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

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

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

Universal Scaling Behavior

Polyoxovanadate Compounds

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

Magnetization measurement of {V12}

1/T1 of V12

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

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 = -17.6 K) appears to be associated with the critical slowing down of magnetic fluctuations. (very weak enhancement) - At low temperatures: 1/T1  exp(-(H)/kBT)

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, 054407 (2002) S1 = S2 = S3 = 1/2 g = 1.95 J = -64.6 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’ = -27.6 K  = -3J/2  12 K

Average distance of H from Mn3O: <r>  3 Å   1H NMR Linewidth in Mn3   (4.2 K) = 7.7 x10-26 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  

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 ?)  

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  

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 ???

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)

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 = 17.319Å 16.355Å 14.556Å b = 17.319Å 17.635Å 14.582Å c = 12.388Å 19.243Å 27.265Å 13.72Å 12.92~20.30Å distance between Mn12 clusters

2mm Mn12-Ac

1mm Mn12-PrCl D/g=0.30K

Mn12-BuCl

Relaxation at H=0 Mn12-BuCl Mn12-PrCl

Relaxation Time and Activation Energy

Relaxation in PrCl is faster at on-resonance fields

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

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

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

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

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

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

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

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

Blocking Temperarture, TB

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

T-behavior of the linear susceptibility 

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 