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Half-Integer Spin Molecular Nanomagnets

Published online by Cambridge University Press:  10 February 2011

David N. Hendrickson
Affiliation:
Department of Chemistry and Biochemistry-0358, University of California at San Diego, La Jolla, California 92093–0358, U.S.A.
George Christou
Affiliation:
Department of Chemistry, University of Florida, Gainesville, Florida 32611–7200, U.S.A.
Wolfgang Wernsdorfer
Affiliation:
L. Néel-CNRS, BP 166, 25 Avenue des Martyrs, 38042 Grenoble, Cedex 9, France.
Stephen O. Hill
Affiliation:
Department of Physics, University of Florida, Gainesville, Florida 32611, U.S.A.
Núria Aliaga-Alcade
Affiliation:
Department of Chemistry, University of Florida, Gainesville, Florida 32611–7200, U.S.A.
Sumit Bhaduri
Affiliation:
Department of Chemistry, University of Florida, Gainesville, Florida 32611–7200, U.S.A.
Rachel S. Edwards
Affiliation:
Department of Physics, University of Florida, Gainesville, Florida 32611, U.S.A.
Sheila M. J. Aubin
Affiliation:
Department of Chemistry and Biochemistry-0358, University of California at San Diego, La Jolla, California 92093–0358, U.S.A.
Ziming Sun
Affiliation:
Department of Chemistry and Biochemistry-0358, University of California at San Diego, La Jolla, California 92093–0358, U.S.A.
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Abstract

Single-molecule magnets (SMM) are molecules that function as single-domain nanomagnets. SMMs have been characterized with a ground-state spin ranging from S = 4 to S = 13. A few SMMs have been identified that have half-integer spin ground states. [Cation][Mn12O12(O2CR)16(H2O)4] complexes, where R is some substituent, are SMMs that have either a S = 19/2 or 21/2 ground state. Quantum tunneling of magnetization (QTM) is observed for these half-integer-spin Kramers [Mn12]- degenerate SMMs in zero external magnetic field, as well as for a class of S = 9/2 Mn4 SMMs. The presence of QTM in zero external field is attributed to a transverse component of a nuclear spin field, dipolar interactions and intermolecular exchange interactions. The Landau-Zener method is used to measure the tunnel splitting as a function of transverse magnetic field for a single crystal of the S = 9/2 SMM [Mn4O3(OSiMe3)(OAc)3(dbm)3]. Spin parity dependent QTM is established. The effect of a magnetic exchange interaction between two S = 9/2 Mn4 SMMs upon QTM was studied for another compound. The hydrogen bonding and Cl…Cl contacts within a supramolecularly linked [Mn4]2 dimer lead to a weak antiferromagnetic exchange interaction between the two S = 9/2 SMMs. This interaction causes a shift (exchange bias) from zero field for the magnetic field at which QTM occurs.

Type
Research Article
Copyright
Copyright © Materials Research Society 2003

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