Tuning the Structure and Magnetic Phases of Rareearth Chromium Oxides at Nanoscale
Y. Sundarayya, 1, 2 Rajesh Sondge, 1 K. Ashwini Kumar, 1 S. Srinath 1,* and S.N. Kaul1
1 School of Physics, University of Hyderabad, Hyderabad – 500046, India.
2 Department of Physics, School of Sciences, Nagaland University, Lumami, Nagaland – 798627, India.
*
Corresponding author’s e-mail:srinaths10@gmail.com, Tel.: +91-9440491259; Fax: +91-413-2655734
Abstract
Monodisperse single phase DyCrO4 and DyCrO3
nanoparticles are synthesized by a modified-hydrothermal
method, followed by tuning the annealing temperatures. X-ray
diffraction reveals that DyCrO4 crystallizes in to tetragonal
structure with space group I41/amd, while the DyCrO3
crystallizes in to orthorhombic structure with space group
Pnma. DC magnetic measurements show that the magnetic
behavior of DyCrO4 is solely dependent on the Dy3+ with a
Néel temperature (TN) 21K, while the combined magnetic
behavior of Dy3+ and Cr3+ results in a canted
antiferromagnetic structure below TN (~143K) for DyCrO3.
formula are 20 (1) nm and 40 (1) nm respectively.
Morphological studies by means of field-emission
scanning electron microscopy show that the particles
have uniform size distribution.
Keywords: Antiferromagnetism, Sol-gel, Nanocrystalline
materials, Perovskite
Introduction
The combination of chromium with rare-earth
(R) forms variety of oxides such as RCrO 4 and RCrO3,
depending on the synthesis conditions. The formation of
RCrO4 requires a controlled oxygen atmosphere
whereas RCrO3 can be synthesized in ambient oxygen
environment [1 -3]. While Chromium is stabilized in an
unusual oxidation state of +5 in RCrO4 so that it does
not contribute to the magnetic property, RCrO3 has a
canted antiferromagnetic structure below T N due to the
antisymmetric Dzyaloshinsky-Moriya (DM) exchange
interaction between neighboring Cr3+ spins [4].
Experimental details
Monodisperse amorphous powder has been
synthesized using a modified sol-gel followed by
hydrothermal method using nitrates of Dysprosium and
Chromium [5].This was followed by tuning the
annealing temperatures at 773 K and 1073 K in air for
12 h to obtain single phase DrCrO4 and DyCrO3
nanoparticles respectively.
Results and Discussion
The Rietveld profile matching of the XRD patterns of
the samples annealed at 773 K and 1073 K reveal the
samples crystallizes into tetragonal and orthorhombic
structures with space group I41/amd, and Pnma
respectively, thus confirms the presence of DyCrO4 and
DyCrO3 phases. The obtained lattice parameters of
DyCrO4 and DyCrO3 are a = b = 6.9630 Å, c = 6.1161
Å and a = 5.2766 Å, b = 5.5443 Å, c = 7.5793 Å
respectively. The average crystallite sizes of DyCrO4
and DyCrO3 nanoparticles estimated from the Scherer’s
Fig. 1: ZFC and FC magnetization of (a) DyCrO4 and
(b) DyCrO3 nanoparticles.
The ‘zero-field-cooled’ (ZFC) and ‘field-cooled’ (FC)
DC magnetizations in the temperature range 2 K ≤ T ≤
50 K on DyCrO4 and DyCrO3 nanoparticles in the
presence of external magnetic field H = 100 Oe are
shown in Figures 1(a) and 1(b). The observed TN for
DyCrO4 and DyCrO3 are respectively 21 and 143 K.
Further analysis show the presence of antiferromagnetic
spin correlations in DyCrO4 and the magnetic moment
on Dy3+ completely accounts for the observed moment.
Conclusions
Monodisperse single phase DyCrO4 and DyCrO3
nanoparticles have been synthesized using the same
amorphous powder by annealing at different
temperatures. The structure, microstructure and
magnetic properties are investigated.
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