Synthesis and magnetic properties of a new layered oxide La 1.5Sr1.5Mn1.25Ni0.75O6.67

Article abstract of DOI:10.1134/S0036023610020178

A new oxide phase La_{1. 5}Sr_{1. 5}Mn _{1. 25}Ni_0.75O_{6. 67 ± 0 05}, a member of the A_n+1B_nO_{3n +1} (n = 2) Raddlesden-Popper homologue series, was synthesized, and its structure and magnetic properties characterized. Magnetic anomalies associated with the competition between antiferromagnetic and ferromagnetic orders are observed in the range of the temperatures studied (2-400 K). The ESR spectra of the compound feature the constriction of a magnetic signal and a shift toward g(Mn⁴⁺). Pleiades Publishing, Ltd., 2010.

Full text of DOI:10.1134/S0036023610020178

ISSN 0036ꢀ0236, Russian Journal of Inorganic Chemistry, 2010, Vol. 55, No. 2, pp. 247–253. © Pleiades Publishing, Ltd., 2010.
Original Russian Text © T.I. Chupakhina, G.V. Bazuev, E.V. Zabolotskaya, 2010, published in Zhurnal Neorganicheskoi Khimii, 2010, Vol. 55, No. 2, pp. 251–258.
PHYSICAL METHODS OF INVESTIGATION
Synthesis and Magnetic Properties of a New Layered Oxide
La1.5Sr1.5Mn1.25Ni0.75O6.67
T. I. Chupakhina, G. V. Bazuev, and E. V. Zabolotskaya
Institute of Solid State Chemistry, Ural Division, Russian Academy of Sciences,
ul. Pervomaiskaya 91, Yekaterinburg, 620219 Russia
Received May 5, 2008
Abstract—A new oxide phase La1.5Sr1.5Mn1.25Ni0.75O6.67 0.05, a member of the An + 1BnO3
(n = 2) Radꢀ
n
dlesden–Popper homologue series, was synthesized, and its structure and magnetic propertie+s c1haracterized.
Magnetic anomalies associated with the competition between antiferromagnetic and ferromagnetic orders
are observed in the range of the temperatures studied (2–400 K). The ESR spectra of the compound feature
the constriction of a magnetic signal and a shift toward g .
(Mn4+)
DOI: 10.1134/S0036023610020178
Complex oxide homologues of the An + 1BnO7 –
distribution to positions B was also established; the
δ
(n = 1, 2, 3) Raddlesden–Popper series have a perovsꢀ oxidation state (+4) was determined for manganese,
however, without specifying magnetic susceptibility as
a function of temperature [3].
kiteꢀlike structure and posses the entire set of properꢀ
ties intrinsic to the perovskite family. All members of
the series are built of perovskite blocks of cornerꢀsharꢀ
ing ВО6 octahedra, these blocks being infinite in plane
In turn, when magnetic and nonmagnetic cations
are ordered by the NaCl type in a perovskite unit layer
xy and having
n layers in direction z. Adjacent blocks
(
La2Sr2LiRuO8) but magnetic moments are randomly
are separated by rockꢀsalt blocks, so that the formula
unit may rightfully read [(ABO3)n(AО)]. Unlike classiꢀ
cal perovskite compounds, the layered phases in quesꢀ
tion have anisotropic physicochemical properties. Of
distributed between layers, there is Heisenberg antiferꢀ
romagnetism between layers [4]. In La3LiMnO7, Mn
cations inside each magnetic structural domain are
antiferromagnetically ordered when
Т < 14 K because
special interest are
n = 2 oxides, which have diverse
of the ordered lithium and manganese cation distribuꢀ
tion over positions B. Unlike in La2Sr2LiRuO8, howꢀ
ever, there is no longꢀrange magnetic order because of
the random distribution of magnetic moments along
properties, such as superconductivity, giant magnetic
resistance, and anionic conductivity. For example,
magnetic resistance found in Sr1.8La1.2Mn2O7 exceeds
200% in low magnetic fields of 0.3 T. This value is far
higher than in most manganeseꢀbased perovskites in
the same magnetic fields [1]. The results obtained on
manganites allow them to be recommended for use as
magnetic storage elements, pickups, oxygen memꢀ
branes, electrode materials, and catalysts.
axis с [5].
