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Hysteresis and resonant MQT

Hysteresis and resonant MQT. Resonant quantum tunneling. B// z. Note: resonant tunneling strong at B = 0. Hysteresis and resonant MQT. Resonant tunneling. The hysteresis is a property of each single molecule. Hysteresis loops of Mn 4 single-molecule magnets.

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Hysteresis and resonant MQT

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  1. Hysteresis and resonant MQT Resonant quantum tunneling B//z Note: resonant tunneling strong at B = 0

  2. Hysteresis and resonant MQT Resonant tunneling The hysteresis is a property of each single molecule

  3. Hysteresis loops ofMn4 single-molecule magnets Mn4O3(OSiMe3)(O2CMe)3(dbm)3 [Mn4(O2CMe)2(Hpdm)6][ClO4]2 S = 9/2 S = 8

  4. Kramers theorem: No matter how unsymmetric the crystal field, a system possessing an odd number of electrons must have a ground state that is at least doubly degenerate, even in the presence of crystal fields and spin-orbit interactions H. A. Kramers, Proc. Acad. Sci. Amsterdam 33, 959 (1930) Mesoscopic systems: J.L. Van Hemmen and S. Süto, Europhys. Lett. 1, 481 (1986) D. Loss, D.P. DiVincenzo, and G. Grinstein, Phys. Rev. Lett., 69, 3232 (1992) J. von Delft and C. L. Hendey, Phys. Rev. Lett., 69, 3236 (1992) Spin-parity dependent quantum tunneling

  5. Spin-parity dependent quantum tunneling Environnemental effects • hyperfine interaction (nuclear spins) • dipolar interaction between molecules • exchange interaction between molecules etc.

  6. Interests in Single Molecule Magnets • As single molecule magnetic memory devices • As magnetic quantum logic devices • Fundamental studies of large spins, i.e. quantum vs. classical behavior • Studies of dynamics of nanomagnets • Studies of quantum decoherence (environmental couplings) • Advantages: • Monodisperse magnetic unit • Chemical control - "bottom-up" materials engineering • Tremendous control of the magnetic unit (the spin), as well as its coupling to the environment • Michael N. Leuenberger and Daniel Loss, Nature 410, 789 (2001).

  7. HIGH FREQUENCY EPR

  8. Energy level diagram for D < 0 system Note frequency range B // z-axis of molecule

  9. Cavity perturbation Cylindrical TE01n (Q~104 -105) f = 16  250 GHz Single crystal 0.2×0.2×0.1 mm3 T = 0.5 to 300 K, B up to 45 tesla q M. Mola et al., Rev. Sci. Inst. 71, 186 (2000)

  10. More on the technique • We use a Millimeter-wave Vector Network Analyzer (MVNA, ABmm) as a spectrometer. • This device allows vector measurements with continuous frequency coverage from 8 to 600 GHz. • We currently use cavities up to 250 GHz and have a reflectivity probe working up to 450 GHz. • We use over-moded cavities when closely spaced frequencies are required. • A 3He capability has just been successfully tested. • The cavity technique, in combination with the vector capability, is extremely important for line shape analysis; eliminates many instrumental effects which plague single-pass scalar measurements. • S. Hill, S. Maccagnano, K. Park, R. M. Achey, J. M. North and N. S. Dalal, Phys. Rev. B 65, 224410 (2002). • M. Mola et al., Rev. Sci. Inst. 71, 186 (2000).

  11. Energy level diagram for S = 9/2, D < 0 system B // z-axis of molecule

  12. HFEPR for high symmetry (C3v) Mn4 cubane Inhomogeneous lineshape Field // z-axis of the molecule (±0.2o)

  13. Fit to easy axis data - yields diagonal crystal field terms

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