In magnetism, a nanomagnet is a nanoscopic scale system that presents spontaneous magnetic order ( magnetization) at zero applied magnetic field ( remanence).
The small size of nanomagnets prevents the formation of magnetic domains (see single domain (magnetic)). The magnetization dynamics of sufficiently small nanomagnets at low temperatures, typically single-molecule magnets, presents quantum phenomena, such as macroscopic spin tunnelling. At larger temperatures, the magnetization undergoes random thermal fluctuations ( superparamagnetism) which present a limit for the use of nanomagnets for permanent information storage.
Canonical examples of nanomagnets are grains [1] [2] of ferromagnetic metals ( iron, cobalt, and nickel) and single-molecule magnets. [3] The vast majority of nanomagnets feature transition metal ( titanium, vanadium, chromium, manganese, iron, cobalt or nickel) or rare earth ( Gadolinium, Europium, Erbium) magnetic atoms.
The ultimate limit in miniaturization of nanomagnets was achieved in 2016: individual Ho atoms present remanence when deposited on an atomically thin layer of MgO coating a silver film was reported by scientists from EPFL and ETH, in Switzerland. [4] Before that, the smallest nanomagnets reported, attending to the number of magnetic atoms, were double decker phthalocyanes molecules with only one rare-earth atom. [5] Other systems presenting remanence are nanoengineered Fe chains, deposited on Cu2N/Cu(100) surfaces, showing either Neel [6] or ferromagnetic ground states [7] with in systems with as few as 5 Fe atoms with S=2. Canonical single-molecule magnets are the so-called Mn12 and Fe8 systems, with 12 and 8 transition metal atoms each and both with spin 10 (S = 10) ground states.
The phenomenon of zero field magnetization requires three conditions:
- A ground state with finite spin
- A magnetic anisotropy energy barrier
- Long spin relaxation time.
Conditions 1 and 2, but not 3, have been demonstrated in a number of nanostructures, such as nanoparticles, [8] nanoislands, [9] and quantum dots [10] [11] with a controlled number of magnetic atoms (between 1 and 10).
References
- ^ Guéron, S.; Deshmukh, Mandar M.; Myers, E. B.; Ralph, D. C. (15 November 1999). "Tunneling via Individual Electronic States in Ferromagnetic Nanoparticles". Physical Review Letters. 83 (20): 4148–4151. arXiv: cond-mat/9904248. Bibcode: 1999PhRvL..83.4148G. doi: 10.1103/PhysRevLett.83.4148. S2CID 39584741.
- ^ Jamet, M.; Wernsdorfer, W.; Thirion, C.; Mailly, D.; Dupuis, V.; Mélinon, P.; Pérez, A. (14 May 2001). "Magnetic Anisotropy of a Single Cobalt Nanocluster". Physical Review Letters. 86 (20): 4676–4679. arXiv: cond-mat/0012029. Bibcode: 2001PhRvL..86.4676J. doi: 10.1103/PhysRevLett.86.4676. PMID 11384312. S2CID 41734831.
- ^ Gatteschi, Dante; Sessoli, Roberta; Villain, Jacques (2006). Molecular Nanomagnets (Reprint ed.). New York: Oxford University Press. ISBN 0-19-856753-7.
- ^ Donati, F.; Rusponi, S.; Stepanow, S.; Wäckerlin, C.; Singha, A.; Persichetti, L.; Baltic, R.; Diller, K.; Patthey, F. (2016-04-15). "Magnetic remanence in single atoms". Science. 352 (6283): 318–321. Bibcode: 2016Sci...352..318D. doi: 10.1126/science.aad9898. hdl: 11590/345616. ISSN 0036-8075. PMID 27081065. S2CID 30268016.
- ^ Ishikawa, Naoto; Sugita, Miki; Wernsdorfer, Wolfgang (March 2005). "Nuclear Spin Driven Quantum Tunneling of Magnetization in a New Lanthanide Single-Molecule Magnet: Bis(Phthalocyaninato)holmium Anion". Journal of the American Chemical Society. 127 (11): 3650–3651. arXiv: cond-mat/0506582. Bibcode: 2005cond.mat..6582I. doi: 10.1021/ja0428661. PMID 15771471. S2CID 40136392.
- ^ Loth, Sebastian; Baumann, Susanne; Lutz, Christopher P.; Eigler, D. M.; Heinrich, Andreas J. (2012-01-13). "Bistability in Atomic-Scale Antiferromagnets". Science. 335 (6065): 196–199. Bibcode: 2012Sci...335..196L. doi: 10.1126/science.1214131. ISSN 0036-8075. PMID 22246771. S2CID 128108.
