Moessbauer spectroscopy and magnetic properties of Ba5Feiii3-xMii19-x (M = Fe, Cu)

Article abstract of DOI:10.1006/jssc.1996.0279

The Moessbauer spectra of three phases of the tetragonal solid solution Ba₅Fe^III_3-xM^II_xF _19-x (M = Fe, Cu) obtained by substitution of Fe³⁺ by M²⁺ ions, have been studied, as well as their magnetic properties. A mechanism of substitution of the Fe³⁺ cations is proposed according to the Moessbauer data. These compounds are paramagnetic until 4.2 K, with very weak antiferromagnetic interactions below 30-40 K.

Full text of DOI:10.1006/jssc.1996.0279

JOURNAL OF SOLID STATE CHEMISTRY 125, 159–164 (1996)
ARTICLE NO. 0279
M o¨ ssbauer Spectroscopy and Magnetic Properties of
III
II
Ba Fe M F
(M ؍ Fe, Cu)
5
3؊x
x 19؊x
1
Patrick Gredin, Ariel de Kozak, and Ang e´ lique Pierrard
Laboratoire de Cristallochimie du Solide, U.R.A. CNRS 1388, Universit e´ Pierre-et-Marie-Curie, Tour 54,
4
place Jussieu, 75252 Paris Cedex 05, France
and
Yvon Calage
Laboratoire des Fluorures, U.R.A. CNRS 449, et de Physique de l’Etat Condens e´ , U.R.A. CNRS 807,
Universit e´ du Maine, route de Laval, 72017 Le Mans Cedex, France
Received February 7, 1996; in revised form May 14, 1996; accepted May 16, 1996
III
II
Ba Fe Cu F . These compounds are also characterized
5
2
18
The M o¨ ssbauer spectra of three phases of the tetragonal solid by X-ray diffraction and the thermal variation of their
III
II
solution Ba
5
Fe3؊x
M
x
F
19؊x (M ؍ Fe, Cu) obtained by substitution magnetic susceptibilities is measured.
3
؉
2؉
of Fe by M ions, have been studied, as well as their magnetic
3؉
properties. A mechanism of substitution of the Fe cations is
proposed according to the M o¨ ssbauer data. These compounds
are paramagnetic until 4.2 K, with very weak antiferromagnetic
SYNTHESES
The binary fluorides used in this work were prepared in
the laboratory. To obtain iron(III) fluoride, first
FeF · 3H O is prepared in solution by reaction in a plati-
interactions below 30–40 K.
 1996 Academic Press, Inc.
3
2
num crucible between Fe(NO ) · 9H O (R. P. Normapur)
and an excess of fluorhydric acid at 40% (R. P. Normapur);
the liquid is evaporated at 60ЊC and the solid is then slowly
3
3
2
INTRODUCTION
Ba M F fluorides, all tetragonal, are disclosed in many
BaF –MF binary systems (M ϭ Cr, Fe, Ga, In, Al) (1–5).
5
3 19
dehydrated in 6 h into light green FeF under an anhydrous
3
2
3
hydrogen fluoride stream at 750ЊC.
These compounds are the lower limit of solid solutions
III
II
Iron(II) fluoride is prepared starting from FeCl · 4H O
2
2
formulated Ba M3
Ϫ
MЈ F
19Ϫ
x
with 0 Յ x Յ 1, obtained by
5
x
x
(
R. P. Normapur). The chloride is first dehydrated into
substitution of one third of the trivalent cations by bivalent
cations. So, the upper limit of these solid solutions must
FeCl under an anhydrous hydrogen chloride stream at
2
III
II
250ЊC in 3 h and then immediately fluorinated in the same
be formulated Ba M MЈ F . In a previous work (6), we
5
2
18
reactor into light beige FeF by anhydrous hydrogen fluo-
2
studied the ternary system BaF –ScF –CuF and particu-
2
3
2
ride at 650ЊC in 4 h.
larly the solid solution Ba Sc3Ϫ Cu F
19Ϫ
x
with 0 Յ x Յ 1.
