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

J1J2

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

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

J1J2

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)

20151050Temperature (K)

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

mol

)

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)

4003002001000Temperature (K)

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 K7 K2 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

mJ

/ g K

)

50403020100Temperature (K)

Specific  heat  in  magnetic  field 1

0

Cp

(102

mJ

/ g K

)

50403020100Temperature (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)

2K10K2K

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