The more complex behavior in a magnetic field is
characteristic of compounds having two magnetic catꢀ
ions in positions B. For example, undoped manganites
may be antiferromagnets (as Sr3Mn2O7) [6] or demonꢀ
strate ferromagnetic properties at low temperatures
Wide possibilities for substitutions in both position
A and position B show a great potential for diverse
applications. Raddlesden–Popper manganites substiꢀ
tuted in position B are also of interest as model objects
for studying the interactions of two magnetic sublatꢀ
(
La2 – 2xSr1 + 2xMn2O7, where x = 0.3, 0.4) [7]. The
magnetic properties of doped manganites are conꢀ
siderably affected by the doping level and the nature
of a second magnetic cation. There are data on the
behavior in a magnetic field for the following manꢀ
ganites: Sr3Mn2 – xFexO7 – [8], LaSr2MnFeO7 [9],
La1.2Sr1.8Mn2 – xMxO7 – (M = Co, Fe, Cr) [10, 11],
tices. An + 1(Mn,B
'
)nO3
(n = 2, 3) oxides where posiꢀ
tion A is occupied by ne+it1her a rarerꢀearth element, or
an alkalineꢀearth element, or their combination and
position B' is occupied by another metal cation, have
been studied extensively. A random partial substitution
of a diamagnetic cation for manganese in octahedral
positions of a perovskite layer is known to lead to the
disappearance of magnetic order at low temperatures.
In particular, Sr3ScMnO6,5 within the range 2–300 K
δ
δ
La1.4Sr1.6Mn1 – xCuxO6 + [12], Sr3MnRuO7 [13], and
δ
LaSr2MnCoO7 [14]. For low substitution levels of
cobalt and iron for manganese, a ferromagnetic order
is maintained; when the cobalt and iron percentages
are higher than 20 at %, there occurs a transition to
spinꢀglass and clusterꢀglass states [10]. In chromiumꢀ
and rutheniumꢀcontaining oxides, ferromagnetic order
has no magnetic anomalies and obeys the Curie–Weiss appears even for high substitution levels (40 at %). The
law until 150 K [2]. For Sr3MnTiO7, random cation antiferromagnetic order of Bꢀsubstituted strontium
247

248
CHUPAKHINA et al.
manganites also tends to frustration induced by a ranꢀ
dom cation distribution over positions B.
RESULTS AND DISCUSSION
Previous research [14, 20, 21] demonstrated that
the quotient of the charges of BB’ cations (В4+/В3+ or
В4+/В4+) is significant for directing the crystallization
Raddlesden–Popper complex oxides (n = 2) conꢀ
taining Mn and Ni in positions B have not been
described. The literature only concerns the structure
of an A3BB'O7 – into Raddlesden–Popper (
n
= 2)
δ
and magnetic properties of LnSrMn0.5Ni0.5O4 (n = 1)
structure (space group
I4/mmm). When the mean oxiꢀ
and double perovskite La2NiMnO6 – [15–17]. The
dation number of BB’ cations is lower than 3.5, the
oxidation number of the A cation should be increased
via substituting rareꢀearth for alkalineꢀearth cations in
order for proper oxides to be prepared. Inasmuch as
manganites are, as a rule, synthesized at rather high
temperatures (1300–1400°C), the preferred oxidation
state of B cations at this temperature should be taken
into account in developing synthesis processes. The
Mn4+/Ni2+ quotient characteristic of solidꢀphase synꢀ
thesis processes does not favor the stabilization of tetꢀ
ragonal oxide structures; therefore, the mean cation
oxidation number in position A should be increased by
substituting lanthanum for strontium or temperature
be lowered by using precursor technology. Composiꢀ
tions were calculated using the procedure proposed by
Sarjeant et al. [22] who regarded a phase with an
equivalent substitution in position B as a mean
between the endꢀmember compositions of unsubstiꢀ
tuted oxides.
