1. Nagoya Univ. Kunio Awaga
Quantum Spin Systems
in Molecule-based Magnetic Materials
Nagoya Univ. Kunio Awaga
Molecule-based magnetic materials
2. Chemical modifications of Mn12 and their influences
( 3. Unusual physical properties of thiazyl radicals )

2. Characters of molecule-based magnetic materials
a. Spin polarization
McConnell’s Proposals for
Ferromagnetic Intermolecular Interactions
S=1/2
Type I: H = -JSASB = -SASB S Jij riA rjB
Type II: Resonance with S=1 CT State
Negative spin density M X
Organic Ferromagnetism

3. 1D b. Strong spin-lattice interactions
Dia-Paramagnetic Phase Transition 1D
Spin-Peierls Transition
antiferromagnetic
ferromagnetic
Galvinoxyl
K. Mukai, H. Nishiguchi, Y. Deguchi, J. Phys. Soc. Jpn., 23, (1967).
K. Awaga, T. Sugano and M. Kinoshita, J. Chem. Phys., 85, 2211 (1986).

4. Pressure-induced ferro- to antiferro-magnetic transition
c. Controllable properties
Photomagnets
S=0
S=0
S=3/2
S=1/2
Red light
Blue light
Nonmagnetic
Ferrimagnet
Mito, Masaki; Kawae, Tatsuya; Takumi, Masaharu; Nagata, Kiyofumi; Tamura, Masafumi; Kinoshita, Minoru; Takeda, Kazuyoshi. Phys. Rev. B: Condens. Matter (1997), 56(22), R14255-R14258.
O. Sato, T. Iyoda, A. Fujishima, K. Hashimoto,
Science, 272, 704 (1996)

5. d. Good models Heisenberg spins Low-dimensional spin systems
Organic Kagome Antiferromagnet
Intradimer: J1 ~10 K
S=1
Interdimer: J2 ~ -1 K
K. Awaga, T. Okuno, A. Yamaguchi, M. Hasegawa, T. Inabe, Y. Maruyama and N. Wada, Phys. Rev. B, 49, 3975 (1994).
Spin Frustration !

6. Spin Gap ! Gapless ! S=1 Spin Frustration on Kagome Lattice S=0
N. Wada, T. Kobayashi, H. Yano, T. Okuno, A. Yamaguchi and K. Awaga,
J. Phys. Soc. Japan, 66, 961 (1997).

8. Single molecule magnets
e. Spin clusters
Single molecule magnets
[MnIVMnIII3O3Cl4(O2CCH3)3(py)3]
[MnIV2MnIII2(pdmH)6(O2CCH3)2(H2O)4](ClO4)2
[FeIII4(OCH3)6(dpm)6]
[VIII4O2(O2CC2H5)7(bipy)2](ClO4)
[Mn4IIMn3III(teaH)3(tea)3](ClO4)2•3CH3OH
[Cr{(CN)Ni(tetren)}6](ClO4)9
{[FeIII8O2(OH)12(tacn)6]Br7•H2O}[Br•8H2O]
[FeIII10Na2O6(OH)4(O2CC6H5)10(chp)6(H2O)2{(CH3)2CO}2]
[MnIV4MnIII8O12(O2CCH3)16(H2O)4]•2CH3CO2H•4H2O (Mn12)
{[Fe17O4(OH)16{N(CH2CO2H)2(CH2CH2OH)}8(H2O)12]+
　　[Fe19O6(OH)14(N(CH2CO2H)2(CH2CH2OH))10(H2O)12]+}
Co24(OH)18(OCH3)2Cl6(2-methyl-6-hydroxypyridine)22
[MnIVMnIV26MnII3O24(OH)8(O2CCH2C(CH3)3)32(H2O)2(CH3NO2)4]

9. 2. Chemical modifications of Mn12 and their influences
a. Chemistry of Mn12
b. Jahn-Teller isomerisom in Mn12
c. Quantum Effects in Mn11Cr
（Hokkaido univ.）K. Takeda, T. Inabe
（Tokyo univ.）　A. Yamaguchi, H. Ishimoto, T. Tomita, H. Mitamura,
T. Goto, N. Mouri
（Okayama Sci. univ.) H. Nojiri
（Kyoto univ.) T. Goto
（Nara Univ. Educ.）T. Kubo
（Nagoya univ.）　Y. Suziki、H. Hachisuka
（Inst. Mol. Sci.) 　T. Yokoyama

10. a. Chemistry of Mn12 Synthsis of Mn12 MnII(CH3COO)2 ＋ KMnVIIO4
[Mn12III, IVO12(CH3COO)16(H2O)4]
60% CH3COOH
(Mn12Ac)
T．Lis, Acta Cryst., B36, 2042 (1980).

