Effects of oxygen content on Bi3Mn3O 11+Δ: From 45 K Antiferromagnetism to Room-Temperature True Ferromagnetism

Article abstract of DOI:10.1021/ja1043598

The effects of oxygen content on the structural, physical, and chemical properties of Bi₃Mn₃O₁₁ with KSbO ₃-type structure have been investigated. It was found that the oxygen content in Bi₃Mn₃O_11+Δ can vary over a wide Δ range, keeping the same cubic structure (space group Pn3, a = 9.12172(5) A for Δ = -0.5, a = 9.13784(8) A for Δ = 0, and a = 9.09863(7) A for Δ = 0.6) and semiconducting properties of the material. At the same time, magnetic properties change from true antiferromagnetic with T_N = 45 K for Δ = -0.5 to true ferromagnetic with T_C = 307 K for Δ = +0.6. Bi ₃Mn₃O₁₁ (Δ = 0) shows ferrimagnetic-like properties with T_C = 150 K and features typical for a re-entrant spin-glass below 30 K. Noticeable changes of the magnetic transition temperature and magnetism in Bi₃Mn₃O_11+Δ with Δ can be compared with changes of the magnetic and electronic properties of LaMnO_3+Δ, BiMnO_3+Δ, high-temperature copper superconductors (e.g., YBa₂Cu₃O_7+Δ), and other cuprates. Bi₃Mn₃O_11.6 shows a new record high T_C among insulating/semiconducting true ferromagnets. Our results demonstrate that the oxygen content can vary for the same cation composition in KSbO₃-type materials, and the oxygen content can be increased up to BiMnO_3.867 (Bi₃Mn₃O _11.6).

Full text of DOI:10.1021/ja1043598

Published on Web 08/13/2010
Effects of Oxygen Content on Bi Mn O11+δ: From 45 K
3
3
Antiferromagnetism to Room-Temperature True
Ferromagnetism
Alexei A. Belik* and Eiji Takayama-Muromachi
International Center for Materials Nanoarchitectonics, National Institute for Materials Science,
1
-1 Namiki, Tsukuba, Ibaraki 305-0044, Japan
Received May 19, 2010; E-mail: alexei.belik@nims.go.jp
Abstract: The effects of oxygen content on the structural, physical, and chemical properties of Bi
3
Mn
3
O
11
with KSbO
3
-type structure have been investigated. It was found that the oxygen content in Bi
3
Mn
3
O
11+δ
j
can vary over a wide δ range, keeping the same cubic structure (space group Pn3, a ) 9.12172(5) Å for
δ ) -0.5, a ) 9.13784(8) Å for δ ) 0, and a ) 9.09863(7) Å for δ ) 0.6) and semiconducting properties
of the material. At the same time, magnetic properties change from true antiferromagnetic with T
for δ ) -0.5 to true ferromagnetic with T ) 307 K for δ ) +0.6. Bi Mn 11 (δ ) 0) shows ferrimagnetic-
like properties with T ) 150 K and features typical for a re-entrant spin-glass below 30 K. Noticeable
changes of the magnetic transition temperature and magnetism in Bi Mn 11+δ with δ can be compared
with changes of the magnetic and electronic properties of LaMnO3+δ, BiMnO3+δ, high-temperature copper
superconductors (e.g., YBa Cu 7+δ), and other cuprates. Bi Mn 11.6 shows a new record high T among
insulating/semiconducting true ferromagnets. Our results demonstrate that the oxygen content can vary
N
) 45 K
C
3
3
O
C
3
3
O
2
3
O
3
3
O
C
for the same cation composition in KSbO
Mn
3
-type materials, and the oxygen content can be increased up to
BiMnO3.867 (Bi
3
3
O11.6).
1
. Introduction
ABO compounds crystallize in a number of structure types,
the corner- and edge-shared SbO octahedra forming a three-
dimensional framework with channels. The channels are filled
6
3
3
+
with K ions in KSbO
Bi Ru ·3RuO
filling of the channels by K ions in KBiO
3
(K·SbO
3 3 2
) and with Bi O units in
including perovskite, pyroxene, corundum, ilmenite (ordered
corundum), hexagonal manganites, bixbyite, rare earth sesqui-
3
3
O
11 (Bi
3
O
2
3
) in an ordered manner. Disordered
+
14
+
1
3
,
Na ions in
oxide structures, PbReO
KSbO
of representatives, e.g., KSbO
Bi
La
materials is quite interesting because the oxygen content changes
from ABO to ABO3.667. The KSbO -type structure is built from
3
, KSbO
3
, AlFeO
3
, and others. The
1
5
2+
9
j
NaSbO , and Sr ions in Sr Re O resulted in space group
-type family (space group Pn3) has only about a dozen
3
2
3
9
3
2
3,4
8
j
Im3. The channels can also be filled by other units, e.g. La
forming La Ru O·6RuO ) and related compounds
19 that deviate from the A:B ) 1:1 stoichiometry and
4
O,
3
, KIrO
3
,
3 2 11
Bi GaSb O ,
4
5
6-8
9
AlSb
2
O
11, Bi
2
NaSb
and Pb
3
O
6
11, Bi
3
M
3
O11 (M ) Ru,
Re, Os ),
4
6
O19 (La
4
3
3
1
0-12
13
9
Ru
3
O
11
,
Re
6
O
19
.
Nevertheless, this class of
La
have a different space group of I23.
content for the same cation composition have not been reported
for the KSbO -type materials, even though some of them have
d and 5d transition metals with variable oxidation states. The
4 6
M O
3
11,12
Variations in the oxygen
3
3
3
(
(
(
(
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4
2) Hoppe, R.; Claes, K. J. Less-Common Metals 1975, 43, 129.
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on the properties of materials, e.g., on magnetic and electronic
properties of high-temperature copper superconductors (e.g.,
1
998, 108, 649. (b) Ismunandar; Kennedy, B. J.; Hunter, B. A. J. Solid
State Chem. 1996, 127, 178.
16
17,18
19-21
YBa
2
Cu
3
O
7+δ) orperovskites(e.g.,LaMnO3+δ
,
BiMnO3+δ,
(
(
5) Champarnaud-Mesjard, J. C.; Frit, B.; Aftati, A.; El Farissi, M. Eur.
