1. Spin Dynamics and Magnetic Properties of Molecular Magnets
Byoung Jin Suh
The Catholic University of Korea
NMR 1/T1 in AF Coupled Molecular Clusters
Magnetization in Mn12-Ac, Mn12-PrCl, Mn12-BuCl
Magnetization in Artificially Engineered Ferritins

2. Spin Dynamics Ames Lab. Iowa State Univ. Prof. F. Borsa Prof. M. Luban
Dr. D. Procissi
Dr. P. Kögerler
Dr. A. Shastri
I. Rousochatzakis
Pavia Univ. Italy
Dr. A. Lascialfari
E. Micotti
Korea
Prof. D.-Y. Jung
Y. J. Kim

3. Spin Dynamics in AF Rings or Clusters
A strong enhancement
at kBT  J
Universal Behavior ?

4. Universal Scaling Behavior

5. Polyoxovanadate Compounds

6. Spin Hamiltonian and Susceptibility
Heisenberg Spin Square: {V12} J J J J
|2,1,1>
|0,0,0>,|1,0,1>,|1,1,0>
|1,1,1>
|0,1,1> Ho

7. Magnetization measurement of {V12}

8. 1/T1 of V12

9. 1/T1 of {V12} At low T: 1/T1  exp(-(H)/kBT) (H) = 0 –gBH 0 = |J|
Procissi et al., to be submitted

10. T-Behavior of 1/T1 in Polyoxovanadates
In V6, V12: 1/T1 is similar to T.
The absence of an enhancement of
1/T1 for kBT  J
In V15: The presence of broad peak of 1/T1:
similar to the critical enhancement in other
AF clusters with s > 1/2
? spin triangle of five s = ½ spins
- In 1/T1 of V12: The peak at T  19 K (cf J = K)
appears to be associated with the critical
slowing down of magnetic fluctuations.
(very weak enhancement)
- At low temperatures: 1/T1  exp(-(H)/kBT)

11. V6 [2 x V3] Mn3 [Mn(II) + 2Mn(III)] M. Luban, PRB 66, 054407 (2002)
Mn3: Mgnetic Susceptibility
V6 [2 x V3]
 M. Luban, PRB 66, (2002)
S1 = S2 = S3 = 1/2
g = 1.95
J = K, J’ = -6.9 K,
 = J’ – J = 57.7 K V6
Mn3 [Mn(II) + 2Mn(III)]
[Mn3O(O2CCH3)6(C5H5N)3]C5H5N
S1 = 5/2, S2 = S3 = 2
g = 2.10
J = -7.9 K, J’ = K
 = -3J/2  12 K

12. Average distance of H from Mn3O: <r>  3 Å
1H NMR Linewidth in Mn3
(4.2 K) = 7.7 x cm3/Mn
(295 K) = 0.29 x10-26
Az (4.2 K) = 3.9 x 1022 cm-3
Az (295 K) = 3.5 x 1022 cm-3
Average distance of H from
Mn3O:
<r>  3 Å

13. Distinct behavior of NMR relaxation 1/T1: ascribed to the different
1H Spin-Lattice Relaxation Rate vs. Temperature in Mn3
Distinct behavior of NMR
relaxation 1/T1:
ascribed to the different
spin values ??
V6: S1 = S2 = S3 = 1/2
(Quantum Spins ?)
Mn3: S1 = 5/2, S2 = S3 = 2
(Classical Limit ?)

14. Strong Enhancement of 1/T1: Slowing down of magnetic fluctuations
Spin Dynamics in Mn3
Strong Enhancement of 1/T1:
Slowing down of magnetic
fluctuations
 Building up of AF
correlation
Low Temperature Side:
1/T1  exp(-U/T)
U = NMR : Effective Gap
U = 19 K at H = 1.5 T
U = 15 K at H = 7.2 T

15. Spin Dynamics in AF Clusters
T dependence is well understood.
Critical enhancement and its universal scaling behavior:
to be published soon by F. Borsa and M. Luban et al.,
Absence of critical enhancement or weak critical
enhancement in s = ½ systems ???
At low temperatures:
1/T1  exp(-(H)/kBT)
good for Stotal = 0
but for Stotal  0 ???

16. Magnetization Measurements of Mn12 Clusters and
Artificially Engineered Ferritins
Prof. S. Yoon, M. Heu, S. W. Yoon, S.-B. Cho, B. J. Kim
(The Catholic Univ. of Korea)
Prof. Z. H. Jang
(Kookmin Univ. Korea)
Prof. D.-Y. Jung, Y. J. Kim
(SKKU Univ. Korea)
Prof. K. S. Kim
(Jeonbuk National Univ. Korea)

17. Mn12-Ac : [Mn12O12(O2CCH3)16(H2O)4]·2CH3CO2H·4H2O
Mn12-PrCl : [Mn12O12(O2CCH2CH2Cl)16(H2O)4]·CH2ClCH2CO2H
Mn12-BuCl : [Mn12O12(O2CCH2CH2Cl)16(H2O)4]·2CH3ClC6H5
M12-Ac Mn12-PrCl Mn12-BuCl
tetragonal triclinic triclinic
a = Å Å Å
b = Å Å Å
c = Å Å Å
13.72Å ~20.30Å
distance between Mn12 clusters

18. 2mm
Mn12-Ac

19. 1mm
Mn12-PrCl
D/g=0.30K

20. Mn12-BuCl

21. Relaxation at H=0
Mn12-BuCl
Mn12-PrCl

22. Relaxation Time and Activation Energy

23. Relaxation in PrCl is faster at on-resonance fields

24. Triclinic : S=10, D=0.56K, g=1.90, E=0.15K
Mn12-PrCl
Triclinic : S=10, D=0.56K, g=1.90, E=0.15K

25. After being measured, sample 1 was heated
2mm
Heat Treatment
After being measured, sample 1 was heated
up to 50 oC (1 oC/min) and quenched

26. Thermogravimetric Analysis (TGA)
[Mn12O12(O2CCH3)16(H2O)4]·2CH3CO2H·4H2O
Mn12-Ac
MnO+MnO2

27. Uniaxial symmetry is not changed
S=10, D=0.67K, g=1.97
Uniaxial symmetry is not changed

28. Mn12-Ac
S0: as prepared
S1: after heat treatment

29. QTM in Mn12 Clusters Strongly related to bulk and/or local structure
Local structure means:
? Local distortion
? Dislocation
? Jahn-Teller Isomerisom

30. Ferritin
- Two types of protein chains:
H-Chain
L-Chain

31. Recombinant human ferritin homopolymers were
successfully produced in E Coli transformed with
human ferritin H or L-chain genes, respectively. 
Apoferritins were then reconstituted with Fe
atoms under the variable experimental conditions. 
HF (reconstituted ferritin with H-chain only):
900 Fe/molecule
LF (reconstituted ferritin with L-chain only):
800 Fe/molecule
- Molecular based device: V I

32. Blocking Temperarture, TB

33. M vs H
Mo(T)=M*(TN-T)/TN
Big Difference in eff
Modified Langevin Function:
M = MoL(effH/kBT) + H

34. T-behavior of the linear susceptibility 

35. Ferritin ? The unusual behavior of TB(H) with a broad peak:
Distribution of the energy barrier
which depends on the applied field
? However, the distribution is not simply due to
size distribution.
? eff(L) > eff(H) even for the similar size:
- not only from the uncompensated spins on the surface
- but also from a kind of random defects
and the number of defects can be distributed even
for the same size of molecules
? The strong T-dependence of linear susceptibility 