Magnetic properties of (Mn1-xVx)Sb2O4 with one-dimensional magnetic arrays

Article abstract of DOI:10.1002/1521-396X(200202)189:2<429::AID-PSSA429>3.0.CO;2-8

The magnetic properties of mangan-vanadium antimonate solid solution (Mn_1-xV_x)Sb₂O₄ (x = 0 to 0.6) with the tetragonal TX₂O₄ structure (T = Pb⁴⁺, Sn⁴⁺; X = Pb²⁺ or T = Mn²⁺, Fe²⁺, Co²⁺, Ni²⁺; X = Sb³⁺, As³⁺) were investigated. Magnetic measurements on the polycrystalline specimens have shown that characteristic ferromagnetic behavior appears in the case that x is larger than 0.1, whereas the final compound MnSb₂O₄ is an antiferromagnet with the Neel temperature T_N = 60.5 K. The magnetic isotherms of the solid solution at low temperatures show ferromagnetic jumps at low fields but do not tend to saturate up to 5 T. The zero-field cooling magnetic susceptibility has a maximum at T_c = 57 K, which is independent of both the vanadium concentration x and the frequencies of the applied external fields.

Full text of DOI:10.1002/1521-396X(200202)189:2<429::AID-PSSA429>3.0.CO;2-8

phys. stat. sol. (a) 189, No. 2, 429–432 (2002)
Magnetic Properties of (Mn V )Sb O
4
1
–x
x
2
with One-Dimensional Magnetic Arrays
1
H. Abe ) (a), K. Yoshii (b), and H. Kitazawa (a)
(
(
a) National Institute for Materials Science (NIMS), Tsukuba, Ibaraki 305, Japan
b) Japan Atomic EnergyResearch Institute (JAERI), Mikazuki, H yo go 679-5143, Japan
(
Received May 1, 2001; accepted September 30, 2001)
Subject classification: 75.50.Dd; S10.15
The magnetic properties of mangan-vanadium antimonate solid solution (Mn1 –– xVx)Sb2O4 (x = 0 to
4
+
4+
2+
2+
2+
2+
2+
0
.6) with the tetragonal TX2O4 structure (T = Pb , Sn ; X = Pb or T = Mn , Fe , Co , Ni ;
3+
3+
X = Sb , As ) were investigated. Magnetic measurements on the polycrystalline specimens have
shown that characteristic ferromagnetic behavior appears in the case that x is larger than 0.1,
whereas the final compound MnSb2O4 is an antiferromagnet with the Neel temperature
TN = 60.5 K. The magnetic isotherms of the solid solution at low temperatures show ferromagnetic
jumps at low fields but do not tend to saturate up to 5 T. The zero-field cooling magnetic suscept-
ibility has a maximum at Tc = 57K, which is independent of both the vanadium concentration x
and the frequencies of the applied external fields.
Introduction Ternary transition metal oxides represented by a general formula TX2O4
4
+
4+
2+
2+
2+
2+
2+
3+
3+
(
T = Pb , Sn ; X = Pb or T = Mn , Fe , Co , Ni ; X = Sb , As ) have been
investigated mainly from a viewpoint of structural chemistry [1–3]. The TX2O4 struc-
4+
2+
ture is derived directly from the tetragonal Pb3O4 (Pb Pb 2O4, P42/mbc) structure by
4
+
2+
substituting the Pb sites for T, and the Pb sites for X. This structure has a unique
characteristic as seen in Fig. 1: TO6 octahedra form one-dimensional {TO4}1 arrays
along the c-axis by sharing their ledges with each other, and the arrays are linked via
the tri-coordinated X ions. Such ledge-sharing arrays are identical to the {TiO2}1 arrays
in the Rutile structure. Moreover, several previous studies on the nature of the chemi-
cal bonds in TX2O4 have revealed that the X–O bonding is prominently covalent com-
pared to the T–O bonding [3]. This suggests that TX2O4 can be regarded as a Rutile
system “diluted” by non-magnetic (XO) units with high covalence. Comparison be-
tween the physical properties of Rutile compounds and of TX2O4 is a subject of great
interest, but a magnetic investigation concerning TX2O4 has not been reported up to
now except for the results of neutron-scattering experiments at low temperatures [4, 5].
Thus we have performed a series of magnetic measurements on one member of the
TX2O4 family, MnSb2O4 (antiferromagnet: TN = 60 Æ 5 K and ordered magnetic mo-
