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Magnetic properties of cubic compound Ce6Ni6P17with geometric frustrationsTo cite this article N Takeda et al 2012 J Phys Conf Ser 391 012071

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Magnetic properties of cubic compound Ce6Ni6P17

with geometric frustrations

N Takeda1 K Izumi1 H Ono2 S Yodono2 and T Nakano1

1Faculty of Engineering Niigata University Niigata 950-2181 Japan2Graduate School of Science and Technology Niigata University Niigata 950-2181 Japan

E-mail ntakedaengniigata-uacjp

Abstract We report the magnetic susceptibility and the low-temperature specific heat ofCe6Ni6P17 with geometric frustrations and La6Ni6P17 as a nonmagnetic counterpart Themagnetic susceptibility of Ce6Ni6P17 decreases monotonically with decreasing temperature andthe specific heat shows a broad peak around 14K The evaluated magnetic entropy is abouta half of Rln2 at 50 K This result suggests that the frustrations persist down to very lowtemperatures and the residual entropy originate from frustration is present

1 IntroductionRecently a cage structure has attracted much attentions Ion in a cage frequently shows local orunharmonic vibration which is conjectured to induce glass-like transport properties[1] On thecourse of researching new compounds with a cage structure we succeeded to prepare R6Ni6P17

(R=LaCe) R6Ni6P17 is reported to be a cubic compound with a space group I43m but nophysical properties is reported so far[2] The crystal structure is very unique and shown in Fig1On contrary to lots of rare-earth compounds with a cage structure where rare-earth ion is insidea cage R-ions in R6Ni6P17 form an octahedron cage encapsulating phosphorous The octahedraform bcc lattice[2] If the interaction between Ce-ions in octahedron is antiferromagnetic anoctahedron induces geometric frustrations as schematically shown in Fig2 The frustration inoctahedron is not well known compared with triangular pryrochlore and kagome lattices Asfar as we know Mo3Sb7 which is a superconductor with Tc = 23 K has a bcc lattice whichcomposed of octahedron[3] The geometric coordination is very similar to the present case ofCe6Ni6P17 The structural phase transition however releases the frustration below 50 K andhence the really frustrated ground state is not realized Theoretically the antiferromagnetic Isingmodel on a simple cubic lattice which is composed of corner-sharing octahedron is investigatedby Monte Carlo simulations[4] The simulations revealed that the system with nearest-neighbor(NN) interactions alone does not exhibit any phase transition leading to a degenerate groundstate with large residual entropy This result does not apply simply to the Ce6Ni6P17 with bcclattice but large residual entropy is expected in Ce6Ni6P17 Aside from a geometric frustration abcc lattice composed of octahedron has another interesting problem as pointed out in Mo3Sb7[3]The NN-bond is edge of octahedron and the next-nearest-neighbor (NNN) -bond is a Ce-Cedumbbell along cubic edge in Ce6Ni6P17 If antiferromagnetic interaction of NNN-bond is muchstronger than that of NN-bond dimerization of Ce-Ce dumbbell would be expected The NN-and NNN-distance for Ce6Ni6P17 are very close 4139 A and 4262 A respectively so therewould be a competition of frustration and dimmerization In this paper we present the magnetic

International Conference on Strongly Correlated Electron Systems (SCES 2011) IOP PublishingJournal of Physics Conference Series 391 (2012) 012071 doi1010881742-65963911012071

Published under licence by IOP Publishing Ltd 1

susceptibility and the specific heat of Ce6Ni6P17 with geometric flustrations and La6Ni6P17

Figure 1 The crystal structure ofR6Ni6P17 Octahedron composedof R-ions forms a bcc lattice Theedge of octahedron is the NN-bondand the R-R dumbbell along cubicedge is the NNN-bond

Figure 2 Schematic representa-tion of frustration in an octahedronIf the interaction is antiferromag-netic two spins frustrate

2 ExperimentThe samples used in the present experiments were prepared by molten Sn-flux method

with compositions varied between RNiPSn=11830 and 11850[2] The constituents inan evacuated quartz were heated up to 900 C and cooled slowly down to 400 C for 168hours followed by natural cooling in a furnace Very small single crystals were obtained aftereliminating Sn-flux by hydrochloric acid The X-ray diffraction examination exhibits a smallamount of NiP3 phase which is a normal metal[5] The lattice parameter is 10169 A forLa6Ni6P17 and 10114 A for Ce6Ni6P17 respectively These values are coincide with the reportedvalues[2] Single crystals less than 50microm were grounded and pressed to pellet The magneticsusceptibility χ(T ) was measured by a SQUID magnetometer The specific heat C(T ) wasmeasured by an adiabatic method with a 3He-cryostat