11. Core structure of Mn12 I II II Mn3+ Mn４+ Site I I O2- Site II II I
Mn(III) sites
JT軸

12. Ligand exchange Mn12Ac Mn12Ph Mn12Ph・2PhCOOH R=CHCl2 ax
R. Sessoli et al., J. Am. Chem. Soc., 155, 1804 (1993).
excess C6H5COOH
hexane
Mn12Ac
Mn12Ph
CH2Cl2
layering
excess C6H5COOH
excess C6H5COOH
Mn12Ph・2PhCOOH
CH2Cl2
evaporation
CH2Cl2
K Takeda, K. Awaga and T. Inabe, Phys. Rev. B, 57,11062 (1998).
M. Soler, et al. Inorg. Chem., 40, 4902 (2001).
Mixed-Carboxylate Complexes [Mn12O12(O2CR)8(O2CR')8(H2O)4]
R=CHCl2 ax
Basicities: ButCH2CO2- >> CHCl2CO2-
R’=CH2But eq

13. Mn-Fe mixed cluster Mn12Ac Fe(CH3COO)2 ＋ KMnO4
A. R. Schake et al., Inorg. Chem., 33, 6020 (1994).
55  ºC
Fe(CH3COO)2 ＋ KMnO4
[Fe4Mn8O12(CH3COO)16(H2O)4]
60 % CH3COOH
Fe3+
(site II)
Mn12Ac
MnII(CH3COO)2
KMnVIIO4
MnIII (site II)
MnIII (site I)
MnIV
Ground state is S=0 !?

14. b. Jahn-Teller isomerisom in Mn12
K. Takeda and K. Awaga, Phys. Rev. B, 56, (1997).
K Takeda, K. Awaga and T. Inabe, Phys. Rev. B, 57,11062 (1998).
K. Takeda, K. Awaga, T. Inabe, A. Yamaguchi, H. Ishimoto, T. Tomita, H. Mitamura, T. Goto. N. Mori, H. Nojiri, Phys. Rev. B, 65, (2002).

15. Magnetic properties of Mn12
1) High spin
S = 9~10
2) Uniaxial Magnetic Anisotropy
D = -0.6 K
Mn(III) (S=2)
Mn (IV) (S=3/2)
Impurity!?
H. J. Eppley et al.,
J. Am. Chem. Soc.,
117, 301 (1995).

16. A+ [Mn12Ph]- PPh4+ m-MPYNN+ 1.7 K x1/6 (m-MPYNN+) [Mn12Ph]-
K. Takeda and K. Awaga, Phys. Rev. B, 56, (1997).

17. Solvated Mn12 (Batch A) Single Crystal includes both SR and FR !!
Mn12Ph・2PhCOOH
K Takeda, K. Awaga and T. Inabe, Phys. Rev. B, 57,11062 (1998). K. Takeda, K. Awaga, T. Inabe, A. Yamaguchi, H. Ishimoto, T. Tomita, H. Mitamura, T. Goto. N. Mori, H. Nojiri, Phys. Rev. B65, (2002).
t = 100s TB
T= temp. of max. in c” D
D=|D|Sz2
(Batch A)
Single Crystal includes both SR and FR !!
TB=1.3 K
2.7 K

18. SR : FR = 1 : 2
(Batch A)

19. TB=2.7 K
TB=1.3 K

20. Batch B
Only includes FR molecules

21. Crystal Structure（Batch B）
170 K a
Crystal Solven
Molecular Axis
49゜
Mn12
49゜ b O

22. Molecular Structure of FR Molecule（Batch B）
top view
Elongated Octahedron
Mn3~Mn6*
Mn7
Compressed Octahedron

23. Chemical Pressure side view Ligand between Mn6 and Mn7
Crystal Solvent Molecule

24. Magnetic Anisotropy of FR Molecules
Tilted by 12° b a b
Magnetic Easy axis
90°=a
60°
30°
１２°
４９°
0°=b
Molecular Axis a
10 K
DFR/kB= K
g= 1.9
S=10

25. High-field EPR（428.9 GHz）for FR in ab plane
-30°
50° b
Easy axis
4１°
0°=b
Hard plane
Mol. axis S2
30°
Max. of
Res. Field
Mol. axis
60° S1 a
90°=a
by H. Nojiri

