Fluorine insertion into the Ruddlesden-Popper phase La2BaFe 2O7: The structure and magnetic properties of La 2BaFe2O5F4

Article abstract of DOI:10.1039/c3dt52769g

Fluorination of the n = 2 Ruddlesden-Popper phase La₂BaFe ₂O₇ occurs at ～300 °C in flowing 10% F₂ in N₂ to form La₂BaFe₂O₅F ₄. This oxide fluoride contains 2F^- ions in interstitial sites within the rocksalt regions and 2F^- ions that have substituted for O^2- ions in apical sites within the rocksalt layers. The fluorination results in an expansion along c of 7.6% to yield a tetragonal unit cell of dimensions a = 3.96237(7) A, c = 22.3972(5) A. The structure and magnetic properties have been examined by Moessbauer spectroscopy, neutron powder diffraction and magnetic susceptibility measurements. La ₂BaFe₂O₅F₄ becomes antiferromagnetically ordered at temperatures below ～500 K, and the magnetic order shows a striking resemblance to that observed in La₂BaFe ₂O₇. The magnetic moments on Fe³⁺ are perpendicular to [001] and aligned along ±{100} directions above 300 K, but at temperatures below 200 K, they rotate by 45° to lie along ±{110}. Moessbauer spectroscopy suggests the presence of Fe ³⁺ within the primary phase, but also indicates that fluorination results in some particle fragmentation to form a paramagnetic component of the fluorinated material.

Full text of DOI:10.1039/c3dt52769g

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Fluorine insertion into the Ruddlesden–Popper
phase La BaFe O : the structure and magnetic
2
2 7
Cite this: Dalton Trans., 2014, 43,
2038
properties of La BaFe O F
2
2 5 4
a
a
b
a
Nicola N. M. Gurusinghe, Julia C. Fones, Jose F. Marco, Frank J. Berry and
Colin Greaves*
a
Fluorination of the n = 2 Ruddlesden–Popper phase La
2
BaFe
2
O
7
occurs at ∼300 °C in flowing 10% F
2
in
N
2
to form La BaFe
2
2 5 4
O F
. This oxide fluoride contains 2F− ions in interstitial sites within the rocksalt
regions and 2F− ions that have substituted for O2− ions in apical sites within the rocksalt layers. The fluori-
nation results in an expansion along c of 7.6% to yield a tetragonal unit cell of dimensions a = 3.96237(7)
Å, c = 22.3972(5) Å. The structure and magnetic properties have been examined by Mössbauer spectro-
2 2 5 4
scopy, neutron powder diffraction and magnetic susceptibility measurements. La BaFe O F becomes
antiferromagnetically ordered at temperatures below ∼500 K, and the magnetic order shows a striking
3
+
2 2 7
resemblance to that observed in La BaFe O . The magnetic moments on Fe are perpendicular to [001]
Received 4th October 2013,
Accepted 22nd November 2013
and aligned along ± ±100ꢀ directions above 300 K, but at temperatures below 200 K, they rotate by 45° to
3+
lie along ± ±110ꢀ. Mössbauer spectroscopy suggests the presence of Fe within the primary phase, but
DOI: 10.1039/c3dt52769g
also indicates that fluorination results in some particle fragmentation to form a paramagnetic component
of the fluorinated material.
www.rsc.org/dalton
which contains one interstitial fluoride ion located within alter-
nate rocksalt layers.
Introduction
7
The synthesis of metastable oxide fluorides via the low temp-
erature fluorination of layered inorganic oxides has received interest. For example, the paramagnetic Ru oxide Sr
significant attention since the discovery of superconductivity has been converted by oxidative insertion of fluoride ions to
The n = 2 Ruddlesden–Popper phases have also attracted
4
+
3
2 7
Ru O
1
5+
2 2 3 2 7 2
in the perovskite-related oxide Sr CuO F2+x. Subsequent fluor- form the Ru oxide fluoride Sr Ru O F , which exhibits
8
ination of perovskite-related oxides has demonstrated the canted antiferromagnetic behaviour below 185 K. We have
amenability of these structures to either substitution of oxide recently reported results of a study of the cationic order and
ions by fluoride ions, or to fluoride ion insertion into intersti- magnetic properties of the n = 2 Ruddlesden–Popper phase
2
–4
9
2 2 7
tial sites, especially in layered materials. These studies have La BaFe O , and we now report the product of its fluorination
led to modifications in both structural and physical properties. and its structural and magnetic characterisation.
