ROOM TEMPERATURE SYNTHESIS OF COLOSSAL MAGNETO-RESISTANCE OF LA2/3CA1/3MNO3: AG0.10 COMPOSITE
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ECS Journal of Solid State
Science and Technology
OPEN ACCESS
Room Temperature Synthesis of Colossal Magneto-Resistance of
La2/3Ca1/3MnO3: Ag0.10 Composite
To cite this article: Navjyoti Boora et al 2021 ECS J. Solid State Sci. Technol. 10 027006
View the article online for updates and enhancements.
This content was downloaded from IP address 46.4.80.155 on 15/09/2021 at 21:26
ECS Journal of Solid State Science and Technology, 2021 10 027006
Room Temperature Synthesis of Colossal Magneto-Resistance of
La2/3Ca1/3MnO3: Ag0.10 Composite
Navjyoti Boora,1 Rafiq Ahmad,1 Poonam Rani,1,2 Pankaj Kumar Maheshwari,2
Ajit Khosla,3 Sonia Bansal,4 V. P. S. Awana,2 and A.K. Hafiz1,z
1
Centre for Nanoscience and Nanotechnology, Jamia Millia Islamia, New Delhi 110025, India
2
CSIR-National Physical Laboratory, Dr. K.S. Krishnan Marg, New Delhi 110012, India
3
Department of Mechanical Systems Engineering, Faculty of Engineering, Yamagata University, Yonezawa, Yamagata 992-
8510, Japan
4
Department of Physics, J. C. Bose University of Science and Technology, Haryana-121006, India
Rare-earth manganite-based perovskite has great potential as a promising material for spintronics and ferroelectromagnets. Herein,
we have synthesized La2/3Ca1/3MnO3:Silverx (LCMO-Agx; where x = 0.00 and 0.10) composite using a standard solid-state
reaction route. Their structural and physical properties have been investigated. Pristine LCMO and LCMO-Ag composite are
crystallized in an orthorhombic structure, which is in a single-phase and has a space group of Pbnm. Pristine LCMO and LCMO-
Ag composite’s structural analysis showed better grain connectivity in ferromagnetic domains of LCMO-Ag composite compared
to pristine LCMO. Ag doping enhances the paramagnetic-ferromagnetic transition Tc (Curie temperature) to 277 K, which is 8 K
higher than that of pristine LCMO (Tc = 269 K). Additionally, the magneto-resistance (MR) of LCMO-Ag composite was
improved by ∼10% with Ag doping even at room temperature (RT), which is due to improved connectivity and grain size with Ag
doping. Thus, the enhanced value of MR at RT may efficiently open up the possible use of LCMO-Ag composite as
ferroelectromagnets and spintronics applications. Additionally, LCMO thin films can be useful in artificial planar junctions, vertical
tunnel junctions, and sensing applications.
© 2021 The Author(s). Published on behalf of The Electrochemical Society by IOP Publishing Limited. This is an open access
article distributed under the terms of the Creative Commons Attribution Non-Commercial No Derivatives 4.0 License (CC BY-
NC-ND, http://creativecommons.org/licenses/by-nc-nd/4.0/), which permits non-commercial reuse, distribution, and reproduction
in any medium, provided the original work is not changed in any way and is properly cited. For permission for commercial reuse,
please email: permissions@ioppublishing.org. [DOI: 10.1149/2162-8777/abe58d]
Manuscript received January 8, 2021. Published February 22, 2021.
Rare earth-based manganese oxides have been a good candidate remains in grain boundaries (GB). After Ag addition, a significant
for scientific research now-a-days due to their extraordinary property improvement is observed in structural and magnetic properties of the
like colossal magneto-resistance (CMR).1–3 Application of magnetic sample with a pronounced increase in the Tc with reduced resistivity.
field changes the resistance of MR materials, dramatically. High MR Hence it is possible that Ag enters into the perovskite structure and varies
at room temperature is needed for practical applications, such as the Mn4+ content. Ag addition in pure LCMO causes a catalytic effect
bolometers and infrared sensors.4,5 Also, low resistivity is crucial for by promoting grain growth and improve grain boundary conductivity.
