Semiconductive and Photoconductive Properties of the Single Molecule Magnets Mn${}_{12}$-Acetate and Fe${}_8$Br${}_8$

Abstract

Resistivity measurements are reported for single crystals of Mn${}_{12}$-Acetate and Fe${}_8$Br${}_8$. Both materials exhibit a semiconductor-like, thermally activated behavior over the 200-300 K range. The activation energy, $E_a$, obtained for Mn${}_{12}$-Acetate was 0.37 $\pm$ 0.05 eV, which is to be contrasted with the value of 0.55 eV deduced from the earlier reported absorption edge measurements and the range of 0.3-1 eV from intramolecular density of states calculations, assuming $2E_a$= $E_g$, the optical band gap. For Fe${}_8$Br${}_8$, $E_a$ was measured as 0.73 $\pm$ 0.1 eV, and is discussed in light of the available approximate band structure calculations. Some plausible pathways are indicated based on the crystal structures of both lattices. For Mn${}_{12}$-Acetate, we also measured photoconductivity in the visible range; the conductivity increased by a factor of about eight on increasing the photon energy from 632.8 nm (red) to 488 nm (blue). X-ray irradiation increased the resistivity, but $E_a$ was insensitive to exposure.

7 pages, 8 figures

References in corpus (10)

• Effects of D-strain, g-strain, and dipolar interactions on EPR linewidths of the molecular magnets Fe8 and Mn12
• Detailed single crystal EPR lineshape measurements for the single molecule magnets Fe8Br and Mn12-ac
• Spin tunneling via dislocations in Mn-12 acetate crystals
• Crossover between Thermally Assisted and Pure Quantum Tunneling in Molecular Magnet Mn12-Acetate
• Dislocation-induced spin tunneling in Mn-12 acetate
• 55Mn NMR in Mn12 acetate: Hyperfine interaction and magnetic relaxation of cluster
• Magnetic Field Effects on the Far-Infrared Absorption in Mn_12-acetate
• Photo-response of the conductivity in functionalized pentacene compounds
• Electron Paramagnetic Resonance Linewidths and Lineshapes for the Molecular Magnets Fe8 and Mn12
• On Ground State Tunneling in Mn${}_{12}$-Acetate

Cited by in corpus (6)

• Properties of low-lying excited manifolds in the Mn12 acetate
• Effect of extra electrons on the exchange and magnetic anisotropy in the anionic single-molecule magnet Mn12
• First-principles modelling of magnetic excitations in Mn12
• Tight Binding Model of Mn12 Single Molecule Magnets: Electronic and Magnetic Structure and Transport Properties
• Ligand-based transport resonances of single-molecule magnet spin filters: Suppression of the Coulomb blockade and determination of the orientation of the magnetic easy axis
• Correlation effects in the electronic structure of Mn${}_4$ molecular magnet