For example, fluorination of the n = 1 Ruddlesden–Popper
4
phase LaSrMnO can result in the staged oxide fluoride
LaSrMnO F in which fluoride ions fully occupy the interstitial
4
5
,6
sites in alternate rock-salt layers. In this reaction, simple Experimental
fluorine insertion occurs in an alternating fashion, with conco-
mitant oxidation of Mn to Mn in the perovskite regions.
Where cations are more reluctant to oxidation, substitution reac-
tions (the replacement of one O ion by two F ions) can occur
with one of the fluoride ions occupying an interstitial position.
3+
4+
2 2 7
Samples of La BaFe O (100–200 mg), prepared as previously
described, were placed in a nickel boat and heated between
290 °C and 315 °C for 15 min in a flowing mixture of gaseous
9
2−
−
1
0% fluorine/90% nitrogen. X-ray powder diffraction (XRPD)
data were collected on a Bruker D8 diffractometer operating in
transmission geometry and utilising Cu-Kα radiation. Thermo-
2 4 2 3 2
In this way, the fluorination of Sr TiO can form Sr TiO F
1
gravimetric analysis (TG) was performed with a Netzsch
STA 449 instrument. The sample was heated at a rate of 10 °C
per minute in a gaseous mixture of 10% hydrogen/90% nitrogen
to 1100 °C. The products from fluorination were mixed
together to provide a suitably sized sample (ca. 2.5 g) for the
a
School of Chemistry, The University of Birmingham, Birmingham B15 2TT, UK.
E-mail: c.greaves@bham.ac.uk
b
Instituto de Quimica-Fisica “Rocasolano”, CSIC, Serrano 119, 28006 Madrid, Spain
2038 | Dalton Trans., 2014, 43, 2038–2043
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collection of neutron powder diffraction (NPD) data. The NPD
experiment was performed on diffractometer D2B at ILL, Gre-
noble, France; the wavelength was 1.5943 Å and the sample
was contained in a vanadium can (8 mm diameter). Refine-
ments in this report were based on high resolution data
obtained using only the central portion of the detector bank.
Structure refinements based on NPD and XRPD data were
1
0
performed using the GSAS programme and the EXPGUI
1
1
2−
−
interface. The site distribution of O
and F ions was
1
2
investigated using Madelung energy calculations.
5
7
The Fe Mossbauer spectra were recorded in constant
acceleration mode with a ca. 25 mCi Co/Rh source using a
helium closed-cycle cryorefrigerator. All the spectra were com-
puter fitted and the chemical isomer shift data are quoted rela-
tive to metallic iron at room temperature.
Magnetic susceptibility information was collected on a
Quantum Design MPMS SQUID magnetometer; data were
obtained on warming in a field of 500 Oe following cooling in
the same field (FC) or zero field (ZFC).
Results and discussion
TG analysis of the fluorinated La BaFe O resulted in a
2
2 7
product at 1100 °C which was shown by XRPD to be a mixture
of LaOF, BaF , Fe metal and a small amount of a perovskite
2
phase. We assume that the latter is barium-doped LaFeO3
which was present (1.9% by weight) in the starting oxide (vide
infra). The decomposition corresponds to:
3H2 þ La2BaFe2O5F4 ! 2LaOF þ BaF2 þ 2Fe þ 3H2O
After correction for perovskite impurity, the observed mass
loss (7.01%) compares well with a calculated loss of 7.03% for
the decomposition reaction above giving strong support for
2 2 5 4
the fluorinated product to have a composition La BaFe O F .
3
+
Surprisingly, this indicates no oxidation of the Fe , and
suggests a fluorination mechanism resulting in the replace-
5
7
Fig. 1
from La
Fe Mössbauer spectra recorded from La
2
BaFe
2
O
7
at 298 K and
BaFe at 298 K and 16 K. Data for La
2
O
5
F
4
2
BaFe O reprinted
2 7
ment of 2O by 4F− ions and hence the full occupancy of all
interstitial sites within the rocksalt regions of the structure.
XRPD structure refinements were performed in space group I4/
2−
2
from ref. 9 with permission from Elsevier.
9
4+
mmm for both phases; the results supported the occupancy of as shown by NPD data. The paramagnetic Fe component
interstitial sites in the rocksalt regions and indicated a sub- observed in the spectrum recorded at 298 K from La
stantial (7.6%) unit cell expansion along c, with a small expan- was associated with a barium-doped LaFeO impurity phase.
