Neutron Scattering Studies of Molecule Based Magnets_

 

Talk by Dr. Javier Campo, Aragón Materials Science Institute, (CSIC-University of Zaragoza) Spain.

Neutron Scattering Studies of Molecule Based Magnets

Neutron scattering techniques can provide fundamental insight into the different magnetic behaviors shown by molecule based magnets. In a short introduction the properties of the neutron–matter interactions (strong and magnetic dipolar) and the fundamentals of neutron scattering will be presented in order to facilitate an understanding of the peculiarities of this probe in molecule based magnets. Selected examples will be presented of the use of different neutron scattering techniques on very different molecular magnetic materials. S-based organic magnets. The sulphur based free-radical family p-X-C6F4CNSSN· (X = Br, NO2, CN) represents an alternative to the classical nitrogen-oxygen construct for the design of purely organic magnets.

This example shows how to explore and understand the magnetic interaction mechanisms, via spin density determination using polarized neutron diffraction [1] Single molecule magnets. Single crystal neutron diffraction at very low temperatures and high magnetic field shows how the Mn12-acetate SMM can order via the magnetic dipolar interaction. However, for magnetic fields larger than 5 T it undergoes a quantum phase transition into a zero magnetization phase [2]. The effect of crystal disorder on quantum tunneling in the single-molecule magnet Mn12-benzoate will also be illustrated through measurements of the energy levels using inelastic neutron scattering [3]. Chiral magnets. The control of magnetic chirality in a material could be employed in spintronic devices in order to create or manipulate a spin-current. This example will show how neutron Laue diffraction can help to determine magnetic structures (and therefore the magnetic chirality) in very small crystals of [Cr(CN)6][Mn(S)-pnH(H2O)](H2O) [4]. Spin-crossover magnets. It has proved possible to determine the correlation between the motion of the pyrazine rings and the high-low spin transition in the spin crossover compound {Fe(pz)[Pt(CN)4]} by measuring quasi-elastic neutron scattering [5]. Spin-waves in Heisenberg Antiferromagnets. It is shown how it is possible to determine the magnetic interaction constants in molecular magnets by measuring the spin-wave dispersion curves with neutron triple axis spectroscopy [6].

References

[1] J. Luzón, et al. Phys Rev B. 81(2010) [2] F Luis, J Campo et al. Phys Rev Let 95, 227202 (2005) [3] Ch. Carbonera et al. Phys Rev B 81, 014427 (2010) [4] J Campo et al. submitted [5] J. A. Rodríguez-Velamazán et al. JACS. [6] J. Campo et al, Phys Rev B. 78, 054415 (2008).

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