2009年04月08日

Twist

The spins of a layer of manganese atoms on a tungsten surface from appairal pattern with a unique turning sense. such 'chiral magnetic order' might exist in other, similar contects.

Chirality is a fasinating phenomenon that can manifest itself in subtle ways, for example in biochemistry (in the observed single-handedness of biomolecules) and in particle physis (in the chage-parity violation of electroweak in teractions). (Siegel,J.S. Single-handed cooperation. Nature 409,777-778/2001)(Ellis,J. Antimatter matters. Nature 424,631-634/2003)

In condensed matter, magnetic materials canalso display single-handed, or homochiral, spin tructures. This may be coused by the Dzyaloshinskkii-Moeiya interction, wichi arises from spin-orbit scattering of electrons in an inversion-asymmetric crystal field.(Dzialoshinskii,I.E. Thermodynamic theory of "Weak" ferromagnetism in antiferromagnetic substances. Sov Phys. JETP 5,1259-1262/1957)(Moriya,T. Anistotropic superexchange interaction and weak ferromagetism. phys.Rev. 120,91-98/1960)

This effect is typically irrelevant in bulk metals as their crystals are inversion symmetric. However, low-dimensional systems lack structural inversion summetry, so that homochiral spin structures may occur.(Fert,A. Magnetic and transport properties of metallic multilayers. Mater. Aci froum 59&60, 439-443/1990)

### data ###
Nature 447,115-230 / 2007
Let's twist again / Cristian Pfleiderer and Ulich K. RoBler
Chiral magnetic order at surfaces driven by inversion asymmetry / M Bode et al (University of Hamburg)
posted by 0≠素子 at 09:16| Comment(0) | condensed-matter physics | このブログの読者になる | 更新情報をチェックする

2009年03月03日

CONDENSED-MATTER PHYSICS : Let's twist agein

The spins of a layer of manganese atoms on a tungusten surface from a spiral pattern with a unique truning sense.

such 'chirial maganitic order' might exist in other, similar contexts, and have many useful applications.


Objects that differ from their mirror image - fuman hands, for instance - have a turn ing sense. This phenomenon of handedness, or chirality, is found in many natural contexts, from the elementary particles participating in electroweak interactions, via organic molecules and furricanes, all the way to galaxies.

Solids with a magnetic order of unique chirality could have many useful practical applications, becouse their peculiar symmetry allows the mixing of electronic, optical, magnetic and structural properties.

On page 190 of this isse, Bode et al. present compelling evidence for chiral magnetic order in a atrikingly simple solid-state system : a single layer of manganese atoms on a tungsten substrate.(Bode,M. et al. Nature 447,190-193/2007)

The authors achieved this by combining highly sophisticated, spin-sensitive scanning tunnelling micros-copy (STM) with an equally sophisticated first-principles calculation of the electronic structure of the manganese surface.

The amount of electrical current tunnelling from the manganese sample to the authors 'STM tip, which was coated with chromium or iron, depended on the electrons' derection of spin.

What Bode et al. observed was a long-period, spiral-shaped magnetic modulation of the STM intensity distoribution, superimposed on a basic antiferromagnetic structure (one in which adjacent spins point in opposite directions) .

When a magnetic field was applied, the pattern shifted in a given direction, identifying its unique chirality.


### DataBace ###
nature Vol.447 115-230 Issue no.7141 10 May 2007
News & Views p.157 /CONDENSED-MATTER PHYSICS : Let's twist agein / Cristien Pfleiderer and Urich K Robler
Letter p.190 / Chiral magnetic order at surfaces driven by inversion asymmetry / M Bode et al. (University of Hambrg)

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