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Structures and Magnetism of the Rare-Earth Orthochromite Perovskite Solid Solution La<sub><i>x</i></sub>Sm<sub>1–<i>x</i></sub>CrO<sub>3</sub>
A new mixed rare-earth orthochromite
series, La<sub><i>x</i></sub>Sm<sub>1–<i>x</i></sub>CrO<sub>3</sub>, prepared through single-step hydrothermal
synthesis is reported. Solid solutions (<i>x</i> = 0, 0.25,
0.5, 0.625, 0.75, 0.875, and 1.0) were prepared by the hydrothermal
treatment of amorphous mixed-metal hydroxides at 370 °C for 48
h. Transmission electron microscopy (TEM) reveals the formation of
highly crystalline particles with dendritic-like morphologies. Rietveld
refinements against high-resolution powder X-ray diffraction (PXRD)
data show that the distorted perovskite structures are described by
the orthorhombic space group <i>Pnma</i> over the full composition
range. Unit cell volumes and Cr–O–Cr bond angles decrease
monotonically with increasing samarium content, consistent with the
presence of the smaller lanthanide in the structure. Raman spectroscopy
confirms the formation of solid solutions, the degree of their structural
distortion. With the aid of shell-model calculations the complex mixing
of Raman modes below 250 cm<sup>–1</sup> is clarified. Magnetometry
as a function of temperature reveals the onset of low-temperature
antiferromagnetic ordering of Cr<sup>3+</sup> spins with weak ferromagnetic
component at Néel temperatures (<i>T</i><sub>N</sub>) that scale linearly with unit cell volume and structural distortion.
Coupling effects between Cr<sup>3+</sup> and Sm<sup>3+</sup> ions
are examined with enhanced susceptibilities below <i>T</i><sub>N</sub> due to polarization of Sm<sup>3+</sup> moments. At low
temperatures the Cr<sup>3+</sup> sublattice is shown to undergo a
second-order spin reorientation observed as a rapid decrease of susceptibility