δ
lack of data is possibly because Raddlesden–Popper
phases with
the synthesis of An + 1(B,B
doped oxides. In some cases, ans+am1 ple forms a phase
with = 1 (the sample is not a single phase) or crystalꢀ
n
= 2 are far from being always formed in
'
)nO3 = 2, 3) heteroꢀ
(n
n
lizes in a quasiꢀoneꢀdimensional structure [18, 19].
The crystallization direction depends on the mean
oxidation number of A and B cations, as well as on the
cation radius in the relevant coordination [20].
In this work, we report the synthesis, structural and
magnetic characteristics of La1.5Sr1.5Mn1.25Ni0.75O6.67
,
a new representative of the Raddlesden–Pop0p.0e5r
homologue series.
EXPERIMENTAL
Strontium and lanthanum nitrates (chemically
pure samples), after being analyzed for the metal, were
mixed in stoichiometric proportions and then disꢀ
solved in distilled water under gentle heating (~70–
90°С). In parallel, calculated weighed portions of
Mn2O3 and NiO were dissolved in dilute nitric acid
under boiling. After cooling, the solutions were comꢀ
bined, and citric acid was added to the reaction mixꢀ
ture in a small excess relative to the equivalent amount
required for converting nitrates to citrates. Following
this, the solutions were concentrated to a jelly at 100–
150°С. The resulting substance was stirred and
exposed at 400–500°С until a dry residue was formed
and the residue ignited in the selfꢀpropagating highꢀ
temperature mode. The residue was transferred to a
crucible, heated to 700°С, exposed for 3–4 h at this
temperature to remove organic components, then calꢀ
cined at 900–950°С, after which compacted under
3000 kg/cm2 and stepwise annealed with temperature
elevated in 100ꢀK steps. The final annealing was carꢀ
ried out at 1450C; the synthesis duration was 25 h.
Samples of the La1.5Sr1.5MnNiO7 –
and
La1.5Sr1.5Mn1.25Ni0.75O7 – asꢀbatch compositioδns were
synthesized using both δroutine ceramic technology
and the aforementioned citrate procedure. The Xꢀray
diffraction pattern of La1.5Sr1.5MnNiO7 – contains
δ
reflections from the target Raddlesden–Popper phase
(
n
= 2), an impurity K2NiF4ꢀtype phase (Raddlesden–
Popper structure, = 1), and likely, a perovskite solid
n
solution. Longꢀterm exposure at 1450°C does not
change the phase composition of the reaction mixture.
Apparently, the solidꢀphase process stops with the forꢀ
mation of the K2NiF4 phase admixed with the targeted
structure. The precursor synthesis, which involves the
homogenization of the reaction mixture and the forꢀ
mation of microparticles as a result of the selfꢀpropaꢀ
gating highꢀtemperature process, displaces equilibꢀ
rium toward the major phase, which appears under the
given conditions starting at about 1400°C. A singleꢀ
phase sample of composition La1.5Sr1.5Mn1.25Ni0.75O7 –
was prepared by the precursor synthesis where finaδl
annealing was carried out at 1450°C for 25 h.
Xꢀray diffraction was measured on DRONꢀUMꢀ1
using Cu
K radiation. FULLPROFꢀ2006 software was
Oxygen was determined by the reduction of the
sample in flowing hydrogen at 950°C for 5 h. Theoretꢀ
ically, the ultimate products of such a process are lanꢀ
thanum oxide and strontium oxide, metallic nickel,
and MnO. However, Millburn and Rosseinsky [15]
reported that, during the reduction of an oxide having
α
used in the fullꢀprofile Rietveld analysis of Xꢀray difꢀ
fraction patterns.
Magnetic measurements were carried out on an
MPMSꢀXLꢀ5 Quantum Design SQUID magnetomeꢀ
ter at 2–300 K in magnetic fields of 0.5 and 5.0 kOe
after samples were cooled in a magnetic field (FC
mode) or without field (ZFC mode).
a similar elemental composition, LaSrMn0.5Ni0.5O4 +
,
under similar conditions (950°C, 3 h), the reactioδn
does not go to an end. As an impurity, the ultimate
ESR spectra were recorded on a CMS 8400 specꢀ products may contain manganese sesquioxide and an
trometer in the Xꢀband range at 118–473 K. The temꢀ undecomposed K2NiF4ꢀtype oxide. Noteworthy, subꢀ
perature maintenance accuracy was 3 K.
stituted manganites where positions B contain Co or
RUSSIAN JOURNAL OF INORGANIC CHEMISTRY Vol. 55 No. 2 2010

SYNTHESIS AND MAGNETIC PROPERTIES
249
I
, pulses
2000
1600
1200
800
400
0
–400
10
20
30
40
50
60
70
, deg
2θ
Fig. 1. Simulated, measured, and difference Xꢀray diffraction patterns for La Sr Mn Ni
O
1.25 0.75 6.67 0.05
.
