Nanomagnet

A nanomagnet is a submicrometric 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.

Attending to the number of magnetic atoms, the smallest nanomagnets reported so far are double decker phthalocyanes with only one rare earth atom.[4] 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:

  1. A ground state with finite spin
  2. A magnetic anisotropy energy barrier
  3. Long spin relaxation time.

Conditions 1 and 2, but not 3, have been demonstrated in a number of nanostructures, such as nanoparticles,[5] nanoislands,[6] and quantum dots[7][8] with a controlled number of magnetic atoms (between 1 and 10).

A nanomagnet can have enhanced electronic properties due to size effect, such as long spin relaxation time of conduction electron, which may be useful for nano-scale spintronic device.[9]

References

  1. ↑ S. Guéron et al., Tunneling vis Individual Electronic States in Ferromagnetic Nanoparticles, Phys. Rev. Lett. 83, 4148 (1999)
  2. ↑ M. Jamet et al., Magnetic Anisotropy of a Single Cobalt Nanocluster Phys. Rev. Lett 86. 4676 (2001).
  3. ↑ Molecular Nanomagnets, Dante Gatteschi, Roberta Sessoli, Jacques Villain Oxford University Press, 2006 ISBN 0-19-856753-7
  4. ↑ N. Ishikawa, M. Sugita, W. Wernsdorfer J. Am. Chem. Soc. 127, 3650 (2005)
  5. ↑ P. Gambardella et al., Giant magnetic anisotropy of single Co atoms and nanoparticles, Science 300, 1130 (2003),
  6. ↑ C. F. Hirjibehedin, C. P. Lutz, and A. J. Heinrich, Spin Coupling in Engineered Atomic Structures. Science 312, 1021 (2006)
  7. ↑ Y. Leger et al., Electrical Control of a Single Mn atom in a Quantum Dot Phys. Rev. Lett. 97, 107401(2006)
  8. ↑ A. Kudelski, A. Lemaître, A. Miard, P. Voisin, T. C. M. Graham, R. J. Warburton, and O. Krebs, Optically Probing the Fine Structure of a Single Mn Atom in an InAs Quantum Dot, Phys. Rev. Lett. 99, 247209 (2007)
  9. ↑ P. N. Hai, S. Ohya, and M. Tanaka,Long spin-relaxation time in a single metal nanoparticle, Nature Nanotechnology 5, 593–596 (2010)

Further reading


This article is issued from Wikipedia - version of the Saturday, November 28, 2015. The text is available under the Creative Commons Attribution/Share Alike but additional terms may apply for the media files.