A Novel System of Single-Chain Quantum Magnet: Twisted XY Easy-Plane Anisotropy Model and Photo-Induced Switching between Quantum Magnet and Paramagnet

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A Novel System of Single-Chain Quantum Magnet
Twisted XY Easy-Plane Anisotropy Model and
Photo-Induced Switching between Quantum Magnet
and Paramagnet
Masahiro Yamashita, Takashi Kajiwara, Yukihiro
Kaneko, Motohiro Nakano, Shinya Takaishi, Tasuku
Ito, Hiroyuki Nojiri, Norimichi Kojima, and
Masaki Mito (Tohoku University CREST(JST),
Osaka University, The University of Tokyo, and
Kyushu Int. of Thechnology)
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Organic-Inorganic Hybrid system
Nano-Science of Advanced Metal Complexes
Non-Linearity Quantum Effect
Nano-Size Nano-Space
Bottom-Up Self Assembly
3
Single Molecule Quantum Magnets, SMMs
Multinuclear nanocluster metal complexes
A single molecule behaves like a magnet
Quantum tunneling effect
Frequency dependent ac susceptibility
Cole-Cole plot Heat Capacity Linear
Arrhenius plots
Uni-axis anisotropy Isolated molecules
4
Quantum Dots Single Molecule Magnets
Mn12O12(O2CR)16(H2O)4 S 10
Quantum spin tunneling
ms 0
D/kB DS2
D/kB
Hendrickson, D. N. Christou, G. et al, J. Am.
Chem. Soc., 1988, 110, 8537. Gatteschi, D. et al,
Science, 1994, 265, 1054.
ms 10
ms -10
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Magnets
Bulk Magnets
Quantum Magnets
Increase of the capacity
Development of the property
_at_ Clusters Nano-Dots S 3, 9, 10. Anisotropy 6.0
2 x 1023 bit/mol
_at_ Ising 1-D Chains Nano-Wires Tuning of S and
J Large Anisotropy
2-D and 3-D Networks 8 x 109 bit (1GB)
Molecular memory Quantum computing device
6
Reported Single Chain Magnets
D. Gatteschi et al., 2001
H. Miyasaka et al., 2002
T. -F. Liu et al., 2003
M. Verdaguer et al., 2003
M. Ferbinteanu et al., 2005
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Twisted XY system A Novel SCM
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catena-FeII(ClO4)2FeIII(bpca)2ClO43MeNO2
Reaction of FeII(bpca)2 and FeIII(H2O)6(ClO4)3
gave dark red crystals of alternate chain
complex, catena-FeII(ClO4)2FeIII(bpca)2ClO4.
Monoclinic, P21/n, a 13.719(3) Å, b
18.428(4) Å, c 15.355(4) Å, ß 90.189(5),
U 3882.1(15) Å3, T 240 K, R1 0.0690
Fe(II) (h. s.)
Fe(III) (l. s.)
FeII-FeIII distance 5.178 Å
FeII
FeIII
FeII
FeIII
FeII
FeIII
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Low spin Fe(III) ion in an axially shortened
octahedron.
2.136(2)
elongated
1.975(2)
1.896(2)
2.047(2)
compressed
High spin Fe(II) ion in an axially elongated
octahedron. Coordination of the carbonyl oxygen
atoms in an equtorial plane and elongated
octahedral geometry would result into a
zero-field splitting parameter D gt0, a hard-axis
type anisotropy along the perchlorate
coordination axis, or, easy plane type anisotropy
in the equatorial plane.
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Interchain FeFe distances FeIIFeIII 10.17
Å FeIIFeII 10.28 Å FeIIIFeIII 10.33 Å
Chains are magnetically separated.
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magnetic field
Twisted easy-plane systemA Novel SCM. A new
Ising system with positive D.
cf. AF Ising system D MUST be negative.
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Magnetic behavior in dc field of a single crystal
M / a.u.
