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Phys. Rev. Lett. 94, 017205 (2005) [4 pages]

Competing Spin Phases in Geometrically Frustrated Magnetic Molecules

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Christian Schröder*
Department of Electrical Engineering and Computer Science, University of Applied Sciences Bielefeld, D-33602 Bielefeld, Germany and Ames Laboratory, Ames, Iowa 50011, USA

Hiroyuki Nojiri
Department of Physics, Okayama University, Tsushimanaka 3-1-1, Okayama, 700-8530 Japan

Jürgen Schnack and Peter Hage
Fachbereich Physik, Universität Osnabrück, D-49069 Osnabrück, Germany

Marshall Luban and Paul Kögerler
Ames Laboratory & Department of Physics and Astronomy, Iowa State University, Ames, Iowa 50011, USA

Received 18 May 2004; revised 27 November 2004; published 11 January 2005

We identify a class of zero-dimensional classical and quantum Heisenberg spin systems exhibiting anomalous behavior in an external magnetic field B similar to that found for the geometrically frustrated kagome lattice of classical spins. Our calculations for the isotropic Heisenberg model show the emergence of a pronounced minimum in the differential susceptibility dM/dB at Bsat/3 as the temperature T is raised from 0 K for structures based on corner-sharing triangles, specifically the octahedron, cuboctahedron, and icosidodecahedron. As the first experimental evidence we note that the giant Keplerate magnetic molecule {Mo72Fe30} (Fe3+ ions on the 30 vertices of an icosidodecahedron) exhibits this behavior. For low T when B≈Bsat/3 two competing families of spin configurations exist of which one behaves magnetically “stiff” leading to a reduction of dM/dB.

© 2005 The American Physical Society

URL:
http://link.aps.org/doi/10.1103/PhysRevLett.94.017205
DOI:
10.1103/PhysRevLett.94.017205
PACS:
75.50.Xx, 75.10.Hk, 75.10.Jm, 75.40.Cx

*Electronic address: schroder@ameslab.gov

 
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