2+
2+
ment at 4.5 K = 5.1 Æ 0.3mB [4, 5]), and studied the effects of Mn /V substitution on
its magnetic behavior.
Sample Preparation Specimens were prepared by solid-state reaction of the mono-oxi-
des of Mn, V and Sb2O3 following the formula
(1 –– x) MnO + x VO + Sb2O3 ! (Mn1 –– xVx)Sb2O4 (x = 0 to 0.6) .
1)
e-mail: ABE.hideki@nims.go.jp
Corresponding author; Tel.: +81-298-59-2732; Fax: +81-298-59-2701;
#
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430
H. Abe et al.: Magnetic Properties of (Mn1ꢁxVx)Sb2O4 with Magnetic Arrays
Fig. 1. Perspective view of the TX2O4 structure. TO6 units are
represented as shaded octahedra, and black spheres denote X
ions. The rectangle shows the unit cell
One of the starting compounds, MnO, was prepared by
hydrogen reduction of MnO2. Moss-green powder of
MnO was obtained by heating black MnO2 powder at
ꢀ
7
00 C for 12 h under flow of a H2/Ar gas mixture. An-
other starting compound, VO, was prepared by direct
reaction between the V metal and V2O3. Black V2O3
powder was pressed into tablets and melted together with a stoichiometric amount of
metal vanadium using an arc furnace under pure argon atmosphere. Obtained VO but-
tons with graphite-like color were ground with a mortar in a dry box to avoid humidity
and oxygen. Stoichiometric amounts of MnO, VO and Sb2O3 powder were mixed with
a mortar, and pressed into pellets. The pellets were wrapped with Pt foil and sealed in
ꢀ
evacuated Pyrex ampoules. After heating at 600 C for 10 min, the specimens were
taken out of the ampoules and ground again. Tablets of the powdered specimens were
ꢀ
sealed in ampoules in the same manner as stated above and heated at 685 C for
30 min. The color of the obtained specimens of (Mn1 –– xVx)Sb2O4 (x > 0) was dark
brown, whereas that of the end compound MnSb2O4 is light green.
Homogeneity of the specimens was checked by X-ray diffractometry (XRD). Except
for a small fraction of residual MnO, all of the peaks are assigned by the crystallo-
graphic parameters (tetragonal P42/mbc, a = 0.600 nm, and c = 0.871 nm). It turned out
that the lattice parameters of the solid solution do not vary apparently from those of
the final compound. No traces of the other Mn oxides with higher valences (Mn2O3,
Mn3O4, or MnO2) were recognized.
Magnetic measurements were performed using a SQUID magnetometer (Quantum
Design Ltd., MPMS) under fields up to 5 Tand at temperatures ranging from 5 to 300 K.
Results and Discussion It was observed that the magnetic susceptibility of the solid
solution (Mn1 –– xVx)Sb2O4 changes drastically with increasing concentration of V (Fig. 2).
In the case of x = 0.1, the zero-field cooling magnetic susceptibility (ZFC) increases
with raising temperature up to the critical temperature Tc = 57K, where it shows a
maximum. The ZFC curve decreases steeply with an increase in temperature above Tc,
and keeps on decreasing moderately with increasing temperature up to 300 K. The
field-cooling susceptibility (FC) coincides with ZFC in the temperature range from
300 K down to Tc. FC tends to saturate below Tc, and the amplitude of FC becomes
about 20 times larger than that of ZFC at 5 K. The qualitative features of the magnetic
susceptibility for the other solid solution specimens (x = 0.2 and 0.6) are similar to the
above-stated case of x = 0.1, where the peak of ZFC at Tc grows with the increase in x.
It is worth noticing here that Tc for the specimens do not vary with the increase in x
within experimental errors, and are very close to the reported Ne e´ l point TN of the
final compound.
Results of ac measurements of the frequency dependence of the magnetic susceptibil-
ity are represented in the inset of Fig. 2. All of the curves correspond to the real parts