1.5 1.5
Cu are reduced to the ultimate products in 30–45 min. Ni cations over positions B and of oxygen vacancies
In view of this, we increased the exposure time in flowꢀ over positions O3 and O1, with positions O2 being
ing hydrogen to 5 h. Powder Xꢀray diffraction clearly completely occupied.
shows SrO, La2O3, metallic nickel, and MnO in the
reduction products. Apart from these products, there
The unit cell parameters of La1.5Sr1.5Mn1.25
Ni0.75O6.67 are as follows:
а = 0.3847(2) nm, с =
are lowꢀintensity (~6–7%) reflections from a poorly
crystallized phase, which we failed to identify. By the
above data, we determined that the sample had oxygen
2.0137(1) nm. Atomic coordinates and interatomic
distances are listed in Tables 1 and 2.
nonstoichiometry ( = 0.33); in view of the occurꢀ
δ
rence of a foreign phase in the products, however, error
in the oxygen index may be 0.05. Because the sample
was synthesized in a severe temperature schedule, the
existence of nickel with an oxidation number exceedꢀ
ing +2 is hardly expectable; thus, the mean oxidation
number of manganese in the compound is +3.47.
Figure 1 shows the Xꢀray diffraction pattern of
La1.5Sr1.5Mn1.25Ni0.75O6.67 after the Rietveld fullꢀprofile
analysis using FULLPROFꢀ2006 software.
Magnetic Properties
Figure 2 shows magnetic susceptibility curves for
La1.5Sr1.5Mn1.25Ni0.75O6.67 measured 0.5ꢀ and 5ꢀkOe
magnetic field. The curves do not allow a unique interꢀ
pretation of the magnetic interactions in the sample,
but we should mention that a magnetic order exists
starting at rather high temperatures. The Curie–Weiss
law does not hold even within 300–400 K; at 140 K in
the 0.5ꢀkOe field, the curve features a peak. The furꢀ
ther trend of the curves provides evidence in favor of
Most of the An + 1BnО3
Raddlesden–Popper
n
+ 1
phases crystallize in tetragonal system (space group
/mmm). When = 2, La and Sr ions are in two posiꢀ
I4
n
tions (La1, Sr1) and (La2, Sr2) and oxygen resides in
three positions (O1, O2, O3). For Ni and Mn cations,
either random distribution over octahedral positions
or NaClꢀtype ordering is possible. In cases where the
order exists over the entire crystal lattice, the symmeꢀ
try is lowered and space group changes; in cases of ranꢀ
dom distribution over B positions, space group
Table 1. Atomic coordinates in La1.5Sr1.5Mn1.25Ni0.75O6.67
Coordinate Position
x
y
z
(La,Sr)2
(La,Sr)2
(Ni,Mn)
O1
2b
2b
4e
8g
4e
2a
0
0
0
0
0
0
0
0.5
0
0.3164(2)
0
0
0
0
0.0983(5)
0.0935(11)
0.1982(14)
0
I
4
/mmm is maintained. Analysis of diffraction data for
La1.5Sr1.5Mn1.25Ni0.75O6.67 showed that the least final
values ( B = 11.6 f = 10.6 Rwp = 12.9) are observed
when there are equiprobable distributions of Mn and
O2
R
,
R
,
O3
RUSSIAN JOURNAL OF INORGANIC CHEMISTRY Vol. 55 No. 2 2010

250
CHUPAKHINA et al.