µeff / µB
T / K
H / kOe
Left The magnetization vs. filed. Right meff
vs. temp. for a single crystal. Magnetic
measurements on an oriented single crystal of the
chain complex in the dc field applied along the
chain (D)and perpendicular to the chain (x).
Hpara
Hperp
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Magnetic behavior in dc field of microcrystals
Ferrimagnetic behavior
J
J
J
J
J
J
J
FeII FeIII FeII FeIII
FeII FeIII
S 2
S 1/2
Spin only value for S 2 and S 1/2 system is
5.2 µB with g 2. At 3 K, 1213
Fe(III)-Fe(II) units are magnetically aligned.
µeff / µB
T / K
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x
2J
z
y
The following Hamiltonian was used to
analyze Sj is either an S 2 spin
from FeII for even values of j or an S 1/2
spin from FeIII for odd values of j J is the
superexchange interaction between neighboring
FeII and FeIII ions D is the uniaxial zero-field
splitting parameter for FeII spins. J/kB and
D/kB were estimated to be 10.0 K and 14.9 K.
Positive D was directry confirmed by HF-EPR
spectrum.
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Magnetic behavior of microcrystals in ac field
3 Oe ac field and 0 dc field. Upon cooling,
cm increased to reach the max. values at around
3.252.25 K, and when the cm signals became
smaller, cm signals appeared. The cm peak
shifted from 2.9 to 1.9 K dependeng on the
frequency.
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Cole-Cole diagram
Plot of cm' vs. cm" (Cole-Cole plot) at various
temperatures. The solid lines represent the
least-square fits obtained with a Debye
model. At fixed temperatures of 2.03.4 K,
semicircle Cole-Cole diagrams with a 0.090.13
were obtained, which indicates that relaxation
via single processes
cm / emu mol1
cm' / emu mol1
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Mossbauer spectra
298 K
Typical paramangetic spectra of
Fe(II)(HS)Fe(III)(LS) system. IS 1.15 and QS
2.49 mm s-1 for high-spin Fe(II)
IS 0.03 and QS 0.41 mm s-1 for
low-spin Fe(III) Magnetically Ordered specta.
Below 7 K, a slow paramagnetic relaxation
broadening ocurred, and at 3.7 K, two sets of
sextet signals appeared
200 K
77 K
40 K
Transmission /
20 K
7 K
3.7 K
Velocity / mm s-1
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Arrhenius plot
Mossbauer Time-scale
t t 0 exp(D/kBT)
ln(2pn)
D/kB 27(1) K t0 1.6(6) x 108 s
t0(1.3K) 100 s (blocking
temperature)
T-1 / K-1
From an ln(2pn) vs. 1/T plot, t0 and D/kB were
estimated to be 1.6(6) x 108 s and 27(1) K,
respectively. Using these values, the blocking
temperature (t(T) 100 s) was calculated as 1.3
K.
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Optical property
e-
I
II
III
MIII FeIII
I II
solid
solution
KBr
II
Fe(II)/Fe(III) in II E1/2 0.35 V (vs.
SSCE) Both Fe(II) and Fe(III) are stabel
solv. MeNO2
I
e / 103 M-1 cm-1
Abs.
l / nm
l / nm
CT interaction occurs
solution
solid
III
KBr
I II
II
solv. MeNO2
II
I
I
e / 103 M-1 cm-1
Abs.
Co(II)/Co(III) in II E1/2 -0.28 V (vs. SSCE)
l / nm
l / nm
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Magnetic Properties under Irradiation
No irradiation (0)
1/8
0
1/4
light intensity
1/2
cmT / emu K mol-1
1
strong
T / K
light source He-Ne laser wave length 612nm 5mW
Neutral density filters (1/2, 1/4) were used to
regulate light intensity
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?mT / emu K mol-1
T/K
cm / emu mol-1
cm / emu mol-1
T / K
T / K
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cmT / emu K mol-1
T/K
cm / emu mol-1
cm / emu mol-1
T/K
T/K
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Magnetic Properties under Irradiation
f 1000Hz
f 1000Hz
cm / emu mol-1
cm / emu mol-1
T / K
T / K
1/8
1/4
1/2
1
strong
0
Blocking Temp. lowered when the light intensity
increased.