- ^ Spinelli, A.; Bryant, B.; Delgado, F.; Fernández-Rossier, J.; Otte, A. F. (2014-08-01). "Imaging of spin waves in atomically designed nanomagnets". Nature Materials. 13 (8): 782–785. arXiv: 1403.5890. Bibcode: 2014NatMa..13..782S. doi: 10.1038/nmat4018. ISSN 1476-1122. PMID 24997736.
- ^ Gambardella, P. (16 May 2003). "Giant Magnetic Anisotropy of Single Cobalt Atoms and Nanoparticles". Science. 300 (5622): 1130–1133. Bibcode: 2003Sci...300.1130G. doi: 10.1126/science.1082857. PMID 12750516. S2CID 5559569.
- ^ Hirjibehedin, C. F. (19 May 2006). "Spin Coupling in Engineered Atomic Structures". Science. 312 (5776): 1021–1024. Bibcode: 2006Sci...312.1021H. doi: 10.1126/science.1125398. PMID 16574821. S2CID 24061939.
- ^ Léger, Y.; Besombes, L.; Fernández-Rossier, J.; Maingault, L.; Mariette, H. (7 September 2006). "Electrical Control of a Single Mn Atom in a Quantum Dot" (PDF). Physical Review Letters. 97 (10): 107401. Bibcode: 2006PhRvL..97j7401L. doi: 10.1103/PhysRevLett.97.107401. hdl: 10045/25252. PMID 17025852.
- ^ Kudelski, A.; Lemaître, A.; Miard, A.; Voisin, P.; Graham, T. C. M.; Warburton, R. J.; Krebs, O. (14 December 2007). "Optically Probing the Fine Structure of a Single Mn Atom in an InAs Quantum Dot". Physical Review Letters. 99 (24): 247209. arXiv: 0710.5389. Bibcode: 2007PhRvL..99x7209K. doi: 10.1103/PhysRevLett.99.247209. PMID 18233484. S2CID 16664854.
Further reading
- Friedman, J. R.; Sarachik, M. P. (2010). "Single-Molecule Nanomagnets". Annual Review of Condensed Matter Physics. 1: 109–128. arXiv: 1001.4194. Bibcode: 2010ARCMP...1..109F. doi: 10.1146/annurev-conmatphys-070909-104053. S2CID 118713965.
 | This electromagnetism-related article is a stub. You can help Wikipedia by expanding it. |
In magnetism, a nanomagnet is a nanoscopic scale system that presents spontaneous magnetic order ( magnetization) at zero applied magnetic field ( remanence).
The small size of nanomagnets prevents the formation of magnetic domains (see single domain (magnetic)). The magnetization dynamics of sufficiently small nanomagnets at low temperatures, typically single-molecule magnets, presents quantum phenomena, such as macroscopic spin tunnelling. At larger temperatures, the magnetization undergoes random thermal fluctuations ( superparamagnetism) which present a limit for the use of nanomagnets for permanent information storage.
Canonical examples of nanomagnets are grains [1] [2] of ferromagnetic metals ( iron, cobalt, and nickel) and single-molecule magnets. [3] The vast majority of nanomagnets feature transition metal ( titanium, vanadium, chromium, manganese, iron, cobalt or nickel) or rare earth ( Gadolinium, Europium, Erbium) magnetic atoms.
The ultimate limit in miniaturization of nanomagnets was achieved in 2016: individual Ho atoms present remanence when deposited on an atomically thin layer of MgO coating a silver film was reported by scientists from EPFL and ETH, in Switzerland. [4] Before that, the smallest nanomagnets reported, attending to the number of magnetic atoms, were double decker phthalocyanes molecules with only one rare-earth atom. [5] Other systems presenting remanence are nanoengineered Fe chains, deposited on Cu2N/Cu(100) surfaces, showing either Neel [6] or ferromagnetic ground states [7] with in systems with as few as 5 Fe atoms with S=2. Canonical single-molecule magnets are the so-called Mn12 and Fe8 systems, with 12 and 8 transition metal atoms each and both with spin 10 (S = 10) ground states.
The phenomenon of zero field magnetization requires three conditions:
- A ground state with finite spin
- A magnetic anisotropy energy barrier
- Long spin relaxation time.
Conditions 1 and 2, but not 3, have been demonstrated in a number of nanostructures, such as nanoparticles, [8] nanoislands, [9] and quantum dots [10] [11] with a controlled number of magnetic atoms (between 1 and 10).
References
- ^ Guéron, S.; Deshmukh, Mandar M.; Myers, E. B.; Ralph, D. C. (15 November 1999). "Tunneling via Individual Electronic States in Ferromagnetic Nanoparticles". Physical Review Letters. 83 (20): 4148–4151. arXiv: cond-mat/9904248. Bibcode: 1999PhRvL..83.4148G. doi: 10.1103/PhysRevLett.83.4148. S2CID 39584741.