J. Solid State Inorg. Chem. 1995, 32, 495.
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4
2
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Mater. 1993, 5, 1273.
5.
(
(
(
7) Tsuchida, K.; Kato, C.; Fujita, T.; Kobayashi, Y.; Sato, M. J. Phys.
Soc. Jpn. 2004, 73, 698.
(15) Hong, H. Y.-P.; Kafalas, J. A.; Goodenough, J. B. J. Solid State Chem.
1974, 9, 345.
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B 2003, 329, 743.
(16) Strobel, P.; Capponi, J. J.; Chaillout, C.; Marezio, M.; Tholence, J. L.
Nature 1987, 327, 306.
9) Suzuki, H.; Ozawa, H.; Sato, H. J. Phys. Soc. Jpn. 2007, 76, 044805.
(17) Topfer, J.; Goodenough, J. B. J. Solid State Chem. 1997, 130, 117.
(18) Maurin, I.; Barboux, P.; Lassailly, Y.; Boilot, J. P.; Villain, F.; Dordor,
P. J. Solid State Chem. 2001, 160, 123.
(
(
10) (a) Cotton, F. A.; Rice, C. E. J. Solid State Chem. 1978, 25, 137. (b)
Abraham, F.; Trehoux, J.; Thomas, D. Mater. Res. Bull. 1978, 13,
8
05.
(19) Sundaresan, A.; Mangalam, R. V. K.; Iyo, A.; Tanaka, Y.; Rao,
C. N. R. J. Mater. Chem. 2008, 18, 2191.
11) Khalifah, P.; Nelson, K. D.; Jin, R.; Mao, Z. Q.; Liu, Y.; Huang, Q.;
Gao, X. P. A.; Ramirez, A. P.; Cava, R. J. Nature 2001, 411, 669.
12) Khalifah, P.; Cava, R. J. Phys. ReV. B 2001, 64, 085111.
13) Abakumov, A. M.; Shpanchenko, R. V.; Antipov, E. V. Z. Anorg.
Allg. Chem. 1998, 624, 750.
(20) Belik, A. A.; Kolodiazhnyi, T.; Kosuda, K.; Takayama-Muromachi,
E. J. Mater. Chem. 2009, 19, 1593.
(
(
(21) Belik, A. A.; Kodama, K.; Igawa, N.; Shamoto, S.; Kosuda, K.;
Takayama-Muromachi, E. J. Am. Chem. Soc. 2010, 132, 8137.
1
2426 9 J. AM. CHEM. SOC. 2010, 132, 12426–12432
10.1021/ja1043598  2010 American Chemical Society

Effects of Oxygen Content on Properties of Bi
Mn O
3 3 11+δ
A R T I C L E S
2
2
17,18
and (BiMn
3
)Mn
4
O
12). In LaMnO3+δ
,
the change in δ
results in changes from an antiferromagnetic insulator to a
ferromagnetic insulator to a ferromagnetic metal; at the same
time, crystal symmetries are also changed.
Recently, we have succeeded in preparing the first example
of a KSbO
namely, Bi
3
-type material containing a 3d transition metal,
23
3
3 11
Mn O .
3 3
Bi Mn O11 shows quite interesting mag-
netic properties: a ferrimagnetic-like transition near 150 K with
features typical for re-entrant spin-glass below 30 K. We have
also demonstrated the possibility of forming oxygen-deficient
2
3
Bi
of Bi
In this work, we demonstrate for the first time that the oxygen
content of the KSbO -type materials can be increased further
Mn ), meaning that
3
Mn
3
O
3
11-δ samples by heating Bi
3
Mn
3
O
11
.
The properties
3
Mn
O
11-δ and Bi Mn 11+δ have not been determined yet.
3
3
O
3
up to ABO3.867 in Bi
3
3
O11.6 (Bi
3
O
2.6 ·3MnO
3
Figure 1. Thermogravimetric curves of Bi
blue and green curves) and Bi Mn
a heating rate of 5 K/min. Note that the weight loss is given in δ for
Bi Mn Mn
3
Mn
3
O
11 (two different samples,
there is additional space in the channels of the structure. We
also show that the oxygen content can vary for the same cation
3
3
O11.6 (black curve) in high-purity Ar at
composition in KSbO
3
-type materials. A wide variation of δ in
3
3
O11+δ and Bi
3
3 11.6+δ
O .
Bi Mn 11(δ keeps the same cubic structure and semiconducting
3
3
O
properties of the material, compared, for example, with perov-
skites. At the same time, magnetic properties change from
3 3 11.6
Bi Mn O was prepared using the same synthesis conditions
from stoichiometric mixtures of Bi O , MnO , and Bi O4.20, taken
2 3 2 2
antiferromagnetic with T
ferromagnetic with T ) 307 K for δ ) +0.6. Bi
shows a new record high ferromagnetic Curie temperature (T
N
) 45 K for δ ) -0.5 to true
3 3
for the target composition of Bi Mn O12 according to the following
reaction:
C
3
Mn
3 11.6
O
C
)
2
4
among insulating/semiconducting true ferromagnets.
. Experimental Section
.1. Synthesis and Determination of the Composition. Bi
0.25Bi O + 3MnO + 1.25Bi O
4.20
f
2
3
2
2
Bi Mn O + 0.2O2 (2)
3
3
11.6
2
2
3
-
The weight of Pt capsules after the synthesis changed noticeably,
indicating that the Pt capsules were not able to maintain the
generated oxygen pressure, and some oxygen escaped from the Pt
capsules.