5
x
x
The colorless copper fluoride CuF is prepared by reac-
2
We showed that the cell parameters do not follow Vegard’s
3
ϩ
2
ϩ
tion between its hydroxycarbonate (Merck, extra pure)
and anhydrous hydrogen fluoride at 500ЊC. It is slightly
hygroscopic, must be protected from moisture in a dessica-
tor, and used within 2 weeks.
law, implying that the substitution of Sc by Cu is or-
dered. This fact is corroborated by the apparition of super-
structure lines on the X-ray powder pattern of Ba Sc
CuF . We proposed a mechanism of substitution based
on the description of the crystal structures of Pb Fe F
5
2
18
The ternary and quaternary fluorides Ba Fe F and Ba
5
3
19
5
5
3 19
Fe MF (M ϭ Fe, Cu) are synthesized by solid state reac-
2
18
(
7), Sr Fe F (8), and Ba Cr CrF (9). In the present work,
5 3 19 5 2 18
tion at 790ЊC for 20 h, in sealed gold tubes, starting from
stoichiometric mixtures of the binary fluorides.
we give some new arguments in favor of our mechanism
hypothesis, by a M o¨ ssbauer spectroscopic study of the
III
II
III
II
three phases: Ba Fe Fe F18.8,
Ba Fe Fe F , and
5
2.8
0.2
5 2 18
X-RAY DIFFRACTION
1
The cell parameters (Table 1) are determined and re-
fined from X-ray powder diffraction data collected on a
To whom correspondence should be addresssed; e-mail: adk@ccr.jus-
sieu.fr
1
59
0022-4596/96 $18.00
Copyright  1996 by Academic Press, Inc.
All rights of reproduction in any form reserved.

160
GREDIN ET AL.
TABLE 1
TABLE 3
d Spacings (A) in Ba
III
II
˚
Refined Cell Parameters for Ba
5
Fe3؊x
M
x
F19؊x (M ؍ Fe, Cu)
5
2
Fe FeF18
˚
˚
Compound
a (A)
c (A)
Z
d
mes.
d
calc.
h k l
I/I
0
d
mes.
d
calc.
h k l
I/I
0
III
II
Ba
Ba
5
Fe2.8Fe0.2
F
18.8
a
a
F18.8 ϭ 14.664(1)
2 Ȃ aF18
ϭ 20.565(2)
c
c
F18.8 ϭ 7.686(1)
F18.8 ϫ 2 Ȃ cF18
ϭ 15.347(2)
F18.8 ϫ 2 Ȃ cF18
ϭ 15.429(2)
4
16
7.26
6.15
5.34
5.14
4.95
7.271
6.150
5.346
5.141
4.961
4.599
4.471
4.098
3.944
3.837
3.710
3.635
3.570
2 2 0
2 0 2
3 2 1
4 0 0
3 1 2
4 2 0
2 1 3
3 3 2
4 2 2
0 0 4
1 1 4
4 4 0
5 1 2
6
1
3
4
2
7
1
2
2
25
3
10
74
3.425
3.393
3.250
3.203
3.075
2.547
2.515
2.482
2.425
2.380
2.299
2.289
2.235
3.427
3.393
3.252
3.205
3.075
2.547
2.516
2.481
2.424
2.380
2.299
2.289
2.235
6 0 0
2 2 4
6 2 0
5 3 2
4 0 4
7 3 2
7 4 1
6 2 4
6 6 0
3 1 6
8 4 0
6 4 4
4 2 6
14
35
35
100
37
6
3
4
3
8
5
Fe
Fe
2
2
FeF18
F18.8
ϫ
͙
Ba
5
CuF18
a
F18.8
ϫ
͙
2 Ȃ aF18
c
16
ϭ 20.568(2)
4
4
4
3
3
3
.60
.46
.096
.941
.835
.705
1