3 Results and discussionFigure 3 shows χ(T ) of La6Ni6P17 and Ce6Ni6P17 χ(T ) of La6Ni6P17 is positive and

exhibits weak temperature dependence indicating Pauli paramagnetism χ(300K) is 134times10minus4

International Conference on Strongly Correlated Electron Systems (SCES 2011) IOP PublishingJournal of Physics Conference Series 391 (2012) 012071 doi1010881742-65963911012071

2

0

002

004

006

008

01

012

014

0 50 100 150 200 250 300 350

T (K)

χ (

em

um

ol-

R)

Ce6Ni

6P

17

La6Ni

6P

17 (x10)

Figure 3 The temperature depen-dence of the magnetic susceptibil-ity of R6Ni6P17 χ(T ) of La6Ni6P17

is multiplied by 10 La6Ni6P17

is a Pauli paramagnet χ(T ) ofCe6Ni6P17 does not show a simpleCurie-Weiss law

0

05

1

15

2

0 1 2 3 4 5

T(K)

Ce6Ni

6P

17

La6Ni

6P

17

C (J

K m

ol-R

)

Figure 4 The specific heatof Ce6Ni6P17 and La6Ni6P17La6Ni6P17 is normal metal withthe electronic specific-heat coeffi-cient γ = 45 mJmolmiddotK2 and theDebye temperature of 380 K C(T )of Ce6Ni6P17 shows a Schottky-likebroad peak around 14 K implyingthe presence of frustrations Themagnetic phase transitions areevident from two small peaks at05 K and 09 K

emumol-La χ(T ) of Ce6Ni6P17 increases monotonically with decreasing temperature downto 20 K The monotonous increase down to low temperatures suggests that the presenceof frustrating spins as calculated in the antiferromagnetic triangular Ising lattice[6] Thedimmerization as expected apparently is not seen in the low-temperature behavior We analyzedthe susceptibility by χ(T ) = χ0 + C(T minus θ) The temperature-independent constant termχ0 sim 001 emumol-Ce is unknown origin The effective Bohr magneton microeff is evaluated tobe 20 sim 23microB which depends on fitting range and is slightly smaller than 254 microB of Ce3+The Weiss temperature θ is nearly equal to 0 K which indicates that the magnetic interactionis very weak or that ferromagnetic interaction and antiferromagnetic one coexist No magneticphase transition was found down to 20 K

The low-temperature specific-heat C(T ) of Ce6Ni6P17 and La6Ni6P17 is displayed in Fig4La6Ni6P17 is a normal metal with the electronic specific heat coefficient γ = 45 mJmolmiddotK2 andthe Debye temperature of 380 K C(T ) of Ce6Ni6P17 exhibits a Shottky-like anomaly with abroad peak around 14 K A Schottky-like specific heat is also calculated in typical triangularlattice[6] and previously mentioned octahedron simple cubic lattice[4] The octahedron simplecubic model predicts that the strength of magnetic interaction J is related to a peak position Tp

by J sim 05Tp The small value of Tp corresponds to the small Weiss temperature In addition to

International Conference on Strongly Correlated Electron Systems (SCES 2011) IOP PublishingJournal of Physics Conference Series 391 (2012) 012071 doi1010881742-65963911012071

3

this broad peak two sharp but small peaks were also observed which suggests magnetic phasetransitions The nature of these magnetic transitions is not clear at present J = 52 multipletof Ce3+ splits into three doublets under low point symmetry and the ground state has theentropy of Rln2 where R is gas constant We evaluated the magnetic entropy Sm and the resultis shown in Fig5 as a ratio to Rln2 The evaluated entropy at 5 K is much smaller than Rln2This result implies that Ce6Ni6P17 is really frustrate system down to very low temperatures andthe residual entropy is present

In many Ce-based compounds it is well known that the Kondo effect plays very importantroles The Kondo effect reduces the magnetic entropy and leads to heavy Fermi-liquid groundstate which has a nearly Tminusindependent large CT -value at low temperatures In many heavy-electron systems with an antiferromagnetic ground state an reduced entropy is observed as inthe present case The lowest temperature in the present study is not low enough and it isdifficult to estimate CTminusvalue at T = 0 K The shape of C(T ) and the strong TminusdependentCT however convince us to believe that the Kondo effect does not play a dominant role Thisassertion is also evident from that fact of no tendency to saturate in χ(T ) at low temperatures

