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Internal Degrees of Freedom and Quantum Tunneling of the Magnetization

Internal Degrees of Freedom and Quantum Tunneling of the Magnetization in Single-Molecule Magnets. E NRIQUE DEL B ARCO. Department of Physics – UCF Orlando. In collaboration with: Steve Hill (FSU & NHMFL ) and David N. Hendrickson (UCSD). SPONSORED BY:. OUTLINE.

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Internal Degrees of Freedom and Quantum Tunneling of the Magnetization

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  1. Internal Degrees of Freedom and Quantum Tunneling of the Magnetization in Single-Molecule Magnets ENRIQUE DEL BARCO Department of Physics – UCF Orlando In collaboration with: Steve Hill (FSU&NHMFL) and David N. Hendrickson (UCSD) SPONSORED BY:

  2. OUTLINE SMMs and Giant Spin Approximation GSA failure / multi-spin description / low-nuclearity SMMs A low nuclearity SMM: Mn4 EPR and QTM Characterization Asymmetric Berry Phase Interference Symmetry Considerations Motion of Berry Phase Patterns Internal Degrees of Freedom

  3. SMMs and the GSA MODEL 8MnIII(S=2) = 16 ~ S = 10 -4MnIV(S=3/2) = 6

  4. SMMs and the GSA MODEL ~ S = 10 z up y x down

  5. SMMs and the GSA MODEL Magnetic field ~ S = 10 z up y x down

  6. SMMs and the GSA MODEL ~ S = 10 z up y x down on-resonance off-resonance QT on (fast relaxation) on-resonance QT off (non relaxation)

  7. SMMs and the GSA MODEL

  8. FAILURE of the GSA MODEL Anomalous term Low-lying excited states QTM btw. different spin lengths Ramsey et al. (2008) observed before in AF molecules Carreta et al. (2007) Mukhin et al. (2001) Barra et al. (1997)

  9. MULTI-SPIN DESCRIPTION LOW NUCLEARITY SMMs Mn3 (S = 2,6) Mn6 (S = 4,12) Ni4 (S = 4) Connection between Dmol and dion Higher-order molecular anisotropy Consequences of weak coupling and spin frustration Internal degrees of freedom and QTM: (Symmetry lowering effects) (Spin selection rules) S. Hill et al., Dalton Transactions (2010).

  10. MULTI-SPIN DESCRIPTION THE CASE OF Mn4 SMM MnIII (S = 2) MnII (S = 5/2) S = 9 (at low-T) [Mn4(Bet)4(mdea)4(Hmdea)2] (BPh4)4 K. J. Heroux et al., unpublished.

  11. MULTI-SPIN DESCRIPTION THE CASE OF Mn4 SMM

  12. MULTI-SPIN DESCRIPTION THE CASE OF Mn4 SMM test: k=1? ( )

  13. MULTI-SPIN DESCRIPTION THE CASE OF Mn4 SMM ( )

  14. MULTI-SPIN DESCRIPTION THE CASE OF Mn4 SMM TIME REVERSAL INVARIANCE OF THE SPIN-ORBIT INTERACTION =ODD =EVEN =ODD =EVEN =ODD

  15. MULTI-SPIN DESCRIPTION THE CASE OF Mn4 SMM Second order anisotropy (symmetries): 3 mutually orthogonal two-fold rotation axes 3 mutually orthogonal mirror planes Inversion center (b) Guarantees invariance w.r.t. reversal of HT IMPOSES SYMMETRIC BPI PATTERNS WHETHER HL=0 or HL0 xy-mirror symmetry must be broken TO ALLOW ASYMMETRIC BPI PATTERNS W.R.T. HT REVERSAL TRI GUARANTEES THE TWO PATTERNS TO BE MIRROR IMAGES

  16. MULTI-SPIN DESCRIPTION THE CASE OF Mn4 SMM

  17. MULTI-SPIN DESCRIPTION Euler angles:

  18. MULTI-SPIN DESCRIPTION CENTRAL ION (2) (z - easy axis) (x - hard axis) EXTERNAL IONS (1,3)

  19. SOME RELAXATION ISSUES

  20. SOME RELAXATION ISSUES

  21. SOME RELAXATION ISSUES

  22. SOME RELAXATION ISSUES

  23. ACKNOWLEDGEMENTS STUDENTS: Hajrah M. Quddusi and Simran Singh (UCF) Junjie Liu (FSU) Katie Heroux and Chris Beedle (UCSD)

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