7 cm vertical Philips PW 1050/25 diffractometer using a
copper anticathode (␭ ϭ 1.5418 A). The diffraction pat-
terns are analyzed by the program EVA 3.01 (SOCABIM) 3.633
which allows the deconvolution of the KͰ component and 3.568
˚
27
21
3
2
the determination of the peak positions. According to the
3
ϩ
M o¨ ssbauer results, a part of the Fe ions was reduced into
2
ϩ
Fe during the synthesis of Ba Fe F . So, the compound
5
3
19
III
This structural description of the ‘‘F19’’ and ‘‘F18’’ type
II
prepared must be formulated Ba Fe Fe F18.8. All these
3
ϩ
2
ϩ
5
2.8
0.2
compounds shows that the substitution of M by M in
Ba M F must be ordered. This fact is corroborated by
fluorides (Tables 2–4) are indexed in the tetragonal system,
using the crystal structure data of Ba Fe F (10) for
5
3 19
5
3 19
the apparition of superstructure lines on the X-ray powder
III
II
Ba Fe Fe F
and by isotypy with Ba Cr CrF (9) for
2
ϩ
2
ϩ
5
2.8
0.2 18.8
5
2
18
patterns of the Ba Fe MF compounds (M ϭ Fe , Cu )
(
5
2
18
the two other phases.
˚
for example: 3 2 1 at 5.34 A on the pattern of Ba
5
Fe FeF ), implying a larger cell compared with that of
2
18
DESCRIPTION OF THE STRUCTURE OF Ba
5
Fe
3
F
19 AND
3
ϩ
2
ϩ
Ba Fe F (10). The substitution of Fe by M takes place
5
3 19
OF THE Ba Cr CrF18-TYPE COMPOUNDS
5
2
in the first channels, i.e., in the dimers, and the centers
of the barium tetrahedra inserted in the second type of
channels are all occupied by independent fluorine ions for
The structures of Ba Fe F (10) and Ba Cr CrF (9)
5
3
19
5
2
18
have been described by Welsch and Babel. They are closely
related and based on three subnetworks (Table 5): isolated
‘‘F19’’ and only half of them for ‘‘F18’’.
[
MF ] octahedra which form two kinds of channels along
6
¨
III
II
MOSSBAUER SPECTROSCOPY OF Ba
5
Fe2.8Fe0.2
F18.8 AND
the c axis (Fig. 1). The first channels contain isolated dimers
M F ] (Fig. 2) and in the second channels are inserted
III
2
II
5
Ba Fe
M F18 (M ؍ Fe, Cu)
[
2
10
‘
‘independent’’ fluorine ions which form with barium ions
The M o¨ ssbauer spectra of samples containing 5 mg/cm2
of natural iron were recorded at 300, 77, and 4.2 K using
infinite chains of edge-sharing or vertex-sharing [FBa ] tet-
rahedra.
4
TABLE 4
TABLE 2
d Spacings (A) in Ba Fe2.8Fe0.2F
5 18.8
d Spacings ( A˚ ) in Ba Fe CuF
5
2
18
˚
III
II
d
mes.
d
calc.
h k l
I/I
0
d
mes.
d
calc.
h k l
I/I
0
d
mes.
d
calc.
h k l
I/I
0
d
mes.
d
calc.