The Fe Mössbauer spectra recorded from La BaFe
298 K and 16 K are shown in Fig. 1 and the fit parameters are
The Fe Mössbauer spectrum recorded from La BaFe O at contained in Table 1. The spectrum recorded at 298 K showed
BaFe O
2
2 7
9
3
5
7
sion in the ab plane: La BaFe O
2 2 7
(a = 3.92308(4) Å, c = 20.8122(3)
2
2 5 4
O F at
Å), La BaFe (a = 3.96237(7) Å, c = 22.3972(5) Å).
2
2 5 4
O F
5
7
2
2 7
9
4+
2
98 K is shown in Fig. 1 and was best fitted to two sextets a minor (ca. 3%) singlet component characteristic of Fe but
with chemical isomer shifts δ = 0.36 mm s (characteristic of this component was absent in the spectrum recorded at 16 K.
Fe and accounting for ca. 97% of the spectral area) together We suggest that this singlet represents the barium-doped
−
1
3
+
−
1
9
with a singlet with chemical isomer shift δ = 0.10 mm s
LaFeO
characteristic of Fe and accounting for ca. 3% of the spectral from La
area). The two sextet patterns represent a distribution of mag- temperature and becomes incorporated within the dominant
3
impurity phase observed in the spectrum recorded
BaFe and which magnetically orders at lower
4
+
(
2
O
2 7
3
+
netic hyperfine fields reflecting the statistical probability of sextet patterns characteristic of Fe observed at 16 K. The
the distribution of lanthanum and barium around the FeO
major part (ca. 97%) of the spectrum recorded from La Ba-
at 298 K differs from its parent La BaFe phase in
6
2
octahedra which influences the positions of the oxygen atoms Fe
2
O
5
F
4
2
2 7
O
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5
7
Table 1
2 2 5 4
Fe Mössbauer parameters recorded from La BaFe O F
2
Temperature/
K
δ ± 0.02/
e qQ/2 ± 0.02/
mm s−
1
mm s
−1
H ± 0.5 T
Area ± 3%
2
98
0.10
3
25
44
28
6
0.26
0.39
0.38
0.74
−0.10
−0.09
0.88
42
38
16
0.46
0
0
.51
.48
−0.08
−0.09
55
53
44
49
3
+
the appearance of a significant (ca. 25%) paramagnetic Fe
component. The lower intensity of the paramagnetic doublet
at 16 K (ca. 6%) suggests that the fluorination process induces
a decrease in particle size which is represented by the para-
magnetic doublet observed at 298 K. At lower temperatures,
Fig. 3 Low angle NPD data from La
magnetic peaks (2θ ∼ 18° and 2θ ∼ 20°) at 300 K, and the change in rela-
tive intensity of these peaks between 300 K and 200 K.
2
BaFe
2
O
5
F
4
showing appearance of
2 2 5 4
the small particle La BaFe O F would be expected to magneti-
3
+
cally order and give a smaller paramagnetic Fe doublet in the
Mössbauer spectrum. This is confirmed in the spectrum
recorded at 16 K (Fig. 1) where the paramagnetic doublet
decreases in magnitude to ca. 6% and the two sextet patterns,
reflecting the distribution of lanthanum and barium around
noted that the almost identical neutron scattering lengths for
O (5.80 × 10− m) and F (5.65 × 10
15
−15
m) make it impossible
the FeO
6
octahedra, account for ca. 94% of the spectral area.
to determine directly the distribution of oxygen and fluorine
on the anion sites. At 300 K, the NPD pattern revealed strong
peaks that were inconsistent with the nuclear structure and
were attributed to magnetic scattering from a unit cell for
5
7
Importantly, the Fe Mössbauer spectra recorded from La Ba-
2
3
+
Fe
2
O
5
F
4
show that all the iron is present as Fe and that fluor-
BaFe is achieved without oxidation of iron.
ination of La
2
2 7
O
Magnetic susceptibility data are shown in Fig. 2. Although
the Mössbauer data indicated magnetic order below 298 K, the
magnetic susceptibility shows a general increase with decreas-
ing temperature, characteristic of a paramagnetic component.
A transition is observed at ca. 40 K at which point a deviation
occurs between the FC and ZFC data. The data are suggestive
of either a spin-glass transition or a canted antiferromagnetic
transition superimposed on a paramagnetic background.
