Nagoya Univ. Kunio Awaga
1. Molecule-based magnetic materials
2. Chemical modifications of Mn12 and their influences
( 3. Unusual physical properties of thiazyl radicals )
Characters of molecule-based magnetic materials
a. Spin polarization
S=1/2
H
McConnell’s Proposals for
Ferromagnetic Intermolecular Interactions
Type I: H = -JSASB = -SASB S Jij riA rjB
H
H
Type II: Resonance with S=1 CT State
H
H
H
Negative spin density
H
M
H
H
H
H
M
H
H
X
H
H
Organic Ferromagnetism
b. Strong spin-lattice interactions
S=1/2
Dia-Paramagnetic Phase Transition
Spin-Peierls Transition
antiferromagnetic
Galvinoxyl
K. Mukai, H. Nishiguchi, Y.
Deguchi, J. Phys. Soc. Jpn.,
23, 125 (1967).
K. Awaga, T. Sugano and M.
Kinoshita, J. Chem. Phys.,
85, 2211 (1986).
(H3C)3C
C(CH3)3
O
O
C(CH3)3
C(CH3)3
1D
ferromagnetic
Pressure-induced ferro- to
antiferro-magnetic transition
c. Controllable properties
O
Photomagnets
N
C
N
A
N
C
B
N C
C
N
C
N
B
C N
C
C
N
B
C NC N
A
N C C
C
N
N
C
A
N
C
C
N
A
AN
C
BC
B
N C
N
B
C
A
C N
C
C
N
S=0
S=0
Co3+ C
N
N
B
C
BC
C
N CN C
C
A
N
AN
A
C
N
N
C N
N
B
N
C
C
N C
N C
A
B
C
N
O
A
N
C
N
N
N
C N
C
C
C
N
N
C N
NO2
B
N
B
N
C
N
C
B
C
C
N
N C
N
N
N
N
C
C
N
A
N
C
C
C N
N
A
C
N
N
C
Red light
B
S=3/2
S=1/2
Co2+ C
Fe2+
Blue light
Nonmagnetic
O. Sato, T. Iyoda, A. Fujishima, K. Hashimoto,
Science, 272, 704 (1996)
N
Fe3+
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.
d. Good models
O=
Heisenberg spins
Low-dimensional spin systems
N+
CH3
N+
X- (= I -, BF4 -, ClO4 -, .. . )
N
O
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 !
O
N
N
+
CH3
N
BF4 -
Spin Frustration
on Kagome
Lattice
O
Spin Gap !
S=1
S=0
Gapless !
N. Wada, T. Kobayashi, H. Yano, T. Okuno, A. Yamaguchi and K. Awaga,
J. Phys. Soc. Japan, 66, 961 (1997).
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]
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
a. Chemistry of Mn12
Synthsis of Mn12
MnII(CH3COO)2 ＋ KMnVIIO4
55 ºC
60% CH3COOH
T．Lis, Acta Cryst., B36, 2042 (1980).
温度
55 ℃
15 ℃
0
3
9 hrs
時間
[Mn12III, IVO12(CH3COO)16(H2O)4]
(Mn12Ac)
I
Core structure of
Mn12
II
II
Mn3+
Site I
Mn４+
I
O2-
Site II
I
Site I
Mn(III) sites
JT軸
II
Site II
R. Sessoli et al., J. Am. Chem. Soc., 155, 1804 (1993).
Ligand exchange
Mn12Ac
excess C6H5COOH
hexane
CH2Cl2
layering
excess C6H5COOH
CH2Cl2
Mn12Ph
excess C6H5COOH
evaporation
Mn12Ph・2PhCOOH
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
R’=CH2But
eq
Basicities: ButCH2CO2- >> CHCl2CO2-
Mn-Fe mixed cluster
A. R. Schake et al., Inorg. Chem., 33, 6020 (1994).
55 ºC
Fe(CH3COO)2 ＋ KMnO4
60 % CH3COOH
[Fe4Mn8O12(CH3COO)16(H2O)4]
Fe3+ (site II)
Mn12Ac
MnII(CH3COO)2
MnIII (site II)
Ground state is S=0 !?
KMnVIIO4
MnIII (site I)
MnIV
b. Jahn-Teller isomerisom in Mn12
K. Takeda and K. Awaga, Phys. Rev. B, 56, 14560 (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, 094424 (2002).
1) High spin
Magnetic properties of Mn12
S = 9~10
2) Uniaxial Magnetic Anisotropy
D = -0.6 K
ms=0
12
3
4
5
6
Mn(III) (S=2)
Mn (IV) (S=3/2)
-2 -1
-3
-4
-5
-6
7
-7
DSz2
8
9
10
~ 50 K
-8
-9
-10
Impurity!?
H. J. Eppley et al.,
J. Am. Chem. Soc.,
117, 301 (1995).
A+ [Mn12Ph]O+
N
N
PPh4+
O
CH3
+
N
m-MPYNN+
1.7 K
x1/6
(m-MPYNN+) [Mn12Ph]-
K. Takeda and K. Awaga, Phys. Rev. B, 56, 14560 (1997).
Solvated Mn12
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, 094424 (2002).

