 }}</ref>
* Ballistic spin filtering<ref>{{Cite journal | last1 = Appelbaum | first1 = I. | last2 = Huang | first2 = B. | last3 = Monsma | first3 = D. J. | doi = 10.1038/nature05803 | title = Electronic measurement and control of spin transport in silicon | journal = Nature | volume = 447 | issue = 7142 | pages = 295–298 | year = 2007 | pmid =  17507978|arxiv = cond-mat/0703025 |bibcode = 2007Natur.447..295A | s2cid = 4340632 }}</ref>

The latter technique was used to overcome the lack of spin-orbit interaction and materials issues to achieve spin transport in [[silicon]].<ref>{{Cite journal | last1 = Žutić | first1 = I. | last2 = Fabian | first2 = J. | doi = 10.1038/447269a | title = Spintronics: Silicon twists | journal = Nature | volume = 447 | issue = 7142 | pages = 268–269 | year = 2007 | pmid =  17507969|bibcode = 2007Natur.447..268Z | s2cid = 32830840 | doi-access = free }}</ref>

Because external magnetic fields (and stray fields from magnetic contacts) can cause large [[Hall effect]]s and [[magnetoresistance]] in semiconductors (which mimic [[spin-valve]] effects), the only conclusive evidence of spin transport in semiconductors is demonstration of spin [[precession]] and [[dephasing]] in a magnetic field non-collinear to the injected spin orientation, called the [[Hanle effect]].

===Applications===
Applications using spin-polarized electrical injection have shown threshold current reduction and controllable circularly polarized coherent light output.<ref>{{Cite journal | last1 = Holub | first1 = M. | last2 = Shin | first2 = J. | last3 = Saha | first3 = D. | last4 = Bhattacharya | first4 = P. | title = Electrical Spin Injection and Threshold Reduction in a Semiconductor Laser | doi = 10.1103/PhysRevLett.98.146603 | journal = Physical Review Letters | volume = 98 | issue = 14 | year = 2007 | pmid =  17501298|bibcode = 2007PhRvL..98n6603H | page=146603}}</ref> Examples include semiconductor lasers. Future applications may include a spin-based [[transistor]] having advantages over [[MOSFET]] devices such as steeper sub-threshold slope.

'''Magnetic-tunnel transistor''': The magnetic-tunnel transistor with a single base layer<ref name="dijken">{{Cite journal | last1 = Van Dijken | first1 = S. | last2 = Jiang | first2 = X. | last3 = Parkin | first3 = S. S. P. | doi = 10.1063/1.1474610 | title = Room temperature operation of a high output current magnetic tunnel transistor | journal = Applied Physics Letters | volume = 80 | issue = 18 | pages = 3364 | year = 2002 |bibcode = 2002ApPhL..80.3364V }}</ref> has the following terminals:
* Emitter (FM1): Injects spin-polarized hot electrons into the base.
* Base (FM2): Spin-dependent scattering takes place in the base. It also serves as a spin filter.
* Collector (GaAs): A [[Schottky barrier]] is formed at the interface. It only collects electrons that have enough energy to overcome the Schottky barrier, and when states are available in the semiconductor.

The magnetocurrent (MC) is given as:

:<math>MC = \frac{I_{c,p}-I_{c,ap}}{I_{c,ap}}</math>

And the transfer ratio (TR) is

:<math>TR = \frac{I_C}{I_E}</math>

MTT promises a highly spin-polarized electron source at room temperature.

=== Storage media ===
[[Antiferromagnetism|Antiferromagnetic]] storage media have been studied as an alternative to [[ferromagnetism]],<ref>{{cite web |author=Jungwirth, T. |type=announcement of a physics colloquium at a Bavarian university |date=28 April 2014 |title=Relativistic Approaches to Spintronics with Antiferromagnets |url=http://www.physik.uni-regensburg.de/aktuell/KollSS14/Kolloquium-Jungwirth.pdf |access-date=29 April 2014 |archive-date=29 April 2014 |archive-url=https://web.archive.org/web/20140429190040/http://www.physik.uni-regensburg.de/aktuell/KollSS14/Kolloquium-Jungwirth.pdf |url-status=dead }}</ref> especially since with antiferromagnetic material the bits can be stored as well as with ferromagnetic material. Instead of the usual definition 0&nbsp;↔ 'magnetisation upwards', 1&nbsp;↔ 'magnetisation downwards', the states can be, e.g., 0&nbsp;↔ 'vertically alternating spin configuration' and 1&nbsp;↔ 'horizontally-alternating spin configuration'.<ref>This corresponds mathematically to the transition from the rotation group SO(3) to its relativistic covering, the "double group" SU(2)</ref>).

The main advantages of antiferromagnetic material are:

* insensitivity to data-damaging perturbations by stray fields due to zero net external magnetization;<ref name=netzero>{{cite journal |last1=Jungwirth |first1=T. |last2=Marti |first2=X. |last3=Wadley |first3=P. |last4=Wunderlich |first4=J. |title=Antiferromagnetic spintronics |journal=Nature Nanotechnology |publisher=Springer Nature |volume=11 |issue=3 |year=2016 |issn=1748-3387 |doi=10.1038/nnano.2016.18 |pmid=26936817 |pages=231–241 |arxiv=1509.05296|bibcode=2016NatNa..11..231J |s2cid=5058124 }}</ref>
* no effect on near particles, implying that antiferromagnetic device elements would not magnetically disturb its neighboring elements;<ref name=netzero/>
* far shorter switching times (antiferromagnetic resonance frequency is in the THz range compared to GHz ferromagnetic resonance frequency);<ref name =adv>{{cite journal |last1=Gomonay |first1=O. |last2=Jungwirth |first2=T. |last3=Sinova |first3=J. |title=Concepts of antiferromagnetic spintronics |journal=Physica Status Solidi RRL |publisher=Wiley |volume=11 |issue=4 |date=21 February 2017 |issn=1862-6254 |doi=10.1002/pssr.201700022 |page=1700022 |arxiv=1701.06556|bibcode=2017PSSRR..1100022G |s2cid=73575617 }}</ref>
* broad range of commonly available antiferromagnetic materials including insulators, semiconductors, semimetals, metals, and superconductors.<ref name=adv/>

Research is being done into how to read and write information to antiferromagnetic spintronics as their net zero magnetization makes this difficult compared to conventional ferromagnetic spintronics. In modern MRAM, detection and manipulation of ferromagnetic order by magnetic fields has largely been abandoned in favor of more efficient and scalable reading and writing by electrical current. Methods of reading and writing information by current rather than fields are also being investigated in antiferromagnets as fields are ineffective anyway. Writing methods currently being investigated in antiferromagnets are through [[spin-transfer torque]] and [[Spin–orbit interaction|spin-orbit torque]] from the [[spin Hall effect]] and the [[Rashba effect]]. Reading information in antiferromagnets via magnetoresistance effects such as [[tunnel magnetoresistance]] is also being explored.<ref>{{cite journal |last1=Chappert |first1=Claude |last2=Fert |first2=Albert |last3=van Dau |first3=Frédéric Nguyen |title=The emergence of spin electronics in data storage |journal=Nature Materials |publisher=Springer Science and Business Media LLC |volume=6 |issue=11 |year=2007 |issn=1476-1122 |doi=10.1038/nmat2024 |pmid=17972936 |pages=813–823 |bibcode=2007NatMa...6..813C|s2cid=21075877 }}</ref>