Variable temperature NPD data were collected in order to
which a
m
= b
m
= √2a (the subscript m refers to the magnetic
cell). These peaks disappeared only at 500 K (Fig. 3), and the
data at this temperature were used for the initial structure
refinement. This confirmed the overall composition to be
La
2 2 9
BaFe (O/F) , in accordance with the Mössbauer and TG
data, which suggested the specific composition La BaFe O F .
Fig. 3 shows that the magnetic reflections at 2θ ∼ 18° and 2θ ∼
2
2 5 4
20° undergo a significant change in relative intensity between
200 K and 300 K, but no further change occurred at lower
provide a definitive structure for La BaFe O F and to probe
further the nature of its magnetic properties. It should be
2
2
5
4
temperatures. The change in relative intensities of the mag-
netic peaks is very similar to that observed in La BaFe , for
which a rotation of the magnetic moments occurs: above
200 K the moments are aligned along ± ±100ꢀ directions but
at lower temperatures they rotate 45° to point along ± ±110ꢀ
2
2 7
O
∼
1
3,14
directions.
Full Rietveld structural analyses were therefore
performed on 5 K and 300 K NPD data to provide complete
structural and magnetic details.
The final structural parameters resulting from the refine-
ments are given in Table 2, and some experimental details are
provided in Table 3. The Rietveld diffraction profiles for the
3
00 K and 5 K data are shown in Fig. 4. Because of the low
temperature fluorination, some minor contamination of the
product occurs (e.g. a (La, Ba)FeO perovskite, LaF , starting
3
3
oxide) and these inevitably are reflected in minor deviations in
the difference plots (Fig. 4). However, the inclusion of
additional phases into the refinements did not result in sig-
nificant improvements, given the additional variables intro-
duced. On the basis of Madelung calculations (vide infra), the
F atoms have a strong preference for the interstitial sites (F1)
and the apical sites on the edges of the perovskite blocks (F2),
Fig. 2 Variation of magnetic susceptibility of La
temperature.
2
BaFe
2
O
5
F
4
with
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Table 2 Refined structural data from NPD data at room temperature
and 5 K (italics)
Site
occupancy
iso
U ×
2
Atom
Site
x
y
z
100/Å
La/Ba1 2b
La/Ba2 4e
0
0
0
0
0
0.5
0.39(3)/0.61(3) 1.35(7)
.45(3)/0.55(3) 1.36(7)
0.3241(2) 0.81(1)/0.19(2) 1.35(7)
.3238(2) 0.78(2)/0.22(2) 1.36(7)
0
0
0
Fe
4e
2a
8g
4d
0
0.0863(2)
1
1
1
1
0.51(6)
0.02(6)
3.5(2)
0.0865(1)
O1
O2
F1
F2
0
0
1.8(2)
0
0.5 0.0969(2)
.0960(2)
0.25
2.09(8)
1.68(7)
3.2(2)
0
0.5
0
0
3.0(1)
16n 0.083(3)
.091(2)
0.8240(4) 0.25
0.8257(3)
2.7(4)
0.7(2)
0
I4/mmm; a = 3.9772(1) (3.9594(1)) Å, c = 22.281(1) (22.379(1)) Å, Rwp
.075(0.074), R = 0.058(0.057). Magnetic moment: 2.1(1)μ along ±100ꢀ
3.03(5)μ along ±110ꢀ).
=
0
p
B
(
B
Table 3 Details relating to the Rietveld refinements
Site occupancies
The F2 (apical) position is shifted from the
ideal position (0, 0, z) so that each site is split to
provide 4 closely spaced positions.
The La and Ba occupancies are constrained to
provide the correct composition but allow the
ions to distribute unevenly between La/Ba1
(
12-coordinate) and La/Ba2 (9-coordinate).
Fig. 4 NPD profiles for La
2
BaFe
2
O
5
F
4
after Rietveld refinement: (a)
Isotropic
displacements
Background
Uiso values were constrained to be equal for all
La and Ba ions.
This was modelled using a Shifted Chebyschev
function.
300 K and (b) 5 K [red (observed), green (calculated), mauve (difference)].
Black markers indicate nuclear reflections and red magnetic (in the P1
space group).
Magnetic
refinement
The NPD data were analysed using a separate
magnetic phase with P1 symmetry to allow full
flexibility to model the structure. The unit cell
dimensions were constrained to correspond
with the crystallographic unit cell.
symmetry nuclear structure with a separate magnetic phase
that allowed flexible orientation of the moment.