Mn
(
3
O
11 was prepared from stoichiometric mixtures of Bi
99.9999%, Rare Metallic Co. Ltd.), MnO (99.997%, Alfa Aesar),
and Bi 4.20 (99%, High Purity Chemicals Ltd.) according to the
following reaction:
2 3
O
2
2
O
2
3
The oxygen content of the final products was determined by TGA
in a mixture of 3% H
2
+ 97% Ar using a Perkin-Elmer Pyris 1
1
3/12Bi O + 3MnO + 5/12Bi O
f Bi Mn O
4.20 3 3 11
2
3
2
2
TGA system in Al
2
O holders (the samples were heated to 873 K
3
(
1)
at a heating rate of 5 K/min and soaked there for 1 h). The samples
decomposed to mixtures of Bi and MnO. The calculated oxygen
content was Bi Mn O11.00(1) and Bi Mn O11.60(1) (see the Supporting
3 3 3 3
Information). We note that the oxygen content determination by
TGA or other chemical methods is based on certain assumptions,
as discussed in ref 20. If some assumptions are not kept, a
systematic shift may result. For example, the presence of impurities
will affect the results of both TGA and (iodometric) titration
techniques.
The phase purity and oxygen content of MnO
by X-ray powder diffraction (XRD) and thermogravimetric analysis
TGA). MnO was the well-crystallized single-phase R modification.
MnO was heated in air to 923 K over 5 h and soaked there for
4 h (the experiment was performed in a conventional muffle
2
were confirmed
(
2
2
2
furnace; the sample weights were measured before and after
annealing). The final product was well-crystallized single-phase
Mn
corresponded to MnO2.01(1). The oxygen content of a commercial
2 5
Bi was found to be Bi 4.20(2) by TGA. The commercial Bi O
2 3
O . The oxygen content calculated from the weight loss
The Bi
was prepared from Bi
K and cooled to room temperature inside an oven in a magnetometer
Quantum Design MPMS). The average heating/cooling rate was
about 1.5 K/min. Inside the oven, vacuum conditions were kept
about 1.3 kPa). Bi Mn ∼10.5 can also be prepared from
Bi Mn Mn 11.6 by heating to 750-770 K in high-
3
Mn
3
O
10.5 sample (used for the property measurements)
3
Mn Mn 11.60 was heated to 750
3
O
11.60. Bi
3
3
O
2
O
5
2
O
was heated in an SII Exstar 6000 (TG-DTA 6200) system to 770
K (10 K/min, Pt holder) in air, and the weight loss gave the
composition of Bi
treatment was well-crystallized single-phase Bi
The synthesis of Bi Mn 11 according to reaction 1 was
performed in a belt-type high-pressure apparatus at 6 GPa and 1600
K for 40 min in Pt capsules. After heat treatment, the samples
were quenched to room temperature, and the pressure was slowly
released. The resultant samples were dense black pellets. No
noticeable change in the weight of the Pt capsules was found after
the synthesis, indicating that the target oxygen content did not
change during the reaction.
(
2
O4.20(2). The final product after the TGA heat
(
3
3
O
O .
2 3
O11.0 and Bi
3
3
O
3
3
O
3
3
purity Ar (at a heating rate of 5 K/min and soaking time of 1 h)
(Figure 1).
2
3
3 3 3
The cation ratio of Bi Mn O11 and BiMnO (used for comparison)
was determined by electron probe microanalysis (EPMA) using a
JEOL JXA-8500F instrument. The surface was polished on a fine
alumina (1 µm)-coated film before the EPMA measurements. MnO
and Bi
Mn:Bi ratio determined by EPMA was 1.05(2) in Bi
1.05(6) in BiMnO
4 3
Ge O12 were used as standard materials for Mn and Bi. The
3
Mn
3
O11 and
(
22) (a) Imamura, N.; Karppinen, M.; Motohashi, T.; Fu, D.; Itoh, M.;
Yamauchi, H. J. Am. Chem. Soc. 2008, 130, 14948. (b) Imamura, N.;
Karppinen, M.; Yamauchi, H. Chem. Mater. 2009, 21, 2179.
3
.
2.2. Physical Properties. XRD data were collected at room
temperature on a RIGAKU Ultima III diffractometer using Cu KR
radiation (2θ range of 10-120°, step width of 0.02°, and counting
(
23) Belik, A. A.; Takayama-Muromachi, E. J. Am. Chem. Soc. 2009, 131,
9
504.
time of 10 s/step). Synchrotron XRD data for Bi
3 3
Mn O10.50 and
(
24) Rogado, N. S.; Li, J.; Sleight, A. W.; Subramanian, M. A. AdV. Mater.
2
005, 17, 2225.
Bi Mn 11.60 were collected at room temperature using a large
3
3
O
J. AM. CHEM. SOC. 9 VOL. 132, NO. 35, 2010 12427

A R T I C L E S
Belik and Takayama-Muromachi
3 3 3 3 3 3
Figure 2. X-ray powder diffraction patterns (measured with Cu KR radiation at room temperature) of Bi Mn O10.5, Bi Mn O11.6, and Bi Mn O11. The
j
3 3 11
refined lattice parameters are given. Possible Bragg reflections (space group Pn3) are indicated by tic marks for Bi Mn O .
2
5
Debye-Scherrer camera at the BL02B2 beamline of SPring-8.
The incident beam from a bending magnet was monochromatized
to λ ) 0.41916 Å. The samples were contained in (boro)glass
capillary tubes with an inner diameter of 0.2 mm, and the capillary
tubes were rotated during measurements. The synchrotron XRD
data were collected in a 2θ range from 1° to 75° with a step interval
of 0.01° (the data from 2.5° to 52.5° were used in the refinements).
Laboratory XRD and synchrotron XRD data were analyzed by the
of Bi
frequency range from 100 Hz to 1 MHz; no anomalies were detected
near T (see the Supporting Information).
3 3
Mn O10.5 were performed between 5 and 300 K in the
N
3
. Results
3.1. X-ray Powder Diffraction of Bi
and Bi Mn O . Figure 2 depicts XRD patterns of Bi Mn O10.5,
3 3 3 3 11
Mn O10.5, Bi Mn O ,
3
3
11.6
3
3
26
Rietveld method with RIETAN-2000 software. High-temperature
synchrotron XRD data of Bi Mn 11 were collected at the BL02B2
beamline with λ ) 0.77412 Å.