h k l
I/I
0
7
5.14
4.97
4.60
.27
7.272
5.142
4.973
4.599
3.857
3.636
3.574
3.428
3.407
3.252
3.208
3.086
2.562
2.549
2 2 0
4 0 0
3 1 2
4 2 0
0 0 4
4 4 0
5 1 2
6 0 0
2 2 4
6 2 0
5 3 2
4 0 4
6 0 4
7 3 2
7
4
3
2.488
2.391
2.343
2.294
2.179
2.169
2.139
2.093
2.087
2.078
2.057
1.976
1.929
1.863
2.486
2.391
2.344
2.293
2.179
2.168
2.139
2.094
2.087
2.078
2.057
1.975
1.929
1.862
6 2 4
3 1 6
6 5 3
6 4 4
9 1 2
5 1 6
8 0 4
8 2 4
9 3 2
5 3 6
8 6 0
8 4 4
0 0 8
7 3 6
2
8
2
7
5
4
4
3
3
3
3
3
3
3
3
2
.31
.18
.98
.63
.841
.664
.593
.453
.402
.278
.226
.086
.876
7.332
5.184
4.989
4.637
3.843
3.666
3.595
3.456
3.404
3.279
3.228
3.087
2.876
2 0 0
2 2 0
2 1 1
3 1 0
0 0 2
4 0 0
3 2 1
3 3 0
2 0 2
4 2 0
4 1 1
2 2 2
5 1 0
4
4
3
2.567
2.515
2.444
2.386
2.319
2.303
2.195
2.168
2.149
2.104
2.079
2.062
1.949
2.567
2.515
2.444
2.386
2.319
2.303
2.195
2.168
2.149
2.104
2.079
2.062
1.949
5 2 1
5 3 0
6 0 0
2 1 3
6 2 0
5 1 2
5 4 1
3 2 3
4 4 2
5 3 2
4 1 3
6 0 2
7 2 1
6
2
9
10
15
19
9
20
2
34
47
18
3
8
23
11
19
3
18
29
41
20
2
6
3.854
3.635
3.574
3.428
3.406
3.251
3.208
3.084
2.562
2.549
34
15
56
16
49
45
100
66
2
40
18
55
13
53
50
100
55
2
18
2
3

III
II
PROPERTIES OF Ba
5
Fe
3
Ϫ
x
M
x
F
19
Ϫ
x
(M ϭ Fe, Cu)
161
TABLE 5
Comparison of the Three Subnetworks
in Ba
5
Fe
3
F
19 and Ba
5
Cr
2
CrF18
Subnetwork
Ba
5
Fe
3
F19 (I4/m)
5
Ba Cr
2
CrF18 (I4
1
/a)
Isolated [MIII
F
]3 octahedra (Fig. 1)
Ϫ
[
M
2
F
12
]
6
[
5
MF ]
Isolated dimers
Isolated dimers
III
4
Ϫ
II
6
Ϫ
[
Fe
two octahedra
Fig. 2a)
2
F
10
]
of
[Cr
2
F
10
]
of
octahedron ϩ prism
(Fig. 2b)
(
[
Ba
or
Ba
5
F
2
]
Infinite chains of
edge-sharing
Twisted chains of
vertex-sharing
[FBa ] tetrahedra
4
FIG. 1. (0 0 1) projection of the [M
2 5 3 19
F12] subnetwork in Ba Fe F
[
5
F]
[FBa
4
] tetrahedra
(
a) and Ba Cr CrF18 (b). 1 and 2 indicate the two kinds of channels.
5
2
quadrupolar splitting (Q.S.) (Table 6) are in agreement
with the usual observed values for iron(II) and iron(III)
six-coordinated in high-spin fluorides (11). Nevertheless,
the Lorentzian linewidths (⌫) are large, specially for the
iron(III) which exhibits a linewidth ⌫ double in comparison
with the natural one. This anomalous line broadening, al-
ready observed for other compounds with isolated iron
polyhedra, can be attributed to an electronic relaxation
effect (12).
III
II
Ba Fe Fe F
0.2 18.8
5
2.8
2 5 3 5 2
FIG. 2. [M F10] dimers in Ba Fe F19 (a) and Ba Cr CrF18 (b).
The spectra recorded at 300 and 77 K exhibit a well
resolved quadrupolar doublet and a single line of weak
a 57Co radioactive source diffused in a rhodium matrix. intensity (Fig. 3). This one is in agreement with a parasitic
The spectra recorded at 4.2 K are similar to those obtained iron(II) component (Ȃ 6% rate of the total iron at 300 K).
at 77 K: they are therefore not described hereafter.