Table 2. Interatomic distances in La1.5Sr1.5Mn1.25Ni0.75O6.67
space group /mmm
segment in the paramagnetic region on magnetic susꢀ
ceptibility versus temperature curves until 400 K does
not allow the determination of exact values of magꢀ
netic constants and, thus, the calculation of magnetic
moments and oxidation numbers of B cations. Calcuꢀ
lations on the basis of experimental magnetic suscepꢀ
(
I
4
)
Bond
d, nm
(La,Sr)1–Ni(Mn)
(La,Sr)1–O1
(La,Sr)1–O3
(La,Sr)2–Ni(Mn)
(La,Sr)2–O1
(La,Sr)2–O2
Ni(Mn)–O1
0.3364(5)
0.2692(14)
0.2720(1)
0.3217(5)
0.2644(4)
0.2735(3)
0.1926(1)
0.2000(13)
0.1979(8)
tibility data within 350–400°C result in
μ
= 6.01 B.
μ
The theoretical magnetic moment calculated with
account for oxygen nonstoichiometry for the
La1.5Sr1.5MnIV0.59MnIII0.61NiII0.75O6.67 formula unit is
5.54 B. However, the difference between the theoretꢀ
μ
ical and experimentally determined values of the magꢀ
netic moments may arise not only from the small
extent of the linear portion of the magnetic susceptiꢀ
bility versus temperature curve but also from an addiꢀ
tional contribution of the orbital magnetic moment
Ni(Mn)–O2
Ni(Mn)–O3
of the Ni2+ cation to the overall
μ value. Hong et al.
the antiferromagnetic character of magnetic order, but
the positive value of the Weiss constant (+185.16 K)
signifies the occurrence of magnetic regions in the
paramagnetic phase.
[16] report average theoretical and experimentally
determined values of magnetic moments in
LnSrMn0.5Ni0.5O4. For any oxidation and spin ratios
between manganese and nickel, the theoretical magꢀ
netic moment calculated from spin states solely is
lower than the experimentally determined value.
The ZFC and FC curves diverge at rather high temꢀ
peratures (of about 100 K), and the ZFC curve at 20 K
features a second maximum. On the whole, there is
some similarity in the behavior of the nickelꢀsubstiꢀ
tuted complex oxide and cobaltꢀsubstituted one [14];
however, their highꢀtemperature transition points are
The ESR spectra of La1.5Sr1.5Mn1.25Ni0.75O6.67
recorded above 293 K are broad symmetrical Lorenꢀ
zian singlets with a constant
gꢀfactor of 2.03. Above we
demonstrated that this compound, including its oxyꢀ
different. The nonexistence of a rather extended linear gen nonstoichiometry, contains three magnetic ions:
χ
, cm3/mol
3
–1
1/χ
, (cm /mol)
50
40
30
20
10
0
a
5 kOe
0.4
0.2
0
b
a
б
50 100 150 200 250 300 350 400 450
, К
T
0.5 kOe
5 kOe
0
100
200
300
, К
T
Fig. 2. Magnetic susceptibility vs. temperature for La Sr Mn Ni
O
in magnetic fields of 0.5 and 5 kOe during
1.5 1.5
1.25 0.75 6.67 0.05
cooling in (а) FC and (b) ZFC modes. In the inset, 1/
χ
= f(T) in a range of 70–400 K.
RUSSIAN JOURNAL OF INORGANIC CHEMISTRY Vol. 55 No. 2 2010

SYNTHESIS AND MAGNETIC PROPERTIES
251
Δ
H, Gs
3500
g
2.12
3000
2500
2.10
2.08
2.06
2.04
2.02
2000
1500
1000
500
0
100
200
300
400
500
, К
T
100
150
200
250
300
350
400
450
500
, К
T
Fig. 3. ESR line width vs. temperature. In the inset, gꢀfactor vs. temperature.
Ni2+
Mn3+
(
d8 configuration), Mn4+
(
(
d3 configuration), and enhanced, this line will experience exchange narrowꢀ
ing. In the case where S1 S2 = 1/2, the average
1/2(g1 g2
, which was frequently observed for Cu2+
d4 configuration).