Magnetic susceptibilities, ꢀ ) M/H, of Bi
3 3 11 3 3
Bi Mn O , and Bi Mn O11.6. All the samples were almost
3
3
O
single-phase with traces of unidentified impurities. Bi
crystallize in the KSbO -type structure (space group Pn3) with
a ) 9.12172(5) Å (δ ) -0.5), 9.13784(8) Å (δ ) 0), and
.09863(7) Å (δ ) 0.6). A non-monotonic change of the lattice
3 11(δ
Mn O
3
j
3
3
3
Mn O11(δ were
measured on a SQUID magnetometer (Quantum Design, MPMS)
between 2 and 400 K in applied fields of 100 Oe, 1 kOe, and 10
kOe under both zero-field-cooled (ZFC) and field-cooled (FC; on
cooling) conditions. The measurements between 300 and 750 K
were performed using an oven attachment on heating and cooling
at 10 kOe. Isothermal magnetization measurements were performed
at 5, 100, 200, 300, and 350 K between -50 and 50 kOe and
between 270 and 350 K with a step of 2 K from 50 to 0 kOe for
9
parameter with δ is probably the combination of different
effects: contraction of the unit cell due to the increased amount
of Mn5 and expansion of the unit cell due to the increased
number of oxygen ions in the channels. A non-monotonic
change of the lattice parameter was also observed during in situ
+
23
high-temperature synchrotron XRD measurements, where the
a parameter first jumps in Bi Mn 10.9 compared with
Bi Mn 11 and then drops in Bi Mn 10.5 (see also the Sup-
porting Information).
Bi
on the 100 Oe dꢀ/dT vs T and d(ꢀT)/dT vs T curves, respectively.
The specific heat, C , at magnetic fields of 0 and 70 kOe was
3 3 C N
Mn O11.6. T and T were roughly defined by the peak positions
3
3
O
3
3
O
3
3
O
p
recorded between 2 and 300 K (using an N Apiezon grease to make
good thermal contacts between sample and holder) and between
50 and 400 K (using an H Apiezon grease) on cooling by a pulse
relaxation method using a commercial calorimeter (Quantum Design
PPMS).
Direct current (dc) electrical resistivity was measured between
3
.2. Crystal Structure Analysis of Bi
3
Mn
3
O
10.5 and Bi
3
Mn
11 were used as initial ones
Mn Mn
Fractional coordinates of the Bi1 site in Bi 11.6 were refined
using a constraint z ) y (similar to Bi Mn
3 11.6
O .
23
3 3
Fractional coordinates of Bi Mn O
in the crystal structure analysis of Bi
2
3
3
O
10.5 and Bi
Mn
3
O
3
3 11.6
O .
3
3
O
2
3
3
11), even though
the Bi1 site is located in a general position (x,y,z). This constraint
was used because the y and z coordinates were the same within
standard deviations, and estimated standard deviations of y and
z were about 1 order of magnitude larger when the y and z
coordinates were refined independently. On the other hand, the
x, y, and z coordinates of the Bi1 site could be refined in
1
0 and 400 K by the conventional four-probe method using a
Quantum Design PPMS with the dc-gage current of 2 mA. The
dc-gage current was reduced automatically at low temperatures to
allow the resistivity measurements. Resistivity became too high to
be measured with our system below 300 K for Bi
for Bi Mn 11, and 180 K for Bi Mn 11.6. At 300 K, Bi Mn O
3 3 11.6
showed an almost linear increase of resistivity as a function of
magnetic field, reaching about a 15% increase at 90 kOe (see the
3 3
Mn O10.5, 130 K
3
3
O
3
3
O
Bi
3
Mn
3
O10.5. Attempts to split the Bi2 atom from the 4b site to
the 8e site were unsuccessful in Bi
3
Mn 11 and Bi Mn O
3
O
3
3 11.6
Supporting Information). Pellets with approximate sizes of 5 × 2
3
(the x coordinate was almost zero, and the estimated standard
deviation was huge). On the other hand, the Bi2 site was
×
1 mm were used for the measurements. Dielectric measurements
successfully split in Bi
of 1 for the O1, O2, and O3 sites, the thermal parameters (B)
were normal in Bi Mn 11.6, while B(O1) converged to 8.5(6)
10.5. This fact shows that the oxygen vacancies
3 3
Mn O10.5. With an occupation factor (g)
(
25) Nishibori, E.; Takata, M.; Kato, K.; Sakata, M.; Kubota, Y.; Aoyagi,
S.; Kuroiwa, Y.; Yamakata, M.; Ikeda, N. Nucl. Instrum. Methods
Phys. Res. Sect. A 2001, 467-468, 1045.
3
3
O
2
(
26) Izumi, F.; Ikeda, T. Mater. Sci. Forum 2000, 321-324, 198.
3 3
Å in Bi Mn O
1
2428 J. AM. CHEM. SOC. 9 VOL. 132, NO. 35, 2010

Effects of Oxygen Content on Properties of Bi
Mn O
3 3 11+δ
A R T I C L E S
Table 1. Structure Parameters of Bi
3 3
Mn O10.5 and Bi
3
Mn
3
O11.6 at
a
Room Temperature
Wyckoff
site position
2
g
x
y
z
B (Å )
3 3 10.5
Bi Mn O
Bi1
Bi2
Mn
O1
O2
O3
24h
8e
12g
8e
12f
24h
1/3
1/2
1
0.4164(3)
0.0091(2)
0.4041(3)
0.3879(6)
) x
0.3736(5)
) x
1.62(5)
0.84(3)
0.30(4)
1.0(4)
0.75
0.25
0.75 0.1456(8)
1
1
) x
) x
0.25
0.6163(11) 0.25
0.5841(8)
0.9(2)
0.2500(7)
0.5435(11) 1.2(2)
Bi
3
Mn
3 11.6
O
Bi1
Bi2
Mn
O1
O2
O3
24h
4b
12g
8e
12f
24h
1/3
1
1
1
1
0.4009(2)
0
0.4044(2)
0.1455(4)
0.6147(8)
0.5908(6)
0.38175(13) ) y
0.61(2)
0.730(11)
0.46(3)
0.4(2)
0.67(14)
0.62(13)
0
0
0.75
) x
0.25
) x
0.25
0.5403(8)
0.25
0.2445(5)
1
a
j
Mn
Space group is Pn3 (No. 201) at origin choice 2, Z ) 4. g is the
occupation factor. Bi
Å , Rwp ) 4.46%, R
3
3
O
10.5: a ) 9.11919(8) Å and V ) 758.348(11)
3
p
) 3.22%, R ) 6.99%, and R ) 7.95%.
