Effect of low Fe doping in La0.8Sr0.2MnO3
Antony Ajan, N. Venkataramani, Shiva Prasad, S. N. Shringi, A. K. Nigam et al.
Citation: J. Appl. Phys. 83, 7169 (1998); doi: 10.1063/1.367629
View online: http://dx.doi.org/10.1063/1.367629
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Published by the American Institute of Physics.
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JOURNAL OF APPLIED PHYSICS
VOLUME 83, NUMBER 11
1 JUNE 1998
Effect of low Fe doping in La0.8Sr0.2MnO3
Antony Ajana)
Department of Physics, Indian Institute of Technology, Powai, Bombay 400 076, India
N. Venkataramani
ACRE (Advanced Center for Research in Electronics), Indian Institute of Technology, Powai,
Bombay 400 076, India
Shiva Prasad and S. N. Shringi
Department of Physics, Indian Institute of Technology, Powai, Bombay 400 076, India
A. K. Nigam and R. Pinto
Tata Institute of Fundamental Research, Homi Bhabha Road, Bombay 400 005, India
The effect of low Fe substitution in Mn sites of La0.8Sr0.2MnO3 is presented. We report the electrical
and magnetic properties of these materials in the Fe concentration range x50 to x50.1. The
metal-insulator transition temperature is found to vary significantly with very small Fe doping. The
metal to insulator transition temperature increases slightly when a very small amount of Fe is doped
(,1%) and then it decreases significantly with further doping of Fe. The magnetic moment of
La0.8Sr0.2MnO3 decreases almost linearly with Fe doping at room temperature. © 1998 American
Institute of Physics. @S0021-8979~98!26811-3#
I. INTRODUCTION
The calcined powder was remilled and the compacts were
sintered at 1300 °C in air for 6 h. The fired samples were
characterized by x-ray diffraction, with a -Al2O3 used as the
internal standard. Resistivity studies were carried out on 2mm-thick rectangular samples. Resistivity measurements
were carried out for all the samples in the temperature range
from 15 to 473 K by conventional four-probes method. In the
range 15–300 K a closed cycle refrigerator was employed to
cool the sample and for high temperature studies ~room temperature to 473 K! a variable temperature oil bath was used.
Room temperature magnetization studies were carried out by
using a vibrating sample magnetometer ~VSM! setup with a
maximum field of 0.4 T.
Giant magnetoresistance ~GMR! effect shown on the
perovskite oxide materials has attracted alot of research interest. The metal-insulating transition temperature (T tr) is
known to be dependent on the Mn–O–Mn bond angle and
bond length. Double exchange1–3 has been used to explain
qualitatively the transport phenomena as well the magnetic
ordering observed in these perovskite oxides. The insulating
material LaMnO3 when doped with divalent ions such as Ca,
Sr, Ba, Pb, etc. causes a conversion of proportional number
of Mn31 to Mn41. The electron hopping between the mixed
Mn valence states then causes ferromagnetic ordering and
metallic conduction in these systems.2
Up to date, much exploration of the GMR perovskite
materials has been done through doping of La sites with rare
earths ~Y, Nd, Pr, etc.! of different sizes, which brings strong
lattice effects thus influencing the double exchange.4,5 However, very few studies have been carried6–8 out to observe
the effects of transition metal ion doping on Mn sites, which
will bring out the changes in electronic structure thus influencing double exchange. Effect of large doping of Fe
~.10%! on La0.8Ax MnO3 ~where A5Sr, Ca, Ba, Pb! systems and its magnetic ordering has been reported earlier by
Banks et al.9 However, the effect of lower Fe doping
~,10%! has not been reported on a systematic study. In this
article we report the effect of low Fe(,10%) doping on Mn
sites of La0.8Sr0.2MnO3 system.
III. RESULTS AND DISCUSSION
The x-ray diffraction ~XRD! spectra of samples with extreme concentration of Fe ~x50, 0.1! are shown in Fig. 1. It
is clearly seen from the figure that both the samples shows
similar XRD pattern. XRD spectra for all the other samples
between these concentrations are also found to be similar.
The XRD spectra were indexed by assuming a pseudocubic
structure. The lattice constants were found to be 3.8790 and
3.8811 Å for x50 and x50.1, respectively. The studies of
Fe doping on Ca containing LaMnO3 systems (.10%) 7 also
does not show any changes in the lattice parameter. Studies
by Jian et al.8 also showed that the lattice parameter of
La0.67Ca0.33Mn12x Fex O3 remains nearly identical, i.e.,
3.8571 Å for x50.0 and 3.8561 Å for x50.1. This indicates
that the doping of Fe has hardly any influence on lattice
parameter. This could be because of the identical ionic
sizes10 of Fe31 and Mn31.
In Fig. 2 the variation of normalized resistance with temperature is shown. All the samples show a metal-insulator
transition temperature. At low temperature, for all the
samples, the resistance curve tends to flatten out. Transition
II. EXPERIMENTAL DETAILS
The samples were prepared by the conventional solid
state technique by taking Fe2O3, MnC2O4, SrCO3 , and
La2O3 in appropriate stoichiometric proportion as the starting
material. These powders were milled and calcined at 900 °C.
a!
Electronic mail: [email protected]
0021-8979/98/83(11)/7169/2/$15.00
7169
© 1998 American Institute of Physics
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7170
Ajan et al.
J. Appl. Phys., Vol. 83, No. 11, 1 June 1998
FIG. 1. XRD spectra for the samples La0.8Sr0.2Mn12x Fex O3 with x50 and
0.1.
temperature is found to be strongly dependent of the Fe doping even at low concentrations.
For the parent sample, i.e., La0.8Sr0.2MnO3 the transition
temperature is found to be 350 K which is agreeing with the
reported values for the Sr composition 0.2.11 Transition temperature T tr increases when doped with small amount of Fe
('0.005) and then it decreases systematically with the addition of Fe content and for x50.1, transition temperature
was found to be '260 K. Recently Ahn et al.7 showed that
in the Ca containing LaMnO3 system both in the ferromagnetic as well as the antiferromagnetic region the transition
temperature is varying with respect to the Fe doping
(.10%). In the ferromagnetic region transition temperature
decreases with increase in Fe concentration. The decrease in
the transition temperature with Fe doping could be due to the
FIG. 3. Variation of magnetic moment with different concentration of Fe in
La0.8Sr0.2Mn12x Fex O3, 0,x,0.1.
replacement of Fe31 on Mn31 thus reducing the double exchange interaction.
Magnetization studies on these systems indicates the ferromagnetic nature of the samples. The variation of magnetic
moment of the sample with Fe concentration at room temperature is shown in Fig. 3. With the Fe doping the magnetic
moment of the sample decreases. The magnetic moment decreases almost linearly with the Fe doping. Magnetic moment decreased from 2.52 to 0.2 m B for x50 and x50.1,
respectively. In the case of Ca containing systems7 the decrease of magnetic moment is found to be from 3.2 to 2 m B
for x50 to x50.1 at 5 K.
IV. CONCLUSION
The lattice parameter of La0.8Sr0.2MnO3 does not change
with Fe concentration. Metal-insulator transition temperature
was found to increase at a very low concentration of Fe
~,1%! and decreases with further addition of Fe. Magnetic
moment of the samples decreases sharply even at very low
concentration of Fe.
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1
2
FIG. 2. Temperature dependence of normalized resistance for Fe doped
samples La0.8Sr0.2Mn12x Fex O3, 0,x,0.1.
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