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MSM 09 Kolkata, Nov. 12
Frustrated S=3/2 Honeycomb antiferromagnet
Bi3Mn4O12(NO3)
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Spin Frustrations on Triangular Lattice Derivatives
Triangular Lattice Remove ¼ spins → Kagome Lattice
? ?
Disordered ground state in S = 1/2 triangular NiGa2S4
“Structurally Perfect S = 1/2 Kagome” Zn0.33Cu3.67(OH)6Cl2 Clinoatacamite
Cu3V2O7(OH)2 2H2O Volborthite
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Honeycomb Lattice
No magnetic frustration with nearest neighbor only
Next nearest neighbor interaction induces frustration
remove 1/3 spins → Honeycomb Lattice
J1
J1
J2
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Absence of LRO in Honeycomb AFM with J2/J1>0.16 (S=3/2)
Quantum: K. Takano, PRB 74, 140402R (2006)
Classical: S. Katsura et al., J. Stat. Phys. 42, 381 (1986) (J<0 for AF)
No example was reported so far!
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S=3/2 Honeycomb AFM Bi3Mn4O12(NO3)
Mn1, Mn2
Mn1, Mn2
Mn3, Mn4
Mn3, Mn4
NO3
NO3
• New compound synthesized by hydrothermal method
• Mn4+, S=3/2 • P3、No distortion in the honeycomb lattice
?
NO3 group with 120° bonds works as a template so that Mn ions form honeycomb lattice
c
O. Smirnova, M. Azuma et al., J. Am. Chem. Soc., 131, (2009) 8313.
J1
J1 J2
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Hydrothermal Synthesis NaBiO3+ 9Mn(NO3)2·∙6H2O dissolved in H2O was heated in a Teflon autoclave at 270˚C for 7 days
All the measurements were on the powder sample
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Plate like crystal with a hexagonal shape
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Neutron Powder Diffraction @HRPD JRR-‐3, Tokai, Japan
MnO2 present as impurity
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Magnetic Susceptibility Curie-‐Weiss like C =2.21,θ= -‐257 K
Broad maximum at around 80 K →2D AFM
Deviation of FC and ZFC data →Magnetic transition
2.5
2.0
1.5
1.0
0.5
0.0
M/H
(10-2
em
u/m
ol)
4003002001000Temperature (K)
1.8
1.7
1.6
1.5
M/H
(10-2
em
u/m
ol)
20151050Temperature (K)
1000 Oe"
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Total Specific Heat
MnO2 LRO
No long range ordering (RLO) (measured down to 0.4 K)
C/T has a maximum at around 40 K, suggestive of short range ordering
No lattice reference
400
300
200
100
0
C P (J
/ K
mol
)
200150100500
2.5
2.0
1.5
1.0
0.5
0.0
C /
T (J
/ K2 m
ol)
MnO2 LRO
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J1=30K, J2/J1~ 0.13 < 0.16 Monte Carlo Calculation
2 4 6 8 10 12
7
6
5
4
3
2
1
0
χ spi
n (10
-3em
u/m
ol M
n)
4003002001000Temperature (K)
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Anomaly in Magnetization Curves
Jump at ~6T
Magnetic ordering?
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H-‐T Phase diagram
20
15
10
5
0
µ 0H
(T)
302520151050T (K)
No-LRO (S.G.?)
Bi3Mn4O12(NO3)powder
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Field induced long range ordering! Ordered moment is 1.8 µB 1/3 of the spins don’t get ordered
~1.8 µB at 10 T
Neutron diffraction under magnetic field
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Findings and Questions
LRO is absent in the low magnetic field. Why? J2/J1=0.13, smaller than 1/6
What is the ground state? Spin glass?
What is the driving force of the field induced LRO?
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0
0.01
0.02
0.03
0.04
0.05
0.06
0.07
0.08
0 0.5 1 1.5 2 2.5 3
exp
Best Fit: J1= 30.7 K, J2/J1=0.12, Jc=0.2J1
Inclusion of interlayer coupling
Mn1, Mn2
Mn1, Mn2
Mn3, Mn4
Mn3, Mn4
NO3
NO3
Jc
8.28 Å
4.78 Å
Jc/J1=0.0"0.1 !0.2"
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Multiple Jc enhances the frustration?
Additional calculation or direct estimation of J values are necessary!
X-‐ray absorption study in progress!
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Magnetic ground state –µSR-‐
Fast relaxation without oscillation
→Static, random internal field
Spin glass like
30 K
20 K
10 K
8.5 K 7 K 2 K
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0
200
400
600
800
1000
1200
1400
0 10 20 30 40 50 60 70
ΔE=0.2 meVΔE=1.2 meV
Inte
nsity
(arb
. uni
ts)
Temperature (K)
Q=1.6 Å-1
ΔE=1.2 meV
• Short range spin correlation develops at low temperature • Spin-‐glass like behavior • Presence of (101) peak → AF Inter bi-‐layer coupling Jc • Anisotropic 3D correlations (ξab~ 8 Å, ξc~ 6 Å) •
Triple axes diffractometer TAS-2 & LTAS @ JRR-3
Neutron Powder Diffraction
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Intra-‐cluster ordering No inter-‐cluster correlation
ξab~ 8 Å
ξc~ 6 Å
Short Range Spin Correlation
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20
15
10
5
0
µ 0H
(T)
302520151050T (K)
No-LRO (S.G.?)
Bi3Mn4O12(NO3)powder
Development of the LRO
LRO
S. G.
LRO
S. G.
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1
0
Cp
(102 m
J / g
K)
50403020100Temperature (K)
Specific heat in magnetic field 1
0
Cp
(102 m
J / g
K)
50403020100Temperature (K)
9T
No transition is observed → Entropy change is small Probably because of the short range (cluster) ordering in zero field
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Magnetization of Aligned sample
Presence of ferromagnetic moment along the c-‐axis
0.4
0.3
0.2
0.1
0.0
M ( µ
B / f
.u.)
1086420
Field (104 Oe)
2K 10K 2K
10K
H=9T
c: hard axis ab plane // H
c c
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The Origin of the Field Induced LRO
LRO is stabilized because of the presence of ferromagnttic moment due to the spin canting
The particles perpendicular to the field don’t order (Consistent with the ordered moment of 1.8 µB out of 3 µB)
H=0
H=10T
SG
LRO with net moment
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Summary
Bi3Mn4O12(NO3) is the first example of frustrated honeycomb antiferromagnet
Inter layer coupling within the bi-‐layer is not negligible
The magnetic ground state is spin-‐glass like, but short range (cluster) ordering is present
Magnetic field induces long range ordering probably because of the presence of spin canting with magnetic moment along the c-‐axis
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Future Perspective Estimation of J values from structural parameters or spectroscopic measurement
Measurement on aligned sample (neutron, µSR)
Synthesis of isostructural compounds with different spin numbers Ti4+:S=0 as the specific heat reference, V4+:S=1/2, Cr4+:S=1 …
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Collaborators Inst. Chem. Res., Kyoto Univ
Nozomi Onishi Synthesis, Magnetic measurements Smirnova Olga Structure determination Yuichi Shimakawa
Yamanashi Univ.
Nobuhiro Kumada Synthesis
Kurashiki University of Science and the Arts
Yoshihiro Kusano TEM
JAEA
Masaaki Matsuda Neutron diffraction
KEK µSR
Akihiro Koda, Ryosuke Kadono
Univ. Tokyo Yukitoshi Motome MC calculation