2 2 7
As has been observed for La BaFe O , the magnetic
which are closest to F1. This distribution is consistent with the moments at 300 K are directed along ± ±100ꢀ directions but
−
ions substituting for O2− ions at the closest positions, and have rotated to ± ±110ꢀ directions at 5 K. Fig. 3 shows that the
F
2
−
thereby facilitating egress of the replaced O
ions. The re-orientation occurs between 200 K and 300 K (the relative
barium ions are located preferentially in the larger 12-coordi- intensities of the magnetic peaks are very similar at 200 K and
nate sites within the perovskite block (La/Ba1) rather than the 5 K). Although we would expect the magnetic moment from
3
+
B
smaller, 9-coordinate sites in the rocksalt layers (La/Ba2). This NPD data to be significantly lower than the ideal 5μ for Fe
is exactly as was found in the precursor oxide and is expected, because of covalence and low dimensionality effects, the mag-
since cation rearrangement is unlikely to be significant at the netic moment at 5 K is much smaller than that in the oxide:
fluorination temperature.
The refinement of magnetic moment and magnetic order 300 K were found to be 2.57(5)μ
were achieved using a second, purely magnetic phase with low The low moment is a little surprising but may relate to a weak-
P1) symmetry to allow flexibility of the direction of the ening of magnetic exchange along [001] resulting from the sig-
3.03(5)μ
B
cf. 3.92(4)μ
B
(at 2 K). The moments at 200 K and
and 2.1(1)μ , respectively.
B
B
(
moment. The unit cell dimensions of this magnetic phase nificant expansion across the rocksalt regions. The overall
were constrained to comply with the dimensions of the crystal and magnetic structures at 300 K and 5 K are shown in
nuclear phase. This procedure is fairly standard, although Fig. 5.
refinements were also performed using single unit cells with
As is usual in oxide fluoride systems of the type studied
1
5
lower symmetries that were compatible with the magnetic here, bond valence sum calculations were not useful for dis-
2
−
−
structures at 5 K and 300 K. However, the results indicated crimination between possible distributions of the O and F
no significant structural distortion or improvement to the ions. For example, assuming the interstitial sites to be occu-
−
3+
fitting statistics. We therefore preferred to maintain the high pied by F , there are three possible sites bonded to Fe that
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that forms part of the rocksalt layers. This distribution has
4
−1
a Madelung energy of 3.24 × 10 kJ mol , 5% higher than
that of the next most stable anion distribution. These
results provide unequivocal evidence that the fluoride ions in
La BaFe O F are located in the two adjacent rocksalt layers
2
2 5 4
and the interstitial sites between them, as indicated in Table 2
and Fig. 5.
The main changes in cation coordination that occur upon
2 2 7
fluorination of La BaFe O are shown in Fig. 6. The site pri-
marily occupied by La in the oxide increases its coordination
3
+
to 12 in an arrangement very similar to that found for La
ions in the perovskite structure. Because of the negative charge
−
2 2 5 4
on the interstitial sites in La BaFe O F , the apical F anions
are repelled to provide a 12% decrease in its bond distance to
Fe. The equatorial Fe–O bonds are slightly expanded in the
oxide fluoride phase, which is consistent with the small expan-
sion of the unit cell edge length from 3.92308(4) Å to 3.96237(7)
Fig. 5 Structure of La
netic moments at (a) 300 K and (b) 5 K. Site assignments: blue (mainly
Ba), green (mainly La), yellow (F), red (O), black (Fe).
2
BaFe
2
O
5
F
4
showing the direction of the mag- Å (based on XRPD data).
The Mössbauer and NPD data clearly show that
La BaFe O F is antiferromagnetically ordered between 5 K
2
2 5 4
and 300 K. The magnetic susceptibility data (Fig. 2) therefore
−
could be occupied by F . All of these models gave a bond show some unexpected features that are worthy of comment.