B
F
d(Mn-O2) ) 1.860(6) Å × 2, d(Mn-O3) ) 1.886(10) Å × 2,
d(Mn-O3) ) 1.976(10) Å × 2. Bi
3
Mn
) 2.28%, R
3
O
11.6: a ) 9.11151(6) Å and V
3
)
756.434(9) Å , Rwp ) 3.44%, R
p
B
) 1.96%, and R )
F
1
.81%. d(Mn-O2) ) 1.871(4) Å × 2, d(Mn-O3) ) 1.908(6) Å × 2,
d(Mn-O3) ) 1.912(7) Å × 2.
are located at the O1 site in Bi
obtained during the structural analysis of Bi
3
Mn
3
O
10.5. The same result was
Mn 11 using in
situ high-temperature synchrotron XRD data at 740 K, where
the oxygen content was close to Bi Mn 10.5 (see the Supporting
Information of ref 23). Using synchrotron XRD data, we could
not localize additional oxygen atoms in Bi Mn
structural parameters, R indexes, and Mn-O bond lengths of
Bi Mn Mn 11.6 at room temperature are listed in
Table 1. Figure 3 shows fragments of the crystal structure of
Bi Mn 10.5. The Supporting Information gives other bond
3
3
O
3
3
O
3
3
O11.6. Final
Figure 3. Fragments of the crystal structure of Bi
Bi1 and Bi2 atoms. The MnO
in the channels are given by black circles. (a) The view along the channel
111) direction. (b) The view along the a axis.
3 3
Mn O10.5 with the split
6
octahedra are shown in gray. The O1 atoms
3
3
O
10.5 and Bi
3
3
O
(
3
3
O
lengths and observed, calculated, and difference synchrotron
XRD patterns.
3
.3. Magnetic Properties of Bi
Mn 11.6. Figure 4 shows the inverse magnetic susceptibilities
as a function of temperature (ꢀ vs T) for three samples and
3 3 3 3
Mn O10.5, Bi Mn O11, and
Bi
3
3
O
-1
actually one of the preparation routes for Bi
3
Mn
3
O
10.5. The
2
curves were fit by the simple Curie-Weiss equation (ꢀ ) µeff
/
[
8(T - θ)]) between 400 and 550 K. The effective magnetic
moment (µeff) per formula unit (f.u.) and the Curie-Weiss
temperature (θ) were calculated as follows: µeff ) 5.84 µ and
θ ) +217 K in Bi Mn 11 (the expected magnetic moment,
exp, is 6.16 µ ); µeff ) 5.37 µ and θ ) +337 K in Bi Mn
exp ) 5.57 µ ); and µeff ) 6.58 µ and θ ) -80 K in
10.5 (µexp ) 6.70 µ ). The changes in the experimental
eff values are in very good agreement with the changes of the
B
3
3
O
µ
B
B
3
3 11.6
O
(
µ
B
B
Bi
3
Mn
3
O
B
µ
4
+
4+
5+
oxidations states of Mn atoms (Bi
3
+
Mn
3
O
2
O
10.5, Bi
3
Mn
11.5). This fact also
shows that Mn ions are responsible for the charge compensation
in Bi Mn 11(δ, not Bi ions. Bi Mn 11.6 demonstrates clearly
a ferromagnetic-like transition with T ) 310-315 K (a
temperature step during the magnetization measurements was
K in this temperature range), and it has a large positive
Curie-Weiss temperature. (T will be estimated more precisely
below.) Bi Mn 10.5 shows clearly an antiferromagnetic transi-
tion with the Neel temperature, T , of 45 K, and it has a negative
Curie-Weiss temperature. The ZFC and FC curves of
Bi Mn 11.6 were almost constant below about 250 K, without
any additional anomalies at low temperatures (see the Supporting
Information) compared with Bi Mn 11, where features typical
for a re-entrant spin-glass were observed below 30 K. The
2
Mn -
Figure 4. Inverse magnetic susceptibilities of Bi
Bi Mn 11.6. The measurements were performed at 10 kOe between 2 and
00 K (filled symbols) and between 300 and 750 K (open symbols) using
3 3 3 3
Mn O10.5, Bi Mn O11, and
4
5+
O
11, and, for simplicity, Bi
3
Mn Mn
3
3
O
4
an oven attachment. The linear curves between 400 and 550 K depict the
3
3
O
3
3
O
Curie-Weiss fits, with the fitting parameters given in the figure. The arrows
C
3 3 3 3
demonstrate the preparation route of Bi Mn O10.5 from Bi Mn O11.6 inside
the oven during the measurements.
5
C
magnetic properties of Bi
netic behavior. Bi Mn O
3 3
3
Mn
11 is called a ferrimagnet because its
saturated magnetization reaches only a portion (3.19 µ at 5 K
), even though it
3
O11 are consistent with ferrimag-
2
3
3
3
O
N
B
2
3
and 50 kOe) of the maximum value (8 µ
B
3
3
O
has a positive Curie-Weiss temperature of 217 K. The
Curie-Weiss temperature is actually a sum of different interac-
tions between magnetic ions. In most cases, a positive
Curie-Weiss temperature corresponds to ferromagnets, and a
3
3
O
2
3
J. AM. CHEM. SOC. 9 VOL. 132, NO. 35, 2010 12429

A R T I C L E S
Belik and Takayama-Muromachi
Figure 6. Isothermal magnetization curves for Bi
3 3
Mn O11.6 at 5, 100, 200,
3
00, and 350 K (circles) and for Bi Mn 10.5 at 5 K (triangles). Inset shows
3
3
O
Figure 5. Specific heat data for Bi
Oe (open symbols) and 70 kOe (filled symbols) plotted as C
3
Mn
3
O
10.5 and Bi
3
Mn
3
O
11.6 (inset) at 0
pieces of Bi
3 3
Mn O11.6 attached to magnetized tweezers at room temperature.
p
/T vs T. An
anomaly near 350 K is due to a sample holder.
negative Curie-Weiss temperature corresponds to antiferro-
magnets. However, there are exceptions. For example, LaMnO
3
is a classical (canted) antiferromagnet. However, it has a positive
Curie-Weiss temperature of 52 K because the intraplane
ferromagnetic interactions are much stronger than the interplane
2
7
antiferromagnetic interactions.