=
g =
+
)
Ions having d4 electronic configuration are rapidly
relaxing ions; ESR spectra from them are observable
only at temperatures near the liquid helium temperaꢀ
ture. At higher temperatures, the spectral line broadꢀ
ens until becoming unobservable [23]. In the temperꢀ
ature range we studied, the relaxation times of Mn3+
ions are so small that these ions do not influence the
surrounding magnetic ions and behave to them as a
diamagnet. The Ni2+ and Mn4+ ions in the octahedral
ions in various nonequivalent positions. In our case,
we are dealing with different types of magnetic ions
having different spins (S S
(Mn4+) = 3/2 > (Ni2+) = 1),
different energy level systems, and different relaxation
times (Mn4+ ions relax more slowly than Ni2+ ions).
Therefore, Mn4+ ions will make a greater contribution
to the overall line [26], and the
gꢀfactor for the conꢀ
tracted signal will shift toward
g
(Mn4+)
.
surrounding give rise to ESR spectra with gꢀfactors of
Figure 3 shows the ꢀfactor and line width Н as
functions of temperature. As temperature decreases
from 473 to 278 K, the ESR line remains symmetric
g
Δ
~2.10–2.14 and ~1.98–1.99, respectively [24]. Howꢀ
ever, the spectral line observed is not characteristic of
none of these ions. Line shape analysis showed that
this signal is fitted by a single Lorenzian, which comꢀ
pletely rules out a superposition of two lines having
and has a fixed
g = 2.03. The line width decreases
smoothly from 538 to 374 Gs. As temperature
decreases further, the line starts to broaden with a
rather strongly differing gꢀfactors.
noticeable increase in the curvature of the
Δ
Н(Т)
curve; at 118 K, reaches 3057 Gs and the gꢀfactor
Δ
Н
The ESR signal observed in this magnetoꢀconcenꢀ
trated compound may arise from the occurrence of
strong exchange interactions between ions in planes
containing Mn and Ni ions, leading to a signal conꢀ
traction effect [25]. Given that exchange interactions
are weak (exchange rates are low) and different types
of ions occur in the unit cell, the resonance spectrum
consists of separate resolved lines that have different
increases to 2.12. The line shape becomes asymmetriꢀ
cal; namely, the halfꢀwidth of the lowꢀfield wing
decreases on the background of the general line broadꢀ
ening, and its amplitude rises over the halfꢀwidth and
amplitude of the highꢀfield wing. These trends of the
line width and
La1.5Sr1.5Ni0.75Mn1.25O6.67 are similar to the
trends observed in ferromagnetic semiconductors
[27, 28]. In these compounds, line narrowing occurs
, lines are contracted to one line with an in the paramagnetic range of temperatures with a conꢀ
ꢀfactor. As the exchange is progressively stant value. In approach to the transition temperaꢀ
g
ꢀfactor as functions of temperature in
Δ
Н(Т)
and
g(Т)
g
ꢀfactors. As the exchange rate becomes higher, the
lines broaden and are drawn to each other. When
g1 g2
average
J
ӷ
(
+
)βH
g
g
RUSSIAN JOURNAL OF INORGANIC CHEMISTRY Vol. 55 No. 2 2010

252
CHUPAKHINA et al.
5
4
3
2
1
0
1000
2000
3000
4000
H, Gs
Fig. 4. Evolution of ESR spectra vs. temperature: (
1) T = 293 K, A = 1.00; (2) T = 158 K, A = 0.96; (3) T = 143 K, A = 0.72;
= 123 K, = 0.87; and ( = 118 K, = 0.95.
(4)
T
A
5)
T
A
ture Тc
of a local order; the line broadens to acquire a characꢀ
teristic anisotropy. After reaching Тc, the ꢀfactor and
width of this line are so great that it becomes virtually
unobservable.