valence sum in the range 3.07–3.10. The location of the fluor- The paramagnetic behaviour is probably due to a component
ide ions within the structure was therefore investigated using that has very small particle size, as was implied by Mössbauer
Madelung energy calculations to probe the electrostatic prefer- spectroscopy (vide supra). The magnetic feature at ∼40 K,
ences for various ion distributions. For a model involving a appears to be caused by the main phase La
random distribution of O/F over all anions sites, the sites although we cannot dismiss the possibility of a very small
labelled F1 and F2 in Table 2 have electrostatic potentials sub- amount of a ferromagnetic impurity. The oxide La BaFe
stantially lower than the other two anion sites (labelled O1 and does not give such a transition, and we are unaware of such a
O2). In fact, the interstitial site in the rocksalt region (F1) has transition being reported for the perovskite La1−xBa
a slightly negative potential. This confirms a very strong prefer- which we often see as an impurity during the synthesis of
ence of fluorine for the interstitial sites in accordance with La BaFe . We have shown that the same susceptibility data
expectation and previous results from similar reactions. were obtained from two samples of La BaFe , obtained
BaFe O F ,
2
2 5 4
2
2 7
O
x
FeO3−y,
O
2 7
2
2
2 5 4
O F
Further calculations were performed with fluorine located on totally independently, and the transition could possible imply
F1, and other possible distributions on the other anion posi- the occurrence of a canted ground state for the principal phase
tions. This revealed a very strong preference for all the remain- at this temperature. Analysis of NPD data either side of this
ing fluorine to be located only on the apical anion site (F2) temperature (at 30 K and 80 K) revealed no change in the
2 2 7 2 2 5 4
Fig. 6 Bond distances and coordination around Fe and site La/Ba2 (mainly La) in (a) La BaFe O and (b) La BaFe O F .
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magnetic order, but this is normal for canted structures where Characterising Next Generation Advanced Materials (West Mid-
the canting angle is small. lands Centre for Advanced Materials Project 1), with support
Given the significant structural change that occurs on fluor- from Advantage West Midlands (AWM) and part funded by the
ination of La BaFe , it is somewhat surprising that the same European Regional Development Fund (ERDF). Financial
reorientation of the magnetic moments occurs in La Ba- support from the Spanish Ministry of Science and Technology
2
2 7
O
2
9
,13,14
Fe
2
O
5
F
4
as has been previously reported in La
2
BaFe
2
O
7
.
It through project MAT2012-38045-C04-01 is also acknowledged.
suggests that the dominant 180° exchange interactions within
the perovskite layers are entirely accountable for this tran-
sition; otherwise the large expansion of the rocksalt region by
accommodation of the interstitial fluoride ions would be
expected to have a significant effect.
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1
2
3
4
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448.
We report the results of fluorine insertion into the n = 2
Ruddlesden–Popper phase La
2 2 7
BaFe O . Unlike similar phases
containing manganese, the fluorination occurs with no
3
+
oxidation of the Fe species, which is indicative of the higher
5
3+
3+
5 L. D. Aikens and C. Greaves, Chem. Commun., 2000, 2129.
reluctance of the d ion (Fe ) to oxidation compared to Mn .
The fluorination results in the formation of La BaFe O F with
6
7
8
9
L. D. Aikens, L. J. Gillie, R. K. Li and C. Greaves, J. Mater.
Chem., 2002, 12, 264.
P. R. Slater and P. K. B. Gover, J. Mater. Chem., 2002, 12,
2
2 5 4
−
two F ions in interstitial sites and two which have substituted
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cation site, predominantly occupied by La in La BaFe O ,
2
91.
R. K. Li and C. Greaves, Phys. Rev. B: Condens. Matter, 2000,
2, 3811.
2
2 7
becomes 12-coordinate in La
2
BaFe
2
O
5
F
4
. La
2
BaFe
2
O
5
F
4
is anti-
6
ferromagnetic with a Néel temperature ∼500 K. The ordered
structure has moments directed along ± ±100ꢀ directions above
N. N. M. Gurusinghe, J. de la Figuera, J. F. Marco,
M. F. Thomas, F. J. Berry and C. Greaves, Mater. Res. Bull.,
3
00 K, but at temperatures below 200 K, reorientation results
2013, 48, 3537.
in an alignment along ± ±110ꢀ. This rotation through 45° is
similar to that observed in La BaFe O .
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Acknowledgements
We are grateful to Emma Suard for assistance with the collec- 12 J. W. Weenk and H. A. Harwig, J. Phys. Chem. Solids, 1977,
tion of NPD data and acknowledge the provision of financial 38, 1047.
support for NPD facilities by the UK Engineering and Physical 13 D. Samaras and R. Chevalier, J. Magn. Magn. Mater., 1977,
Sciences Research Council. NNMG is grateful for the provision 5, 35.
of a research scholarship from the University of Birmingham. 14 D. Samaras and A. Collomb, Solid State Commun., 1975, 16,
The Bruker D8 diffractometer and the Netzsch STA 1279.
49 F1 Jupiter TG instrument used in this research were 15 I. D. Brown and D. Altermatt, Acta Crystallogr., Sect. B:
4
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