- ^ Jamet, M.; Wernsdorfer, W.; Thirion, C.; Mailly, D.; Dupuis, V.; Mélinon, P.; Pérez, A. (14 May 2001). "Magnetic Anisotropy of a Single Cobalt Nanocluster". Physical Review Letters. 86 (20): 4676–4679. arXiv: cond-mat/0012029. Bibcode: 2001PhRvL..86.4676J. doi: 10.1103/PhysRevLett.86.4676. PMID 11384312. S2CID 41734831.
- ^ Gatteschi, Dante; Sessoli, Roberta; Villain, Jacques (2006). Molecular Nanomagnets (Reprint ed.). New York: Oxford University Press. ISBN 0-19-856753-7.
- ^ Donati, F.; Rusponi, S.; Stepanow, S.; Wäckerlin, C.; Singha, A.; Persichetti, L.; Baltic, R.; Diller, K.; Patthey, F. (2016-04-15). "Magnetic remanence in single atoms". Science. 352 (6283): 318–321. Bibcode: 2016Sci...352..318D. doi: 10.1126/science.aad9898. hdl: 11590/345616. ISSN 0036-8075. PMID 27081065. S2CID 30268016.
- ^ Ishikawa, Naoto; Sugita, Miki; Wernsdorfer, Wolfgang (March 2005). "Nuclear Spin Driven Quantum Tunneling of Magnetization in a New Lanthanide Single-Molecule Magnet: Bis(Phthalocyaninato)holmium Anion". Journal of the American Chemical Society. 127 (11): 3650–3651. arXiv: cond-mat/0506582. Bibcode: 2005cond.mat..6582I. doi: 10.1021/ja0428661. PMID 15771471. S2CID 40136392.
- ^ Loth, Sebastian; Baumann, Susanne; Lutz, Christopher P.; Eigler, D. M.; Heinrich, Andreas J. (2012-01-13). "Bistability in Atomic-Scale Antiferromagnets". Science. 335 (6065): 196–199. Bibcode: 2012Sci...335..196L. doi: 10.1126/science.1214131. ISSN 0036-8075. PMID 22246771. S2CID 128108.
- ^ Spinelli, A.; Bryant, B.; Delgado, F.; Fernández-Rossier, J.; Otte, A. F. (2014-08-01). "Imaging of spin waves in atomically designed nanomagnets". Nature Materials. 13 (8): 782–785. arXiv: 1403.5890. Bibcode: 2014NatMa..13..782S. doi: 10.1038/nmat4018. ISSN 1476-1122. PMID 24997736.
- ^ Gambardella, P. (16 May 2003). "Giant Magnetic Anisotropy of Single Cobalt Atoms and Nanoparticles". Science. 300 (5622): 1130–1133. Bibcode: 2003Sci...300.1130G. doi: 10.1126/science.1082857. PMID 12750516. S2CID 5559569.
- ^ Hirjibehedin, C. F. (19 May 2006). "Spin Coupling in Engineered Atomic Structures". Science. 312 (5776): 1021–1024. Bibcode: 2006Sci...312.1021H. doi: 10.1126/science.1125398. PMID 16574821. S2CID 24061939.
- ^ Léger, Y.; Besombes, L.; Fernández-Rossier, J.; Maingault, L.; Mariette, H. (7 September 2006). "Electrical Control of a Single Mn Atom in a Quantum Dot" (PDF). Physical Review Letters. 97 (10): 107401. Bibcode: 2006PhRvL..97j7401L. doi: 10.1103/PhysRevLett.97.107401. hdl: 10045/25252. PMID 17025852.
- ^ Kudelski, A.; Lemaître, A.; Miard, A.; Voisin, P.; Graham, T. C. M.; Warburton, R. J.; Krebs, O. (14 December 2007). "Optically Probing the Fine Structure of a Single Mn Atom in an InAs Quantum Dot". Physical Review Letters. 99 (24): 247209. arXiv: 0710.5389. Bibcode: 2007PhRvL..99x7209K. doi: 10.1103/PhysRevLett.99.247209. PMID 18233484. S2CID 16664854.
Further reading
- Friedman, J. R.; Sarachik, M. P. (2010). "Single-Molecule Nanomagnets". Annual Review of Condensed Matter Physics. 1: 109–128. arXiv: 1001.4194. Bibcode: 2010ARCMP...1..109F. doi: 10.1146/annurev-conmatphys-070909-104053. S2CID 118713965.
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