0

01

02

03

04

05

06

0 1 2 3 4 5

Sm

R

ln2

T (K)

Ce6Ni

6P

17

Figure 5 The magnetic entropyper Ce-ion of Ce6Ni6P17 Theentropy is about a half of Rln2 at5 K

4 ConclusionsWe presented the magnetic susceptibility and specific heat measurements of R6Ni6P17 with

a unique crystal structure We showed that La6Ni6P17 is a normal metal and Ce6Ni6P17 is ageometrically frustrated system originated from octahedrally aligned Ce-ions We also showedthe presence of possible residual entropy of about a half of Rln2

AcknowledgmentsThis work was supported by a Grant-in-Aid for Scientific Research on Innovative AreardquoHeavy Electronrdquo (No20102004) of The Ministry of Education Culture Sports Science andTechnology Japan

References[1] Suekuni K Avila M A Umeo K and Takabatake T 2007 Phys Rev B75 195210[2] Braun D J and Jeitschko W 1978 Acta Cryst B34 2069[3] Koyama T Yamashita H Takahashi Y Kohara T Watanabe I Tabata Y and Nakamura H 2008 Phys Rev

Letters 101 126404[4] Tahara D Motoe Y Imada M 2007 J Phys Soc Jpn 76 013708[5] Takeda N Nakajo T Ono H Tatematsu K and Nakano T 2011 J Phys Soc Jpn 80 SA035[6] Wada K and Ishikawa T 1982 J Phys Soc Jpn 52 1774

International Conference on Strongly Correlated Electron Systems (SCES 2011) IOP PublishingJournal of Physics Conference Series 391 (2012) 012071 doi1010881742-65963911012071

4

susceptibility and the specific heat of Ce6Ni6P17 with geometric flustrations and La6Ni6P17

Figure 1 The crystal structure ofR6Ni6P17 Octahedron composedof R-ions forms a bcc lattice Theedge of octahedron is the NN-bondand the R-R dumbbell along cubicedge is the NNN-bond

Figure 2 Schematic representa-tion of frustration in an octahedronIf the interaction is antiferromag-netic two spins frustrate

2 ExperimentThe samples used in the present experiments were prepared by molten Sn-flux method

with compositions varied between RNiPSn=11830 and 11850[2] The constituents inan evacuated quartz were heated up to 900 C and cooled slowly down to 400 C for 168hours followed by natural cooling in a furnace Very small single crystals were obtained aftereliminating Sn-flux by hydrochloric acid The X-ray diffraction examination exhibits a smallamount of NiP3 phase which is a normal metal[5] The lattice parameter is 10169 A forLa6Ni6P17 and 10114 A for Ce6Ni6P17 respectively These values are coincide with the reportedvalues[2] Single crystals less than 50microm were grounded and pressed to pellet The magneticsusceptibility χ(T ) was measured by a SQUID magnetometer The specific heat C(T ) wasmeasured by an adiabatic method with a 3He-cryostat

3 Results and discussionFigure 3 shows χ(T ) of La6Ni6P17 and Ce6Ni6P17 χ(T ) of La6Ni6P17 is positive and

exhibits weak temperature dependence indicating Pauli paramagnetism χ(300K) is 134times10minus4

International Conference on Strongly Correlated Electron Systems (SCES 2011) IOP PublishingJournal of Physics Conference Series 391 (2012) 012071 doi1010881742-65963911012071

2

0

002

004

006

008

01

012

014

0 50 100 150 200 250 300 350

T (K)

χ (

em

um

ol-

R)

Ce6Ni

6P

17

La6Ni

6P

17 (x10)

Figure 3 The temperature depen-dence of the magnetic susceptibil-ity of R6Ni6P17 χ(T ) of La6Ni6P17

is multiplied by 10 La6Ni6P17

is a Pauli paramagnet χ(T ) ofCe6Ni6P17 does not show a simpleCurie-Weiss law

0

05

1

15

2

0 1 2 3 4 5

T(K)

Ce6Ni

6P

17

La6Ni

6P

17

C (J

K m

ol-R

)