Weiss temperature of Bi Mn 11 reflects the fact that ferro-
magnetic-type interactions are dominant. It is also difficult to
consider Bi Mn 11 as a canted antiferromagnet because of its
The positive Curie-
3
3
O
3
3
O
positive Curie-Weiss temperature and large saturated magneti-
zation.
Figure 5 depicts specific heat data of Bi
3 3
Mn O10.5 and
Bi
3
Mn Mn 10.5 shows a strong anomaly near T ,
3
O
11.6. Bi
3
3
O
N
which is almost independent of a magnetic field. This behavior
is typical for antiferromagnets, and the data unambiguously
confirmed the onset of the long-range antiferromagnetic order
in Bi Mn O10.5. Bi Mn O11.6 has a weak anomaly near T , and
3 3 3 3 C
a magnetic field smears the transition to a high temperature
region, which is typical for ferromagnets. The specific heat
anomaly in Bi
ferromagnetic order. The magnitude of an anomaly near T
(or the amount of the released entropy) depends on many
3
Mn
3
O
11.6 confirms the onset of long-range
C
or
T
N
factors. The higher the temperature, the weaker the magnetic
anomalies because of an increased contribution from the lattice.
Competition between different interactions or frustration and
structural disorder also significantly suppress magnetic anoma-
lies near T
the weak magnetic anomaly at T
Bi Mn 11.6. Very weak magnetic anomalies at T
found in the specific heat of LaMnO3+δ
specific heat anomalies were observed in Bi
Isothermal magnetization curves (M vs H) are shown in
Figure 6. In Bi Mn 11.6 at 50 kOe, the magnetization reaches
.33 µ /f.u. at 5 K (the value being very close to the full
magnetization) and 3.51 µ /f.u. at 300 K. These results show
that Bi Mn 11.6 is a true ferromagnet. Bi Mn
a very soft ferromagnet with negligible remnant magnetization
0.08 µ /f.u. at 5 K) and coercive field similar to those of
ferrimagnetic metal Sr and ferromagnetic semicon-
C
or T
N
. The above reasons may be responsible for
in the specific heat of
were also
We note that no
C
3
3
O
C
2
8
.
2
3
2
Mn
3
O
11
.
Figure 7. (a) Arrott plots (M vs H/M) for Bi
3
Mn
3
O
11.6 from 270 to 350
0
; circles) versus
3
-1
K with a step of 2 K. (b) Inverse initial susceptibilities (ꢀ
temperature for Bi Mn 11.6. The line shows the fitting results, with the
equation and fitting parameters given in the figure.
3
3
O
3
3
O
7
B
B
and magnetized objects at room temperature (see the inset of
Figure 6). At 350 K, an almost linear behavior was observed
on the M vs H curves of Bi
3
3
O
3
3
O11.6 behaves as
3 3
Mn O11.6. In antiferromagnetic
(
B
2
9
Bi Mn O10.5, linear M vs H curves were found at 5 K without
3
3
2
FeMoO
Mn 11.6 is attached to permanent magnets
6
30
any signs of hysteretic behavior.
To estimate T of Bi Mn 11.6 more precisely, we used the
Arrott plots (M vs H/M; Figure 7a). The Arrott plots deviate
from linear behavior near T , similar to some other ferromag-
nets. Therefore, we estimated the inverse initial susceptibilities
ductor BiMnO
3
.
Bi
3
3
O
C
3
3
O
2
(
(
27) Zhou, J.-S.; Goodenough, J. B. Phys. ReV. B 1999, 60, 15002.
28) Ghivelder, L.; Castillo, I. A.; Gusmao, M. A.; Alonso, J. A.; Cohen,
L. F. Phys. ReV. B 1999, 60, 12184.
C
31
(
29) Kobayashi, K. L.; Kimura, T.; Sawada, H.; Terakura, K.; Tokura, Y.
Nature 1998, 395, 677.
-
1
2
(ꢀ
0
) by smooth extrapolation of the M vs H/M curves above
1
2430 J. AM. CHEM. SOC. 9 VOL. 132, NO. 35, 2010

Effects of Oxygen Content on Properties of Bi
Mn O
3 3 11+δ
A R T I C L E S
ferromagnetic-type interactions and increase the strength of
interactions and, therefore, transition temperatures. Bi
3
Mn
3 11
O ,
with one-third of Mn5 ions, shows ferrimagnetic-like properties
+
2
3
and a transition temperature of about 150 K. The appearance
of spin-glass properties below 30 K in Bi Mn 11 gives support
for strong competition between antiferromagnetic and ferro-
magnetic interactions. Bi Mn 11.6, with about two-thirds of
3
3
O
3
3
O
5+
Mn , shows room-temperature ferromagnetism. Noticeable
changes of the magnetic transition temperature and magnetism
3 3
in Bi Mn O11+δ with δ can be compared with significant changes
of the magnetic and electronic properties of perovskite-like
1
7,18
19–21
LaMnO3+δ
and BiMnO3+δ
,
high-temperature copper
16
superconductors (e.g., YBa Cu
2
3
O
7+δ), and other cuprates (e.g.,
Cu(Re0.69Ca0.31)O6+δ). However, compared with perovskite-
type materials and cuprates, KSbO -type materials have been
investigated poorly, especially from the theoretical point of
32
Sr
2
3
1
2
17,18
19–21
Figure 8. Direct current resistivity data for Bi
3
Mn
3
O
10.5, Bi
3
Mn
3
O
11, and
view. In perovskites LaMnO3+δ
crystal symmetry changes with changing δ, in comparison with
Bi Mn 11(δ, where the cubic structure is stable over a wide δ
range. The structural stability of Bi Mn 11(δ can probably be
and BiMnO3+δ
,
the
3
3
3
Bi Mn O11.6. The data are plotted as F (in logarithmic scale) vs 10 /T. The
bold lines show temperature regions used for the estimation of the activation
energy.