At 4.2 K the compound is always paramagnetic despite a
The isomer shift relative to metallic iron (I.S.) and the strong broadening of the linewidth of the doublet which
TABLE 6
III
II
III
2
II
M o¨ ssbauer Data for Ba
5
Fe2.8Fe0.2
F18.8 and Ba
5
Fe
M F18 (M ؍ Fe, Cu)
FeIII
FeII
T
(K)
I.S.a
0.43
⌫
Q.S.
%
Ϯ 2
%
Fe
I.S.a
⌫
Q.S.
%
Ϯ 2
%
Fe
III
II
Compound
(mm/s) Ϯ 0.01
(mm/s) Ϯ 0.01
III
II
Ba
5
Fe2.8Fe0.2
F
18.8
300
0.40
0.40
0.42
0.42
0.35
0.67
0.40
0.85
67
27
71
20
0
.43
0.49
.49
94
91
1.09
1.66
0.32
0.36
2.23
2.40
6
9
6
7
7
0
9
Ba
5
Fe
2
CuF18
300
0.41
0.52
0.54
0.48
0.33
0.38
100
100
100
100
7
7
5
Ba Fe
2
FeF18
300
0.43
0.53
0.47
0.45
0.33
0.32
63
63
63
63
1.24
0.36
0.33
0.32
0.35
1.45
2.46
1.62
2.56
19
18
15
22
1
.23
1.39
.36
37
37
7
7
1
a
Isomer shift relative to metallic iron at 300 K.

162
GREDIN ET AL.
III
II
5 5 2 5 2
FIG. 3. M o¨ ssbauer spectra at 300 and 77 K for Ba Fe2.8Fe0.2F18.8, Ba Fe CuF18, and Ba Fe FeF18.
indicates a beginning of a tridimensional magnetic order. dra, with a local symmetry of the octahedron which leads
The Fe2 component is still in a paramagnetic state at this to a Q.S. value of 0.35 mm/s. Site 2 corresponds to the
ϩ
2
ϩ
2
ϩ
temperature, indicating that the Fe cations are well part isolated dimer and the 6% rate of Fe cations only takes
of the structure. So, the latter must be formulated place in the dimer: 27 ϩ 6 ϭ 33%.
III
II
Ba Fe3
Ϫ
Fe F
19Ϫ
x
with x ȁ 0.18. The theoretical distribu-
tion of the Fe cations in Ba Fe F (space group I4/m, Ba Fe Cu F
5
x
x
3
ϩ
III
II
5
3
19
5
2
18
No. 87 (10)) is 67% in the isolated octahedra (site 8h) and
3% in the isolated dimer (site 4e). The fitted results given
In this compound, isostructural with Ba Cr CrF (space
5
2
18
3
group I4 /a, No. 88 (9)), exist four potential independent
3
ϩ
1
in Table 6 indicate the presence of two Fe sites with, at
00 K,
crystallographic sites for iron(III): two independent and
3
quite regular octahedral sites in the [M F ] subnetwork
2
12
(
[
sites 16f ) and two distorted six-coordinated sites in the
M F ] dimer (sites 8e). On the M o¨ ssbauer spectra only
Site 1 Q.S. ϭ 0.35 mm/s P ϭ 67%
Site 2 Q.S. ϭ 0.67 mm/s P ϭ 27%.
2
10
3
ϩ
one single Fe component is observed, leading to a fitted
Q.S. value of 0.33 mm/s at 300 K (Fig. 3). In agree-
Site 1 corresponds to the isolated, quite regular, octahe- ment with the results observed for the Q.S. in

III
II
PROPERTIES OF Ba
5
Fe
3
Ϫ
x
M
x
F
19
Ϫ
x
(M ϭ Fe, Cu)
163
TABLE 7
Curie Constants C
M
II
and Paramagnetic Curie Temperatures
III
III
2
II
␪
p
5
for Ba Fe2.8Fe0.2
5
F18.8 and Ba Fe
M F18 (M ؍ Fe, Cu)
C
M(obs.)