Figure 4 The specific heatof Ce6Ni6P17 and La6Ni6P17La6Ni6P17 is normal metal withthe electronic specific-heat coeffi-cient γ = 45 mJmolmiddotK2 and theDebye temperature of 380 K C(T )of Ce6Ni6P17 shows a Schottky-likebroad peak around 14 K implyingthe presence of frustrations Themagnetic phase transitions areevident from two small peaks at05 K and 09 K

emumol-La χ(T ) of Ce6Ni6P17 increases monotonically with decreasing temperature downto 20 K The monotonous increase down to low temperatures suggests that the presenceof frustrating spins as calculated in the antiferromagnetic triangular Ising lattice[6] Thedimmerization as expected apparently is not seen in the low-temperature behavior We analyzedthe susceptibility by χ(T ) = χ0 + C(T minus θ) The temperature-independent constant termχ0 sim 001 emumol-Ce is unknown origin The effective Bohr magneton microeff is evaluated tobe 20 sim 23microB which depends on fitting range and is slightly smaller than 254 microB of Ce3+The Weiss temperature θ is nearly equal to 0 K which indicates that the magnetic interactionis very weak or that ferromagnetic interaction and antiferromagnetic one coexist No magneticphase transition was found down to 20 K

The low-temperature specific-heat C(T ) of Ce6Ni6P17 and La6Ni6P17 is displayed in Fig4La6Ni6P17 is a normal metal with the electronic specific heat coefficient γ = 45 mJmolmiddotK2 andthe Debye temperature of 380 K C(T ) of Ce6Ni6P17 exhibits a Shottky-like anomaly with abroad peak around 14 K A Schottky-like specific heat is also calculated in typical triangularlattice[6] and previously mentioned octahedron simple cubic lattice[4] The octahedron simplecubic model predicts that the strength of magnetic interaction J is related to a peak position Tp

by J sim 05Tp The small value of Tp corresponds to the small Weiss temperature In addition to

International Conference on Strongly Correlated Electron Systems (SCES 2011) IOP PublishingJournal of Physics Conference Series 391 (2012) 012071 doi1010881742-65963911012071

3

this broad peak two sharp but small peaks were also observed which suggests magnetic phasetransitions The nature of these magnetic transitions is not clear at present J = 52 multipletof Ce3+ splits into three doublets under low point symmetry and the ground state has theentropy of Rln2 where R is gas constant We evaluated the magnetic entropy Sm and the resultis shown in Fig5 as a ratio to Rln2 The evaluated entropy at 5 K is much smaller than Rln2This result implies that Ce6Ni6P17 is really frustrate system down to very low temperatures andthe residual entropy is present

In many Ce-based compounds it is well known that the Kondo effect plays very importantroles The Kondo effect reduces the magnetic entropy and leads to heavy Fermi-liquid groundstate which has a nearly Tminusindependent large CT -value at low temperatures In many heavy-electron systems with an antiferromagnetic ground state an reduced entropy is observed as inthe present case The lowest temperature in the present study is not low enough and it isdifficult to estimate CTminusvalue at T = 0 K The shape of C(T ) and the strong TminusdependentCT however convince us to believe that the Kondo effect does not play a dominant role Thisassertion is also evident from that fact of no tendency to saturate in χ(T ) at low temperatures

0

01

02

03

04

05

06

0 1 2 3 4 5

Sm

R

ln2

T (K)

Ce6Ni

6P

17

Figure 5 The magnetic entropyper Ce-ion of Ce6Ni6P17 Theentropy is about a half of Rln2 at5 K

4 ConclusionsWe presented the magnetic susceptibility and specific heat measurements of R6Ni6P17 with

a unique crystal structure We showed that La6Ni6P17 is a normal metal and Ce6Ni6P17 is ageometrically frustrated system originated from octahedrally aligned Ce-ions We also showedthe presence of possible residual entropy of about a half of Rln2

AcknowledgmentsThis work was supported by a Grant-in-Aid for Scientific Research on Innovative AreardquoHeavy Electronrdquo (No20102004) of The Ministry of Education Culture Sports Science andTechnology Japan

References[1] Suekuni K Avila M A Umeo K and Takabatake T 2007 Phys Rev B75 195210[2] Braun D J and Jeitschko W 1978 Acta Cryst B34 2069[3] Koyama T Yamashita H Takahashi Y Kohara T Watanabe I Tabata Y and Nakamura H 2008 Phys Rev