circuit-matching conditions. Colossal magneto-resistive mixed-va- The oxygenation effect due to Ag addition is the key factor of
lence manganite shows first-order phase transition from paramag- tremendous improvement in CMR properties. LCMO-Ag composite
netic to ferromagnetic and insulator to the metallic state upon materials can also be used as a magnetic sensor, position sensor,
cooling with a sheer drop in resistivity.6–9 CMR effect crucially information recording devices, high-density memory cells, and magnetic
depends on manganese (Mn3+ /Mn4+) ions ratio, which is controlled refrigeration due to their magneto-caloric properties.8,28–31
by Ca2+ and oxygen content in LCMO. Among materials that show In this report, we demonstrate the enhancement in magneto-
MR effect, La2/3Ca1/3MnO3 (LCMO) composite is most popular. transport properties of LCMO with the addition of Ag using a
LCMO shows more metal-insulator (MI) transition temperatures and standard solid-state reaction route. LCMO-Ag composite showed
curie points.10–17 LCMO has a perovskite-type structure that shows enhanced electrical and magnetic homogeneity. We studied en-
ferromagnetic ordering in magnetic Mn-O layers, which is parted by hancement in MR after the addition of Ag in perovskite manganite
La (Ca)-O layers that are non-magnetic.18 and obtained MR of ∼50% with 10 Tesla applied field and Tc
In LCMO, charge-ordered (CO) state happens due to the orderly (∼277 K) for LCMO-Ag composite.
alignment of Mn3+ /Mn4+ ions that hinders conduction electrons
movement. The ferromagnetic-metallic state (FMM) and antiferro-
magnetic insulating state occur in LCMO, which makes glass-like Experimental
system arrest. LCMO is oxygen stoichiometric. And on applying the Pristine LCMO and LCMO-Ag composite synthesis.—A con-
magnetic field, the CO state goes away and gives huge negative ventional solid-state reaction route has been employed to synthesize
magneto-resistance. A sequence of CMR manganites both in ceramics pristine LCMO and LCMO-Ag composite. Stoichiometric amounts
and thin film form have been reported earlier by researchers to explore of La2O3, CaCO3, and MnO2 are mixed and ground thoroughly.
the probability of their usage in bolometry.19 The Tc (Curie tempera- The mixture has been calcined at 1000 °C for 24 h with the heating
ture) and TMI (metal-insulator transition temperature) of LCMO are rate of 2 °C min−1 through pre-sintering at 1050 °C, 1100 °C, and
below room temperature (RT), which inhibits its successful application 1150 °C for 24 h. At each above temperature, the intermediate
in photo-electronic/magneto-electric devices. grindings are done until the phase purity is not achieved. Finally,
Various attempts are made to increase MR in LCMO composites.20,21 the powders are pelletized and sintered at 1180 °C for 48 h after the
An optimized reasonable MR is observed in LCMO at low magnetic addition of Ag and naturally cooled to RT. A schematic along with
fields but below RT (
ECS Journal of Solid State Science and Technology, 2021 10 027006
Figure 1. Schematic (along with optical images) diagram of LCMO and LCMO-Ag composite synthesis process.
scanning-electron-microscopy; Zeiss, Sigma). Magneto-transport prop-
erties were measured using commercial apparatus physical property
measurement system (Cryogenics Limited, USA) via applying a
magnetic field. Magnetization is measured as a function of temperature
(M-T) on a vibrating sample magnetometer (Lakeshore; VSM 7410 s)
at 10 kOe.7
Results and Discussion
Pristine LCMO and LCMO-Ag composite’s structural charac-
terizations.—Figure 2 depicts the Rietveld fitted RT X-ray diffrac-
tion patterns of LCMO and LCMO-Ag composite. As-synthesized
LCMO and LCMO-Ag composite are crystallized. The LCMO is
orthorhombic and has Pbnm space group without any detectable
impurities, where, a, b, and c are ∼5.45 Å, ∼7.71 Å, and ∼5.47 Å,
respectively, are refined lattice parameters.1,3 However, after Ag
addition there is a slight change in the lattice parameters in LCMO
(Table I). The goodness of fitting, χ2 showed smaller values and
depicted that the calculated values are well consistent with the
observed ones. The lattice parameters and structure of pristine
LCMO remain unchanged with the addition of Ag into the LCMO
matrix, which shows that Ag remains as an additive in the system
and segregated on the surfaces but not substituted in the main
LCMO lattice. The absence of Ag peak in the XRD pattern of
LCMO-Ag shows that most of the Ag are at GB and Ag+ does not Figure 2. Rietveld fitted X-ray diffraction patterns of LCMO and LCMO-
substitute at La3+ and Ca2+ sites. Ag composite.