C
M(th.)
␪
p
Ϫ
1
3
Ϫ
1
3
Compounds
(mol · cm · K)
(mol · cm · K)
(K)
III
II
Ba
5
Ba
5
Ba
5
Fe2.8Fe0.2
Fe
Fe
F
18.8
12.46
9.33
11.90
12.85
9.13
11.75
Ϫ6.7
ϩ1.9
ϩ0.3
2
2
CuF18
FeF18
␪p given in Table 7. The Curie constants are very close
to the theoretical ones calculated with the usual Curie
3
ϩ
2
ϩ
2
ϩ
constants for Fe and Cu and for the Fe cation with
a locked orbital moment. Below about 40 K, the decrease
FIG. 4. Thermal variation of the reciprocal molar susceptibilities for of ␹ · T may indicate weak antiferromagnetic interactions
III
II
III II
Ba
5
Fe2.8Fe0.2
F18.8 and Ba
5
Fe
2
M F18 (M ϭ Fe, Cu).
(Fig. 5). Nevertheless, the greatest care must be taken
for more precise interpretations, because ␪ values and
p
interactions are very weak. According to the structure of
these compounds, direct exchanges between transition ions
Ba Fe Fe F , the Fe3 ions may only occupy the regu- are impossible. However, indirect exchanges through one
III
II
ϩ
5
2.8
0.2 18.8
2
ϩ
Ϫ
3
ϩ
lar octahedral sites of the [M F ] subnetwork. The Cu
ions are then all localized in the dimer.
F ion between two transition ions, M in Ba Fe F and
5 3 19
ϩ ϩ ϩ
2
12
2
2
2
M
in Ba Fe MF (M ϭ Cu , Fe ), can occur in the
5 2 18
dimers, as well as weak long-range interactions through
F anions. In any case, the absence of a Zeeman sextet in
the M o¨ ssbauer spectra between 40 and 4.2 K rules out
Ϫ
III
II
Ba Fe Fe F
18
5
2
In this compound, isostructural with Ba Fe CuF , one the possibility of a 3-D cooperative extension of these
5
2
ϩ
2
18
single Fe3 component and two distinct Fe components interactions above 4.2 K. Only a line broadening is ob-
ϩ
are observed on the M o¨ ssbauer spectra (Fig. 3). The fitted served on the spectra, which confirms a beginning of a
3
ϩ
data lead to a Q.S. for the Fe cations of 0.33 mm/s, tridimensional magnetic order in agreement with the mag-
in agreement with a location of the latter in the regular netic measurements. The N e´ el temperature of all these
3
ϩ
octahedral sites of the [M F ] subnetwork. The Fe rate fluorides must be considerably lower than 4.2 K.
2
12
is near 2/3 of the total iron.
The remaining 1/3 of the total iron which corresponds
to the Fe2 ions is localized in the isolated dimers. The
local symmetries of the two sites of the dimer are not
CONCLUSION
ϩ
M o¨ ssbauer spectroscopy has demonstrated that the sub-
2
ϩ
3
ϩ
2
ϩ
2
ϩ
equivalent. This fact is well demonstrated by the Fe ions stitution of Fe by Fe or Cu cations in Ba Fe F to
5
3 19
which amplify the local symmetry effect (13), with two
very different values for the quadrupolar splitting. The
occupation rate of the two sites is equal (50/50), in
agreement with a dimeric entity.
III
II
MAGNETIC MEASUREMENTS ON Ba
5
Fe2.8Fe0.2
F18.8 AND
III
2
II
Ba
5
Fe
M F18 (M ؍ Fe, Cu)
Magnetic measurements were carried out between 4.2
and 300 K by the Faraday method with Hmax ϭ 10000 G.
The powder samples were inserted into an air-tight Teflon
container and diamagnetic corrections were applied. The
plots of the reciprocal molar susceptibility ␹M versus tem-
Ϫ
1
perature for the three compounds are displayed in Fig. 4.