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Magnetic Properties under Irradiation
T 2.4K
Arrhenius plot
Cole-cole plot
cm / emu mol-1
-lnt
cm / emu mol-1
T-1 / K-1
Irrad. 0 1/8 1/4 1/5 1
D / kB 23(1) 19(1) --- --- ---
a 0.17 0.19 0.18 0.17 ---
Energy barrier is decreassed under irradiation
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Mechanism
S 4/2
S 1/2
l.s. Fe(III)
h.s. Fe(II)
l.s. Fe(III)
h.s. Fe(II)
Paramagnetic l.s. Fe(III) turuns to diamagnetic
l.s. Fe(II) by MMCT
Diamagnetic l.s. Fe(II) (S 0) divides the
chain in the view of magnetism, and then the
energy barrior decreses. The unit number can be
controled by light intensity.
? / kB
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Switching of Magnetism by Irradiation
Absorption spectrum of Fe(III)-Fe(II)-Fe(III)
moiety
e / M1 cm1
MMCT
l / nm
From a magnetic point of view, the chain is
divided into small units under the irradiation of
visible light, and the long ordering at low
temperature disappeared. This process is
completely reversible.
irradiation with visible light
cmT / emu K mol1
light off
light on
T / K
Light sauce Metal-Halide lamp.
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Pressure Effect on Magnetism
Pressure medium Apiezon-J oil
5Hz
P 2.1 kbar
P 0 kbar
1000Hz
cm / emu mol-1
cm / emu mol-1
T / K
T / K
2.0K
2.0K
cm / emu mol-1
cm / emu mol-1
2.8K
2.8K
a  0.09(5)
a  0.10(5)
cm / emu mol-1
cm / emu mol-1
Brocking temp. rises under pressure
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Pressure Effect on Magnetism
0 kbar D / kB 18(1) ?
-lnt
2.1kbar D / kB 22(1) ?
Energy barrier increses under pressure
T-1 / K-1
pressure
Fe-Fe AF interaction might be strengthened by
shrinking
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Effects of Presence/Absence of Solvent
wet condition
dry condition
cT / a.u.
cT / a.u.
T / K
T / K
dry under vacuum 20min.
5Hz
5Hz
1000Hz
1000Hz
a 0.11-0.15
c / a.u.
c / a.u.
a 0.10-0.14
T / K
T / K
Presence/absence of crystalline solvnets strongly
affect on magnetism
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Effects of Presence/Absence of Solvent
dry under vacuum
Arrhenius plot
dry condition
D /kB
lnt
wet condition
add MeNO2
T-1 / K-1
Magnetism of the SCM reversibly changes by
presence/absence of solvnet considerable but
reversible structural change might occure.
Since the SCM is formed by the strict arrangement
of easy-plane, the SCM behavior is strongly
sensitive to structural perturbations
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Effects of Co(III) Doping on Fe(III) Site
when g 2
cmT / emu K mol-1
T/K
Co(III) ratio 30 15 5 2
Correlation length calc. from Co ratio 2.3 5.7 19 49
Correlation length calc. from cmT(2K) 2 4 9 25
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Effects of Co(III) Doping on Fe(III) Site
f 1kHz
doping rate
doping rate
cm / emu mol-1
cm / emu mol-1
T / K
T / K
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Effects of Co(III) Doping on Fe(III) Site
doping rate
T2.4K
cm / cmmax
-ln t
T -1/K-1
cm / cmmax
30 15 5 2
ln t -16.9 -17.1 -18.0 -17.9
D / kB 18.0 19.5 23.1 26.7
a 0.19 0.12 0.14 0.11
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Next Generation of Multi-Functional
Nano-Sciences of Advanced Metal Complexes
Magnetism
Optics
Conductivity
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