masaki azuma- frustrated s=3/2 honeycomb antiferromagnet bi3mn4o12(no3)

MSM 09 Kolkata, Nov. 12

Frustrated S=3/2 Honeycomb antiferromagnet

Bi3Mn4O12(NO3)

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

Honeycomb Lattice

  No magnetic frustration with nearest neighbor only

  Next nearest neighbor interaction induces frustration

remove 1/3 spins → Honeycomb Lattice

J1

J1

J2

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!

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

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

  Plate like crystal with a hexagonal shape

Neutron Powder Diffraction @HRPD JRR-‐3, Tokai, Japan

MnO2 present as impurity

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)


1000 Oe"

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

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)


Anomaly in Magnetization Curves

  Jump at ~6T

  Magnetic ordering?

H-‐T Phase diagram

20

15

10

5

0

µ 0H

(T)

302520151050T (K)

No-LRO (S.G.?)

Bi3Mn4O12(NO3)powder

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

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?

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"

Multiple Jc enhances the frustration?

  Additional calculation or direct estimation of J values are necessary!

  X-‐ray absorption study in progress!

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

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

Intra-‐cluster ordering No inter-‐cluster correlation

ξab~ 8 Å

ξc~ 6 Å

Short Range Spin Correlation

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.

1

0

Cp

(102 m

J / g

K)


Specific heat in magnetic field 1

0

Cp

(102 m

J / g

K)


9T

No transition is observed → Entropy change is small Probably because of the short range (cluster) ordering in zero field

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

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

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

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 …

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

masaki azuma- frustrated s=3/2 honeycomb antiferromagnet bi3mn4o12(no3)

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