=|D|Sz2
(Batch A)
t
1
2 ac
  

k
T
 B 
t  t 0 exp 
T= temp. of max. in c”
t = 100s
TB
TB=1.3 K
2.7 K
Single Crystal includes both SR and FR !!
M
MS
H0
O
SR : FR = 1 : 2
MLSR
MLFR
(Batch A)
1  exp  2 A(H  H0 )
1  exp  2 A(H  H0 )

MSSR

FR 1  exp
MS
MT  CH
H
 2B(H  H0 )
1  exp  2B(H  H0 )
TB=2.7 K
TB=1.3 K
Batch B
Only includes FR molecules
Crystal Structure（Batch B）
170 K
a
Crystal Solven
Molecular Axis
49゜
Mn12
49゜
O
b
Molecular Structure of FR Molecule（Batch B）
top view
C2
Elongated Octahedron
Mn3
Mn4
Mn3~Mn6*
Mn5
Mn7
Mn6
Mn7
Compressed Octahedron
C2
Chemical Pressure
side view
Ligand between Mn6 and Mn7
Mn7
Crystal Solvent Molecule
c axis
Magnetic Anisotropy of FR Molecules
b
a
Tilted by
12°
b
Magnetic Easy axis
90°=a
60
°
30
°
0°=b
４９°
１２°
Molecular Axis
a
10 K
DFR/kB= -0.45 K
g= 1.9
S=10
High-field EPR（428.9 GHz）for FR
in ab plane
-30°
50°
b
0°=b
Easy axis
4１°
Hard plane
Mol. axis
S2
30°
Max. of
Res. Field
Mol. axis
60°
S1
a
90°=a
by H. Nojiri
Angular dependence of the resonance field
in the hard plane for FR species
0°= c axis
・Strong Uniaxial anisotropy
・Anisotropy even in the hard plane
・Two kinds of FR
30°
60°
90°= ab plane
120°
150°
DFR/kB= -0.55 K
EFR/kB= -0.09 K
g= 1.9
S=10
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)
3
QTM for FR
(a)
M (arb. units)
2
Magnetization curve for
Batch B at 0.7 K in the
field parallel to the b axis.
1
0
-1
-2
0.7 K
dM/dH (arb. units)
-3
0.20
(b)
0.15
0.10
0.05
D/kB=-0.27 K
0.00
-3
-2
-1
0
H (T)
1
2
3
High pressure effects on Mn12Ac
Y. Suzuki, K. Takeda and K. Awaga
Single Crystal in Be-Cu cell
SQUID
Sweep rate dependence of magnetization curves
0 GPa
0.6 GPa
Little dependence at the zero field !
Sweep-rate dependence
of tunneling probability PN
N=0
N=
0 1 2 3
Pressure depend. of FR:SR
Sigmoid function:
MFR = 2MsFR/[1 + exp(-H/A)] + B
Summary
(1)
SR Molecule
FR Molecule
"
"
Chemical
Pressure
JT ion, Mn3+
Mn7
(site II)
TB=2.7 K
Uniaxial Anisotropy
TB=1.3 K
Biaxial Anisotropy
(2)
ON+
CH3
+
N
N
[Mn12Ph]-
Exchange and Tunneling Effects ???
O
m-MPYNN+
(3)
SR
FR
Step at zero field is mainly caused by FR
CHEM. PHYS. LETT. 307, pp. 253-258 (1999) .
Magnetic anisotropy barrier for spin
tunneling in Mn12O12 molecules
Pederson MR, Khanna SN
PHYSICAL REVIEW B 60, pp. 95669572 (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. 097202 (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. 092403 (2002).
2. Unusual physical properties of thiazyl radicals
Magnetic bistability and photo-induced phase transition in
TTTA
N
S
N
S
N
S
W. Fujita and K. Awaga, Science, 286, pp. 261-262 (1999).
W. Fujita, K. Awaga, H. Matsuzaki, H. Okamoto, Phys. Rev. B65, 064434 (2002).
Diamagnetic-Paramagnetic Phase Transition in
TTTA
Room Temp.
100 K
RT Magnetic Bistability
:C
Crystal
Structures
of TTTA
HT phase
:N
:S
a
b
b
S
N
c
N
S
S
N
Regular
c
SOMO
a
O
LT phase
c
N
S
N
N
S
N
S
N
b
S
S
N
S
Intradimer arrangement
a
b
Dimerized
c
O
O a
Polarized Reflection Spectra of TTTA
U~2 eV
at RT
LE
CT
By H. Matsuzaki, H. Okamoto (Univ. of Tokyo)
Polarized Reflection Spectra
Polarized Microscope Images
(Ei // stacking axis)
0.3
Ei // stacking axis
296K
LT
0.2
HT
HT
R
0.1
0
stacking
axis
1
2
3
Photon energy (eV)
4
LT
50m
by H. Matsuzaki, and H. Okamoto
(Tokyo Univ.)
Polarized Microscope Images (Ei // stacking axis)
Irradiated Area
LT phase
Before
296K
Eexc // stacking axis h=2.64
After
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 !
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.)
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