phys. stat. sol. (a) 189, No. 2 (2002)
431
Fig. 2. Temperature dependence of the mag-
netic susceptibility of (Mn1 –– xVx)Sb2O4 (x = 0
to 0.6) at 0.1 T. Crosses, squares, triangles,
and circles correspond to x = 0, 0.1, 0.2, and
0
.6, respectively. The inset shows the fre-
quency dependence of the susceptibility of
Mn0.8V0.2)Sb2O4 at around Tc. Circles,
(
squares, crosses, and diamonds represent the
ac susceptibility at 0.8, 8, 80, and 800 Hz,
respectively
of the magnetic susceptibility. As is
seen in the inset, the frequency of the
applied magnetic field does not affect
the peak temperature Tc, instead the
peak height of the susceptibility at Tc is suppressed to some extent by the increase in
frequency.
Figure 3 shows magnetic isotherms of the (Mn1 –– xVx)Sb2O4 system at 5 K. In contrast
to the linear isotherm of the final compound, the other specimens include small
amounts of V and show ferromagnetic jumps at fields lower than 0.5 T. The magnetiza-
tion processes of the solid solution system form broad hysteresis loops, which give rise
to the large differences between FC and ZFC at low temperatures (see Fig. 2). The
amplitudes of the spontaneous magnetization increase with increasing x, whereas the
coercivity does not change apparently (Fig. 3). It is also noticeable that the magnetiza-
tion curves at high magnetic fields indicate no tendency to saturation.
Magnetic isotherms of (Mn0.8V0.2)Sb2O4 at various temperatures are summarized in
Fig. 4. The coercive forces decrease gradually to zero with increasing the temperature
from 5 to 52 K, whereas the spontaneous magnetization remains almost constant up to
52 K. Above 52 K, the ferromagnetic jump at zero field is suppressed steeply by the in-
crease in temperature. When the temperature exceeds Tc = 57K, no ferromagnetic behav-
ior is observed any longer. The magnetic iso-
therm at 70 K shows a paramagnetic increase
with a convex curvature as a function of field.
Recently a magnetic study has been re-
ported on a tri-Rutile compound, CoSb2O6
[6, 7]. The tri-Rutile CoSb2O6 has the same
Fig. 3. Magnetic isotherms of (Mn1 –– xVx)Sb2O4
x = 0 to 0.6) at 5 K. Diamonds, circles, triangles,
(
and crosses correspond to x = 0, 0.1, 0.4, and 0.6,
respectively

432
H. Abe et al.: Magnetic Properties of (Mn1ꢁxVx)Sb2O4 with Magnetic Arrays
Fig. 4. Magnetic isotherms of (Mn0.8V0.2)Sb2O4 at
various temperatures. Circles, crosses, triangles,
and diamonds denote the isotherms at 5, 52, 70,
and 100 K, respectively
configuration of the magnetic ions as the
2+
TX2O4 structure: one-dimensional {Co O2}1
arrays along the c-axis are connected with
each other via Sb5+ ions. Moreover, the
magnetic susceptibility of this system shows
characteristic features similar to our
(Mn1 –– xVx)Sb2O4 (x > 0.1) system (Fig. 2).
ZFC of CoSb2O6 increases from zero to a broad maximum at around 50 K with in-
creasing temperature, whereas FC stands constant below 50 K. This behavior was ex-
plained as a result of spin-glass formation of the magnetic moments on the Co2 ions
+
[
6]. For our case, however, such spin-glass formation seems not to be a good explana-
tion. The independence of Tc of (Mn1 –– xVx)Sb2O4 (x > 0) of the frequency of fields
see inset of Fig. 2) does not accord with the high sensitivity of a typical spin-glass
(
2+
5
system to the frequencies of applied fields. It is thought that the Mn (d ions) sub-
2
+
3
stitution for V (d ions) does not give rise to frustration in the exchange coupling
of the magnetic ions. In addition to that, the independence of Tc on x (see Fig. 2)
suggests that the substitution does not affect the amplitudes of the antiferromagnetic
interaction themselves. A possible candidate to understand the magnetic behavior of
(
Mn1 –– xVx)Sb2O4 is, therefore, some ferromagnetism arising from the antiferromagnetic
2
+
2+
configuration of Mn and V ions. The amplitude of the ordered magnetic moments
2
+
of Mn in the final compound is 5.1 Æ 0.3mB at 4.5 K [4, 5], which indicates that the
5
2+
d electrons of the Mn ions are in the high-spin state with total spin S = 5/2. On
3
2+
the other hand, the total spin of the d electrons of the V ions is S = 3/2, regard-
less of the crystal electric fields. Assuming that the coupling between the d and d
3
5
ions is antiferromagnetic, the difference in the amplitudes of the magnetic moments
could bring about finite spontaneous magnetization as seen in Figs. 3 and 4.
In conclusion, we have found characteristic ferromagnetic behavior in the solid solu-
tion (Mn1 –– xVx)Sb2O4 with tetragonal TX2O4 structure. Further studies using micro-
scopic measurement techniques are necessary to clarify the details, above all, neutron
diffractometry at low temperatures.
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