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Molecular Magnets

Involved people: G. Amoretti, S. Carretta, A. Chiesa, E. Garlatti, P. Santini

Molecules containing magnetically interacting metallic ions have recently become the object of a huge research activity, both from the fundamental point of view and for the potential applications. These molecules are usually arranged in crystalline-ordered structures in which shells of organic ligands provide magnetic separation between adjacent molecules.

The crystal approximately behaves as a collection of identical and non-interacting magnetic particles and single-molecule properties can be probed by bulk measurements.

Molecular nanomagnets (e.g., Fe8 or Mn12) are a class of magnetic molecules displaying hysteresis and slow relaxation of the magnetization at the single-molecule level:

Slow relaxation is associated with the presence of an anisotropy barrier in the single-molecule energy spectrum. The barrier is crossed (and the magnetization relaxes) by a phonon-assisted Orbach process.

This property is potentially useful to design high-density magnetic memories. For example, hard-disk capacity may realistically be increased by a factor larger than 10000 without reaching the so-called superparamagnetic limit.

There are many other classes of magnetic molecules with interesting properties, for example:

Antiferromagnetic rings (e.g., Cr8)

  • Antiferromagnetic n.n. exchange interaction.
  • Nonmagnetic S=0 ground state.
  • One Cr3+ ion can be replaced by a different ion (ground state with S>0).
  • Interesting for fundamental physics (e.g. Néel vector tunneling).
  • Ni-substituted Cr8 : S=1/2, potentially a good candidate qubit.

Grids (e.g., Mn3x3)

  • Antiferromagnetic n.n. exchange interaction.
  • Magnetic S=5/2 ground state.
  • 2d topology.
  • Quantum oscillations of the total molecular spin induced by applied magnetic field.

Thus, magnetic molecules are interesting for both fundamental issues and potential applications:

Fundamental issues:

  • Highly tunable model systems for studying quantum phenomena (quantum tunneling, coherence, quantum-classical crossover, etc.), and to study microscopic magnetic interactions

Main potential applications:

  • High-density information storage with nanomagnets
  • Quantum computation
  • Magnetocaloric refrigerants

Our activities:

We have a PRIN project running and we are part of the MAGMAnet EU network of excellence, which incorporates the most important EU groups of physicists and chemists working on magnetic molecules. We work in close contact with several of these groups, in particular on:

  • Theoretical modelling of coherent and relaxation dynamics by microscopic Hamiltonians. Modelling of macroscopic, NMR, muSR experimental results.
  • Inelastic neutron scattering : experiments and modelling.
  • Identification and study of molecules suitable for quantum computation.
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Page last modified on October 23, 2013, at 10:58 AM