3
3
O
3
3
O
-
1
explained by its channel-like feature (Figure 3): (additional)
oxygen atoms should be located in the channels, and they are
removed from the channels as confirmed by the structural
T
C
on the H/M axis. The ꢀ
0
vs T curve (Figure 7b) was fit by
31
-1
γ
the simple equation,
of T ) 307.0(2) K and γ ) 1.292(11).
.4. Transport Properties of Bi Mn
Mn 11.6. Figure 8 demonstrates that Bi
and Bi Mn 11.6 have semiconducting-type conductivity. The
activation energies in Bi Mn 11 (between 225 and 400 K) and
Bi Mn 11.6 (between 180 and 230 K) were almost the same
0.18 eV). This fact shows that these compounds behave as
narrow-band semiconductors. Bi Mn 11.6 shows a small change
of the activation energy above T . The activation energy in
Bi Mn 10.5 was about 0.31 eV. Bi Mn 11.6 should have
ꢀ
0
) A(T/T
C
- 1) , with the parameters
C
analysis of Bi
reflect the real changes in the composition. In perovskites, cation
are actually formed, even though the
3 3 3 3
Mn O10.5. The formula Bi Mn O11(δ seems to
3
3
3
O
3 3
10.5, Bi Mn O11, and
Bi
3
3
O
Mn O10.5, Bi Mn O ,
3 3 3 3 11
vacancies La1-xMn1-xO
3
3
3
O
formula is written as LaMnO3+δ for simplicity. Detailed
structural investigations and localization of additional oxygen
3
3
O
3
3
O
in Bi
differences among Bi
be seen from the available data. The formation of oxygen
vacancies in the channels of the Bi Mn 10.5 structure results
in increased disordering of Bi atoms in the channels: the Bi1
atoms are split by about 0.5 Å in Bi Mn
Bi Mn 11, and 0.25 Å in Bi Mn 11.6; the Bi2 atoms are split
by about 0.3 Å in Bi Mn 10.5 and show no splitting in
Bi Mn 11 and Bi Mn 11.6. The increased disordering of Bi
3
Mn
3
O11.6 are left for future work. Some structural
(
Mn Mn 11, and Bi Mn O11.6 can
3
O
10.5, Bi
3
3
O
3
3
3
3
O
3
C
3
O
3
3
O
3
3
O
3
additional oxygen atoms in the channel of the structure. Mobility
of oxygen atoms at higher temperatures may be responsible for
the change of the activation energy.
3
3
O10.5, 0.35 Å in
3
3
O
3
3
O
3
3
O
3
3
O
3
3
O
4
. Discussion
atoms can be explained by the fact that Bi atoms become
underbonded with the formation of oxygen vacancies. We note
Even though the target composition was Bi
resultant sample had the composition of Bi Mn O11.6. This fact
shows that 11.6 is the maximum oxygen content at the synthesis
conditions, and the structure cannot accommodate more oxygen.
The TGA data in hydrogen (see the Supporting Information)
3
Mn
3
O
12, the
3 3
that R
that those of Bi
and R
indexes in Bi
Mn
O
10.5 were significantly larger
3
O
B
F
3
3
2
3
3
Mn
3
O
11 and Bi
3
Mn 11.6 (Table 1). This fact
may indicate additional structural disorder, which cannot be
represented by the split-atom model.
and Ar (Figure 1) clearly confirmed that Bi
more oxygen than Bi Mn 11. We note that Bi
only be prepared from Bi Mn 11 or Bi Mn 11.6 by heating in
an inert atmosphere or in a vacuum. The direct high-pressure
high-temperature synthesis of Bi Mn 10.5 produced a sample
3
Mn
3
O11.6 contains
The origin of ferromagnetism in LaMnO
been investigated extensively using experimental and theoretical
approaches (the parent compound LaMnO is an antiferromag-
3
-based materials has
3
3
O
3
Mn
3
O
10.5 could
3
3
O
3
3
O
3
3+
netic insulator). The double-exchange mechanism between Mn
and Mn is capable of describing many experimental data on
these materials in the ferromagnetic metallic regime. However,
there exists ferromagnetic semiconducting phase in
3
3
O
4+
3
3
containing a lot of impurities (see the Supporting Information).
We should also emphasize step-like weight changes in
a
1
7,18
33
Bi
shows that other compositions with intermediate oxygen con-
tents can be stabilized, for example, Bi Mn
Oxygen content has a drastic effect on the magnetism of
3 3 3 3
Mn O11 and Bi Mn O11.6 on heating (Figure 1). This fact
LaMnO3+δ
,
La1-xCa
x
MnO
narrow δ and x ranges. For example, in LaMnO3+δ, semicon-
ducting ferromagnetic phases with T
≈ 200 K exist near δ ≈
.10. Some analogies can be seen in Bi Mn Mn
with Mn ions is an antiferromagnet, and Bi
3
,
x 3
and La1-xSr MnO in very
3
3 10.9
O .
C
0
3
3
O
11(δ: Bi
3
3 10.5
O
11.6 is a
Bi
Bi
4
3
Mn
Mn
3
O
O
11(δ and on the nature of magnetic interactions.
10.5, with the transition metal in one oxidation state of
+, has antiferromagnetic interactions between Mn ions and
a rather low T of 45 K. Note that Bi Mn 10.5 behaves as a
4+
3
Mn
3
O
4+
5+
3
3
semiconducting ferromagnet containing Mn and Mn ions.
4
+
If a metallic ferromagnetic phase exists in Bi
should appear for δ > 0.6, which could not be achieved in our
experiments. Magnetic and transport properties of LaMnO
3 3
Mn O11+δ, it
N
3
3
O
true antiferromagnet, that is, without any signs of spin canting.
3
-
Introduction of Mn5 ions into the system seems to produce
+
based materials strongly depend on Mn-O-Mn bond angles,
(
(
30) Kimura, T.; Kawamoto, S.; Yamada, I.; Azuma, M.; Takano, M.;
Tokura, Y. Phys. ReV. B 2003, 67, 180401.