Letters 101 126404[4] Tahara D Motoe Y Imada M 2007 J Phys Soc Jpn 76 013708[5] Takeda N Nakajo T Ono H Tatematsu K and Nakano T 2011 J Phys Soc Jpn 80 SA035[6] Wada K and Ishikawa T 1982 J Phys Soc Jpn 52 1774

International Conference on Strongly Correlated Electron Systems (SCES 2011) IOP PublishingJournal of Physics Conference Series 391 (2012) 012071 doi1010881742-65963911012071

4

0

002

004

006

008

01

012

014

0 50 100 150 200 250 300 350

T (K)

χ (

em

um

ol-

R)

Ce6Ni

6P

17

La6Ni

6P

17 (x10)

Figure 3 The temperature depen-dence of the magnetic susceptibil-ity of R6Ni6P17 χ(T ) of La6Ni6P17

is multiplied by 10 La6Ni6P17

is a Pauli paramagnet χ(T ) ofCe6Ni6P17 does not show a simpleCurie-Weiss law

0

05

1

15

2

0 1 2 3 4 5

T(K)

Ce6Ni

6P

17

La6Ni

6P

17

C (J

K m

ol-R

)

Figure 4 The specific heatof Ce6Ni6P17 and La6Ni6P17La6Ni6P17 is normal metal withthe electronic specific-heat coeffi-cient γ = 45 mJmolmiddotK2 and theDebye temperature of 380 K C(T )of Ce6Ni6P17 shows a Schottky-likebroad peak around 14 K implyingthe presence of frustrations Themagnetic phase transitions areevident from two small peaks at05 K and 09 K

emumol-La χ(T ) of Ce6Ni6P17 increases monotonically with decreasing temperature downto 20 K The monotonous increase down to low temperatures suggests that the presenceof frustrating spins as calculated in the antiferromagnetic triangular Ising lattice[6] Thedimmerization as expected apparently is not seen in the low-temperature behavior We analyzedthe susceptibility by χ(T ) = χ0 + C(T minus θ) The temperature-independent constant termχ0 sim 001 emumol-Ce is unknown origin The effective Bohr magneton microeff is evaluated tobe 20 sim 23microB which depends on fitting range and is slightly smaller than 254 microB of Ce3+The Weiss temperature θ is nearly equal to 0 K which indicates that the magnetic interactionis very weak or that ferromagnetic interaction and antiferromagnetic one coexist No magneticphase transition was found down to 20 K

The low-temperature specific-heat C(T ) of Ce6Ni6P17 and La6Ni6P17 is displayed in Fig4La6Ni6P17 is a normal metal with the electronic specific heat coefficient γ = 45 mJmolmiddotK2 andthe Debye temperature of 380 K C(T ) of Ce6Ni6P17 exhibits a Shottky-like anomaly with abroad peak around 14 K A Schottky-like specific heat is also calculated in typical triangularlattice[6] and previously mentioned octahedron simple cubic lattice[4] The octahedron simplecubic model predicts that the strength of magnetic interaction J is related to a peak position Tp

by J sim 05Tp The small value of Tp corresponds to the small Weiss temperature In addition to

International Conference on Strongly Correlated Electron Systems (SCES 2011) IOP PublishingJournal of Physics Conference Series 391 (2012) 012071 doi1010881742-65963911012071

3

this broad peak two sharp but small peaks were also observed which suggests magnetic phasetransitions The nature of these magnetic transitions is not clear at present J = 52 multipletof Ce3+ splits into three doublets under low point symmetry and the ground state has theentropy of Rln2 where R is gas constant We evaluated the magnetic entropy Sm and the resultis shown in Fig5 as a ratio to Rln2 The evaluated entropy at 5 K is much smaller than Rln2This result implies that Ce6Ni6P17 is really frustrate system down to very low temperatures andthe residual entropy is present

In many Ce-based compounds it is well known that the Kondo effect plays very importantroles The Kondo effect reduces the magnetic entropy and leads to heavy Fermi-liquid groundstate which has a nearly Tminusindependent large CT -value at low temperatures In many heavy-electron systems with an antiferromagnetic ground state an reduced entropy is observed as inthe present case The lowest temperature in the present study is not low enough and it isdifficult to estimate CTminusvalue at T = 0 K The shape of C(T ) and the strong TminusdependentCT however convince us to believe that the Kondo effect does not play a dominant role Thisassertion is also evident from that fact of no tendency to saturate in χ(T ) at low temperatures

0

01

02

03

04

05

06

0 1 2 3 4 5

Sm

R

ln2

T (K)

