Structures and Magnetism of the Rare-Earth Orthochromite Perovskite Solid Solution LaxSm1−xCrO3

A new mixed rare-earth orthochromite series, LaxSm1−xCrO3,
prepared through single-step hydrothermal synthesis is reported. Solid solutions
(x = 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
Pnma 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−1 is clarified. Magnetometry as a function of
temperature reveals the onset of low-temperature antiferromagnetic ordering of Cr3+ spins with weak ferromagnetic component
at Néel temperatures (TN) that scale linearly with unit cell volume and structural distortion. Coupling effects between Cr3+ and
Sm3+ ions are examined with enhanced susceptibilities below TN due to polarization of Sm3+ moments. At low temperatures the
Cr3+ sublattice is shown to undergo a second-order spin reorientation observed as a rapid decrease of susceptibility.