(32) Isobe, M.; Kimoto, K.; Takayama-Muromachi, E. J. Magn. Magn.
Mater. 2007, 312, 91.
31) Kouvel, J. S.; Fisher, M. E. Phys. ReV. 1964, A136, 1626.
(33) Edwards, D. M. AdV. Phys. 2002, 51, 1259.
J. AM. CHEM. SOC. 9 VOL. 132, NO. 35, 2010 12431

A R T I C L E S
Belik and Takayama-Muromachi
4
4
38
which are 180° in the ideal perovskite structure with corner-
in K
2
Cr
8
O
16
,
and 33 K in CrBr
3
.
Before now, the highest
6 3 3
shared MnO octahedra. Bi Mn O11 has a different framework
Curie temperature for ferromagnetic insulators/semiconductors
2
4,45
made of edge- and corner-shared MnO
6
octahedra (Figure 3).
was reported for La
shows a new record high T
true ferromagnets. Insulating/semiconducting ferromagnets are
2
MnNiO
6
(T
C
≈ 280 K).
3 3 11.6
Bi Mn O
The Mn-O-Mn bond angles are about 100° and 130° in
C
among insulating/semiconducting
2
3
Bi
3
Mn
3
O
11
.
Therefore, it is difficult to apply classical rules
3
4,46
with 90° or 180° cation-anion-cation bridges (e.g.,
highly attractive materials for spin electronics.
In conclusion, we showed that the oxygen content in
Bi Mn O varies in a wide δ range, keeping the same cubic
Goodenough-Kanamori rules). It is interesting to note that
Bi
compounds Bi
been reported to have metallic-like conductivity.
Materials possessing ferromagnetic properties at room tem-
3 3
Mn O11(δ maintains semiconducting properties, while similar
3
3
11+δ
3
M
3
O
11 with 4d and 5d transition metals have
structure and semiconducting properties of the material. We
demonstrated for the first time that the oxygen content can vary
for the same cation composition in KSbO -type materials, and
the oxygen content can be increased further up to BiMnO3.867
(Bi Mn O11.6), meaning that there is additional space in the
7
–9,11
3
3
4-38
perature are of great practical interest.
They are used in
magnetic data storage, transformer cores, permanent magnets,
3
3
3
4
and so forth. Ferromagnetic dielectrics for spin polarization
and ferromagnetic diluted semiconductors
channels of the structure. We also discovered true ferromag-
netism in a semiconducting material, which is rather rare.
35,36
24,34,38
for spin electron-
ics have recently attracted much attention. Ferromagnetic-like
properties are observed in true ferromagnets (that is, where the
main interaction between magnetic ions is ferromagnetic), in
canted antiferromagnets or so-called weak ferromagnets, and
in ferrimagnets (where the main interaction between magnetic
ions is antiferromagnetic, and ferromagnetic-like properties
appear due to spin canting or uncompensated magnetic sublat-
Bi Mn O is a ferromagnet with the highest Curie temperature
3
3
11.6
(TC ) 307 K) for this class of materials (ferromagnetic
insulators/semiconductors). The Curie temperature of Bi Mn -
3
3
O11.6 is above room temperature, and which makes it very
important for practical applications.
Acknowledgment. This work was supported by World Premier
International Research Center Initiative (WPI Initiative, MEXT,
Japan), the NIMS Individual-Type Competitive Research Grant,
and the Japan Society for the Promotion of Science (JSPS) through
its “Funding Program for World-Leading Innovative R&D on
Science and Technology” (FIRST) Program. We thank Mr. K.
Kosuda of NIMS for electron probe microanalysis. The synchrotron
radiation experiments were performed at the SPring-8 with the
approval of the Japan Synchrotron Radiation Research Institute
3
8
tices). True ferromagnets usually have metallic conductivity,
for example, the elemental metals Fe (with magnetic transition
3
1
temperature T
C
) 1043 K), Ni (T
C
) 627 K), and Co (T )
C
3
8
38
17,18
1
388 K) and oxides CrO (T ) 386 K), SrRuO
2
C
3
(T
C
) 160
MnO
) 69
Antiferromagnets (including canted antiferromagnets and
3
9
K), LaMnO3+δ (δ ≈ 0.14, T
C
≈ 200 K),
La1-xSr
x
3
3
3
(
K).
x ≈ 0.3-0.5, T
C
≈ 350 K), and EuO (Eu-rich, T
C
3
8,40
ferrimagnets) are usually insulators or semiconductors. Insulat-
ing/semiconducting ferromagnets are always exceptions to the
general rule and, therefore, of interest not only from the practical
point of view but also from the viewpoint of the mechanism.
Many ferrimagnets and canted antiferromagnets have high
magnetic ordering temperatures well above room temperature,
(
Proposal Numbers 2009A1136 and 2010A1215). We thank Dr. J.
Kim and Dr. N. Tsuji for their assistance at SPring-8.
Supporting Information Available: Details of magnetization,
resistivity, laboratory and synchrotron XRD, TGA, and dielectric
measurements and bond lengths (PDF); X-ray crystallographic
data (CIF). This material is available free of charge via the
Internet at http://pubs.acs.org.
3
8
for example, magnetite Fe
ancient times, and perovskites Sr
Sr (T ) 440 K), BiCu
3 4 C
O (T ) 858 K), known since
29,37
2
FeMoO
6
(T
Mn
) 335 K). However, insulating
true ferromagnets with high T ’s are very rare. The typical
values of T are 100 K in BiMnO
C
≈ 450 K),
32
2
Cu(Re0.69Ca0.31)O
6
C
3
4 C
O12 (T
) 350
4
1
42
K), and Sr1-x
Y
x
CoO3+δ (T
C
JA1043598
C
3
0,43
C
1
3
,
∼200 K in LaMnO3+δ
(
42) (a) Kobayashi, W.; Ishiwata, S.; Terasaki, I.; Takano, M.; Grigoravi-
7,18
33
(
δ ≈ 0.10),
∼200 K in La1-xSr
x
MnO
3
(x ≈ 0.1), 180 K
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(
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