Ce6Ni

6P

17

Figure 5 The magnetic entropyper Ce-ion of Ce6Ni6P17 Theentropy is about a half of Rln2 at5 K

4 ConclusionsWe presented the magnetic susceptibility and specific heat measurements of R6Ni6P17 with

a unique crystal structure We showed that La6Ni6P17 is a normal metal and Ce6Ni6P17 is ageometrically frustrated system originated from octahedrally aligned Ce-ions We also showedthe presence of possible residual entropy of about a half of Rln2

AcknowledgmentsThis work was supported by a Grant-in-Aid for Scientific Research on Innovative AreardquoHeavy Electronrdquo (No20102004) of The Ministry of Education Culture Sports Science andTechnology Japan

References[1] Suekuni K Avila M A Umeo K and Takabatake T 2007 Phys Rev B75 195210[2] Braun D J and Jeitschko W 1978 Acta Cryst B34 2069[3] Koyama T Yamashita H Takahashi Y Kohara T Watanabe I Tabata Y and Nakamura H 2008 Phys Rev

Letters 101 126404[4] Tahara D Motoe Y Imada M 2007 J Phys Soc Jpn 76 013708[5] Takeda N Nakajo T Ono H Tatematsu K and Nakano T 2011 J Phys Soc Jpn 80 SA035[6] Wada K and Ishikawa T 1982 J Phys Soc Jpn 52 1774

International Conference on Strongly Correlated Electron Systems (SCES 2011) IOP PublishingJournal of Physics Conference Series 391 (2012) 012071 doi1010881742-65963911012071

4

this broad peak two sharp but small peaks were also observed which suggests magnetic phasetransitions The nature of these magnetic transitions is not clear at present J = 52 multipletof Ce3+ splits into three doublets under low point symmetry and the ground state has theentropy of Rln2 where R is gas constant We evaluated the magnetic entropy Sm and the resultis shown in Fig5 as a ratio to Rln2 The evaluated entropy at 5 K is much smaller than Rln2This result implies that Ce6Ni6P17 is really frustrate system down to very low temperatures andthe residual entropy is present

In many Ce-based compounds it is well known that the Kondo effect plays very importantroles The Kondo effect reduces the magnetic entropy and leads to heavy Fermi-liquid groundstate which has a nearly Tminusindependent large CT -value at low temperatures In many heavy-electron systems with an antiferromagnetic ground state an reduced entropy is observed as inthe present case The lowest temperature in the present study is not low enough and it isdifficult to estimate CTminusvalue at T = 0 K The shape of C(T ) and the strong TminusdependentCT however convince us to believe that the Kondo effect does not play a dominant role Thisassertion is also evident from that fact of no tendency to saturate in χ(T ) at low temperatures

0

01

02

03

04

05

06

0 1 2 3 4 5

Sm

R

ln2

T (K)

Ce6Ni

6P

17

Figure 5 The magnetic entropyper Ce-ion of Ce6Ni6P17 Theentropy is about a half of Rln2 at5 K

4 ConclusionsWe presented the magnetic susceptibility and specific heat measurements of R6Ni6P17 with

a unique crystal structure We showed that La6Ni6P17 is a normal metal and Ce6Ni6P17 is ageometrically frustrated system originated from octahedrally aligned Ce-ions We also showedthe presence of possible residual entropy of about a half of Rln2

AcknowledgmentsThis work was supported by a Grant-in-Aid for Scientific Research on Innovative AreardquoHeavy Electronrdquo (No20102004) of The Ministry of Education Culture Sports Science andTechnology Japan

References[1] Suekuni K Avila M A Umeo K and Takabatake T 2007 Phys Rev B75 195210[2] Braun D J and Jeitschko W 1978 Acta Cryst B34 2069[3] Koyama T Yamashita H Takahashi Y Kohara T Watanabe I Tabata Y and Nakamura H 2008 Phys Rev

Letters 101 126404[4] Tahara D Motoe Y Imada M 2007 J Phys Soc Jpn 76 013708[5] Takeda N Nakajo T Ono H Tatematsu K and Nakano T 2011 J Phys Soc Jpn 80 SA035[6] Wada K and Ishikawa T 1982 J Phys Soc Jpn 52 1774

International Conference on Strongly Correlated Electron Systems (SCES 2011) IOP PublishingJournal of Physics Conference Series 391 (2012) 012071 doi1010881742-65963911012071

4