title: Competing spin phases in geometrically frustrated magnetic molecules.
abstract: 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 B(sat)/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 {Mo(72)Fe(30)} (Fe(3+) ions on the 30 vertices of an icosidodecahedron) exhibits this behavior. For low T when B approximately B(sat)/3 two competing families of spin configurations exist of which one behaves magnetically "stiff" leading to a reduction of dM/dB.
authors.affiliation: Department of Electrical Engineering and Computer Science, University of Applied Sciences Bielefeld, D-33602 Bielefeld, Germany. schroder@ameslab.gov
authors.forename: Christian
authors.initials: C
authors.lastname: Schröder
authors.forename: Hiroyuki
authors.initials: H
authors.lastname: Nojiri
authors.forename: Jürgen
authors.initials: J
authors.lastname: Schnack
authors.forename: Peter
authors.initials: P
authors.lastname: Hage
authors.forename: Marshall
authors.initials: M
authors.lastname: Luban
authors.forename: Paul
authors.initials: P
authors.lastname: Kögerler