26. Angular dependence of the resonance field
in the hard plane for FR species
・Strong Uniaxial anisotropy
0°= c axis
・Anisotropy even in the hard plane
・Two kinds of FR
30°
60°
90°= ab plane
120°
150°
DFR/kB= K
g= 1.9
EFR/kB= K
S=10

27. Magnetic Anisotropy of SR Molecules
Magnetic Easy Axis
of SR Molecules
Agrees with
Molecular Axis
QTM for SR Molecules
q=90 (a axis)
q=60
q=30
q=0 (b axis)

28. QTM for FR
Magnetization curve for Batch B at 0.7 K in the field parallel to the b axis.
0.7 K
D/kB=-0.27 K

29. High pressure effects on Mn12Ac
Y. Suzuki, K. Takeda and K. Awaga
Single Crystal in Be-Cu cell
SQUID

30. Sweep rate dependence of magnetization curves
0 GPa
0.6 GPa
Little dependence at the zero field !

31. Sweep-rate dependence of tunneling probability PN1 2 3
N=0

32. Pressure depend. of FR:SR
Sigmoid function:
MFR = 2MsFR/[1 + exp(-H/A)] + B
Pressure depend. of FR:SR

33. Summary (1) SR Molecule FR Molecule JT ion, Mn3+ Mn7 (site II)
Chemical
Pressure
JT ion, Mn3+
Mn7
(site II)
TB=2.7 K
TB=1.3 K
Uniaxial Anisotropy
Biaxial Anisotropy

34. (2) [Mn12Ph]- (3) Exchange and Tunneling Effects ??? SR FR
m-MPYNN+
[Mn12Ph]-
Exchange and Tunneling Effects ???
(3) SR FR
Step at zero field is mainly caused by FR

36. Magnetic anisotropy barrier for spin tunneling in Mn12O12 molecules Pederson MR, Khanna SN PHYSICAL REVIEW B 60, pp (1999).
CHEM. PHYS. LETT. 307, pp (1999) .
Fourth-order magnetic anisotropy and tunnel splittings in Mn-12 from spin-orbit-vibron interactions Pederson MR, Bernstein N, Kortus J PHYSICAL REVIEW LETTERS 89, no (2002).
Magnetic ordering, electronic structure, and magnetic anisotropy energy in the high-spin Mn-10 single molecule magnet Kortus J, Baruah T, Bernstein N, Pederson MR PHYSICAL REVIEW B 66, no (2002).

37. Magnetic bistability and photo-induced phase transition in TTTA
2. Unusual physical properties of thiazyl radicals
Magnetic bistability and photo-induced phase transition in TTTA
W. Fujita and K. Awaga, Science, 286, pp (1999).
W. Fujita, K. Awaga, H. Matsuzaki, H. Okamoto, Phys. Rev. B65, (2002).

38. RT Magnetic Bistability
Diamagnetic-Paramagnetic Phase Transition in TTTA
Room Temp.
100 K
RT Magnetic Bistability

39. Intradimer arrangement
Crystal Structures of TTTA
Regular
SOMO
Dimerized
Intradimer arrangement

40. Polarized Reflection Spectra of TTTA
U~2 eV
at RT LE CT
By H. Matsuzaki, H. Okamoto (Univ. of Tokyo)

41. Polarized Reflection Spectra Polarized Microscope Images
(Ei // stacking axis) HT
stacking
axis LT
50m
by H. Matsuzaki, and H. Okamoto
(Tokyo Univ.)

42. Polarized Microscope Images (Ei // stacking axis)
Irradiated Area
LT phase
Before
296K
After
Eexc // stacking axis h=2.64 eV (470 nm)
6 ns pulse 1shot
1) No transition with CW laser.
2) Ith in excitation photon density.
3) No transition from HT to LT.
Photo-Induced Phase Transition !

43. Conductivities of TTTA
Room temp.
HT phase: s ～10-8 W-1cm-1
Mott Inslator
LT phase: s ～10-9 W-1cm-1
By T. Inabe (Hokkaido Univ.)

44. Acknowledgement
（Hokkaido univ.）K. Takeda, T. Inabe
（Tokyo univ.）　A. Yamaguchi, H. Ishimoto, T. Tomita, H. Mitamura,
T. Goto, N. Mouri
（Okayama Sci. univ.) H. Nojiri
（Kyoto univ.) T. Goto
（Nara Univ. Educ.）T. Kubo
（Nagoya univ.）　Y. Suziki、H. Hachisuka
（Inst. Mol. Sci.) 　T. Yokoyama