Figures 3a–3d depict LCMO and LCMO-Ag composite FESEM
images, respectively at low and high resolutions. From FESEM
images, pristine LCMO surfaces are slightly blurry (a)–(b), however,
there is an improvement in image clarity of LCMO-Ag composite size is a crucial parameter, which increases the electrical and
(c)–(d) due to the addition of Ag in the LCMO matrix. In LCMO-Ag magneto-transport properties.6 Better FM coupling in domains and
composite, the grain size is increased that provides better grains conducting GB gives a positive change in the physical properties of
connectivity, which further enhances crystallization. Fine distribu- manganite.
tion of Ag in LCMO-Ag composite at the grain boundaries but a
slightly bigger grain size is observed in LCMO-Ag composite. Ag Magneto-transport properties measurements.—Resistance vs
acts as a catalyst and improves the homogeneity, grain growth, and Temperature (R-T) plots for LCMO and LCMO-Ag composite at
crystal structure of LCMO composites. Also, Ag is volatile above an applied magnetic field of zero and 5 Tesla in 50–300 K
1000 °C so it is added at the final sintering to get the desired temperature range, see Figs. 4a and 4b, respectively. R-T measure-
stoichiometry. Shreekala et al. reported that improvement in grain ments have been performed using the standard four-probe technique.
Table I. Table shows the calculated lattice parameters, TIM, TC, and MR for LCMO and LCMO-Ag composite.
Sample a(Å) b(Å) c(Å) V(Å3) χ2 TIM (K) Tc (K) MR (300 K–10 Tesla)
LCMO 5.459 7.712 5.477 230.641 5.23 278.2 269.3 40.29
LCMO-Ag composite 5.463 7.715 5.472 230.666 5.26 277.7 276.7 49.82
ECS Journal of Solid State Science and Technology, 2021 10 027006 Figure 3. (a)–(b) FESEM images of pristine LCMO and (c)–(d) LCMO-Ag composite at low and high resolutions. Both, LCMO and LCMO-Ag composite are sensitive to the gets sharper. Better results can be obtained by further optimizing and temperature and clearly show paramagnetic insulator to ferromag- making a thin film, which can also be used for magnetic sensing, netic metal behavior at a characteristic TMI ( TMI (
ECS Journal of Solid State Science and Technology, 2021 10 027006
Figure 4. R-T plot of pristine LCMO (a) and LCMO-Ag composite (b) measured in the applied magnetic fields of 0 and 5 Tesla, respectively.
composite, however, it is surprising that the non-magnetic Ag
increases the saturation magnetization and it suggests better coupling
of ferromagnetic domains. After Ag addition, the homogeneity of
LCMO is improved, which in turn suppresses the magnetic
scattering at grain boundaries. The PM-FM transition becomes
sharper with an increase in Ag content. The Tc is obtained from 1/
M vs T (shown in Fig. 6b) and the inflection point of dM/dT vs T
(shown in Fig. 6c) plots. The derivative shows a minima at 269 K for
LCMO and 277 K for LCMO-Ag composite. Tc is seen to go up with
Ag addition. There is 8 K change in Tc after the addition of Ag.
Table I shows the comparative variation in lattice parameters, TMI,
Tc, and MR for LCMO and LCMO-Ag composite. The addition of
Ag doesn’t affect the lattice parameters but greatly enhanced the
electrical and magnetic properties of pristine LCMO, which is
verified by a pronounced change in Tc and magnetoresistance.
Conclusions
In conclusion, we have successfully synthesized bulk
La2/3Ca1/3MnO3:Agx, where x = 0.0 and 0.10 composite of Ag
via conventional solid-state reaction route. Rietveld refinement of
XRD confirmed the single crystalline phase of orthorhombic
Figure 5. MR measurement as a function of perpendicular magnetic field structure with Pbnm space group. An expanded crystal volume is
up-to 10 Tesla at RT for LCMO and LCMO-Ag composite. observed after Ag addition. Tc is improved to be 277 K for x = 0.10
ECS Journal of Solid State Science and Technology, 2021 10 027006
Figure 6. (a)–(b) Magnetization [(M vs T) and (1/M vs T)] and (c) derivative (dM/dT vs T) in an applied magnetic field of 10 kOe for LCMO and LCMO-Ag
composite.
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