Above 30–40 K, Curie–Weiss laws are well obeyed with
III
II
FIG. 5. Thermal variation of ␹ · T for Ba
5
Fe2.8Fe0.2F18.8 and
III II
Curie constants C and paramagnetic Curie temperatures Ba
5
Fe
2
M F18 (M ϭ Fe, Cu).
M

164
GREDIN ET AL.
III
II
3
4
. A. de Kozak and M. Samou e¨ l, Rev. Chim. Miner. 18, 255 (1981).
. M. Samou e¨ l, A. de Kozak, J. Renaudin, and G. Ferey, Z. Anorg.
Allg. Chem. 569, 169 (1989).
. A. de Kozak, M. Samou e¨ l, J. Renaudin, and G. Ferey, Z. Anorg.
Allg. Chem. 613, 98 (1992).
give Ba Fe3
Ϫ
M F
19Ϫ
is strictly ordered and only takes
x
5
x
x
place in the dimers. Therefore it is not possible to substitute
more than one third of the Fe3ϩ cations of the structure:
x is limited to the value 1. This limit is also observed for
5
5
3Ϫ
x
x
19Ϫ
x
the solid solution Ba Sc Cu F (6) and for all the other
6. P. Gredin, A. de Kozak, M. Quarton, J. Renaudin, and G. Ferey, Z.
Anorg. Allg. Chem. 619, 1088 (1993).
III
II
Ba M3
Ϫ
MЈ F
19Ϫ
x
solid solutions hitherto described (M ϭ
Cr, Fe, V, Ga; MЈ ϭ Ni, Mn, Cu, Fe) (1–3, 14–17).
The three compounds Ba Fe Fe F , Ba Fe Fe
5
x
x
7
. C. Jacoboni, A. Le Bail, R. de Pape, and J. P. Renard, Stud. Inorg.
Chem. 3, 687 (1993).
III
II
III
II
5
2.8
0.2 18.8
5
2
8. J. Graulich and D. Babel, Z. Anorg. Allg. Chem. 597, 51 (1991).
9. M. Welsch, H. Holler, and D. Babel, Z. Anorg. Allg. Chem. 575,
171 (1989).
0. M. Welsch, Thesis, Marburg/Lahn, Germany, 1991.
1. M. Leblanc, G. Ferey, Y. Calage, and R. de Pape, J. Solid State Chem.
III
II
F , and Ba Fe Cu F are paramagnetic until 4.2 K. How-
18
5
2
18
ever, weak and localized antiferromagnetic interactions
occur below 30–40 K. The broadening of the linewidth of
1
1
the Fe3 M o¨ ssbauer doublets in Ba Fe Fe F at 4.2 K
ϩ
III
II
5
2.8
0.2 18.8
5
3, 360 (1984).
indicates a beginning of a tridimensional magnetic order.
1
2. S. Morup and N. Thrane, Phys. Rev. B 8, 1020 (1984).
Some new measurements are in progress, especially to 13. Y. Calage and F. Varret, Chem. Phys. Lett. 55, 380 (1978).
1
1
4. A. de Kozak and M. Samou e¨ l, Rev. Chim. Miner. 15, 406 (1978).
5. M. Samou e¨ l, A. de Kozak, J. Renaudin, M. Leblanc, and G. Ferey,
Rev. Chim. Miner. 22, 64 (1985).
determine the N e´ el temperatures of these compounds.
REFERENCES
16. M. Samou e¨ l, A. de Kozak, J. Renaudin, and G. Ferey, J. Less-Com-
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1
2
. M. Samou e¨ l and A. de Kozak, Rev. Chim. Miner. 14, 471 (1977).
. M. Samou e¨ l and A. de Kozak, Rev. Chim. Miner. 15, 268 (1978).
17. M. Samou e¨ l, A. de Kozak, J. Renaudin, and G. Ferey, Z. Anorg.
Allg. Chem. 590, 200 (1990).