,
g
ꢀfactor increases because of the appearance was actually unobserved, although the line continued
broadening. Within 140–118 K, again increases to
approach unity on the background of a relatively small
increase in ꢀfactors (to 2.12) and a quite determinable
, while the amplitude difference remains virtually
A
g
g
ΔН
Thus, presumably, strong exchange interactions
existing inside Mn–Ni planes are of the ferromagnetic
type. This fact is fully supported by the above results of
magnetic susceptibility versus temperature measureꢀ
unchanged. This may arise from the existence of a secꢀ
ond type of exchange interactions in the system,
namely, antiferromagnetic interactions. According to
Huber [29], in the case of antiferromagnetic exchange
in the region far from the antiferromagnetic order, the
line width decreases with temperature elevation folꢀ
lowing a hyperbolic law and tends to an asymptote at
high temperatures. The gꢀfactor increases within narꢀ
row bounds with temperature elevation because of
increasing total magnetization of the sample. From
ments, which imply that the Weiss constant
exceeds zero. Probably, there are exchange clusters in
the system where ion spins at > 278 K start to align
to one another. As temperature approaches 140
(a maximum is observed at the same temperaꢀ
Θ
(185.16 K)
Т
Т
≈
K
χ(Т)
ture), some anisotropy of the spectrum appear and are
further enhanced; we ascertained this anisotropy as
the ratio of the halfꢀwidth of a lowꢀfield wing (lfw) to
the halfꢀwidth of a highꢀfield wing (hfw) and as the
wing amplitude ratio.
our Н(Т) curve, if we move toward lower temperaꢀ
Δ
tures, it follows that the line width that arises from
antiferromagnetic interactions remains virtually
unchanged within 473–278 K. Within 140–118 K, the
line broadens both on account of antiferromagnetic
interactions and because of the appearance of a shortꢀ
range ferromagnetic order inside exchange clusters. At
140 K, inꢀcluster local ordering occurs. However, the
overall moments of the clusters remain disordered,
intercluster exchange interactions being antiferroꢀ
Figure 4 shows ESR spectra in the vicinity of
140 K. At = 173 K, the signal anisotropy
Нlfw Нhfw ; when = 143 K, the signal anisotropy
Т
А =
≈
Т
Δ
/Δ
≤
1
Т
decreases to 0.72 and the amplitude ratio increases
accordingly. In response to a further temperature
depression, one might expect an even greater decrease
in
A
and a dramatic downfield shift of the line, i.e., a
ꢀfactors. However, this effect magnetic.
considerable increase in
g
RUSSIAN JOURNAL OF INORGANIC CHEMISTRY Vol. 55 No. 2 2010

SYNTHESIS AND MAGNETIC PROPERTIES
253
8. S. Ghosh and P. Adler, J. Mater. Chem. 12 (3), 511
In summary, our magnetic susceptibility study of
complex oxide La1.5Sr1.5Mn1.25Ni0.75O6.67 and the ESR
spectra show the two types of magnetic interactions,
which may be explained by a local order of B (Mn/Ni)
(2002).
9. I. B. Sharma, S. K. Magotra, D. Singh, et al., J. Alloys
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d
MnIVꢀOꢀMnIV interactions are antiferromagnetic,
dens. Matter. 12, 1981 (2000).
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According to Anderson’s data, the M1–O–M2 atom
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sublattice in Raddlesden–Popper phases with n = 2 is
of the NaCl type, but given a local order, the Xꢀray difꢀ
fraction pattern is indexed in terms of space group
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I
4/mmm. In view of this, not only powder Xꢀray difꢀ 15. J. E. Millburn and M. J. Rosseinsky, J. Mater. Chem.
8
,
1413 (1998).
fraction but also neutron diffraction fails to detect this
order. For example, the difference between the oxidaꢀ
tion numbers of lithium and manganese cations in
La3LiMnO7 is sufficiently great (+3), but only 6Li
NMR spectroscopy managed to discover the local
order of these cations in positions B. The formation of
antiferromagnetic MnIVꢀOꢀMnIV clusters enhances the
appearance of a lowꢀtemperature antiferromagnetic
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netic and ferromagnetic clusters are formed, the
former enhancing the progressive deviation from the
Curie–Weiss law in approach to the Néeltemperature,
while the latter being capable of interacting with one
another by the antiferromagnetic scenario. Apart from
the competitive interactions of magnetic clusters, the
presence of Mn3+ ions in the highꢀspin state enhances
an additional frustration of magnetic moments beyond
ferromagnetic and antiferromagnetic clusters and is
responsible for the considerable divergence of the FC
and ZFC curves in the low temperature region.
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