Magnetic Relaxation Study on Single Crystals of Ni4 Single-Molecule Magnets

  • The ac susceptibility of single crystals of Ni4 single-molecule magnets is measured by a compensation measurement setup. The magnetic relaxation time calculated from the peak of the out-phase component of the susceptibility fits the Arrhenius law well and gives an effective spin-flipping energy barrier of Ueff=7.2K. This value is far below the classical activation energy barrier of U=14K, whereas it is close to the energy gap between the Sz=±4 and Sz=±3 doublets, which indicates that quantum tunneling between the Sz=3 and Sz=-3 states plays a key role in the magnetic relaxation. Therefore the relaxation process combines thermal activation and quantum tunneling. Also we deduce that the blocking temperature of Ni4 single-molecule magnets is lower than 0.3K by extrapolating the relaxation time plot, which ensures that this single-molecule magnet material enters a long-range magnetic ordered state instead of a spin glass state at 0.91K.
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