Temperature assisted size dependent synthesis and magnetic properties of rare-earth chromium oxide nanoparticles

We report the synthesis of homogeneous single-phase nanoparticles of RCrO4 and RCrO3 (R = Sm, Gd, Dy, and Er) compounds using a modified sol-gel hydrothermal method followed by heat treatment. Annealing of the asprepared powder sample at ambient pressure enables chromium to remain in the metastable Cr5+ (4s(0)3d(1)) state by crystallizing into a zircon-type tetragonal RCrO 4 (S.G. I41/amd, D-4h(19) symmetry) structure at 773 K, while it chooses to form orthorhombic RCrO3 (S.G. Pbnm, D-4h(19) symmetry) structure with a stable Cr3+ (4s(0) 3d(3)) state at 973 K. The analysis of DC magnetization (M) versus temperature (T) in an external magnetic field, H = 100 Oe for polycrystalline RCrO4 indicates the magnetic transition temperatures, T-C similar to 20 K. The derivative of zero-field cooled magnetic susceptibility with respect to T, d(chi ZFC)/dT, versus T, indicates the presence of competing magnetic interactions due to the ferromagnetic (FM) and antiferromagnetic (AFM) ordering of Cr5+ and R3+ in RCrO4 respectively near magnetic transition. This feature specifies magnetic frustration that leads to metamagnetism in RCrO4. The fit of non-linear magnetic susceptibility, chi = M/H, to chi = chi(0) + C/T-theta, with a non-zero chi(0) determined from high-T data gives effective magnetic moment, mu(eff), which is in accordance with the theoretical value. The analysis of M vs. T indicates that RCrO3 undergoes a paramagnetic (PM) to canted-antiferromagnetic (CAFM) transition of Cr sublattices at Neel temperature (T-N(Cr)) because of antisymmetric Dzyaloshinskii-Moriya (DM) interaction due to Cr-O-Cr superexchange with a possible antiferromagnetic (AFM) ordering of the rare-earth at low temperature (T-N(R) < 20 K). The linear fit of chi(-1) vs. T with a zero chi(0) shows Curie-Weiss law is more appropriate at T > T-C resulting expected mu(eff) values for RCrO3.

Automated summary

This study reports the synthesis of homogeneous single-phase nanoparticles of RCrO4 and RCrO3 compounds using a modified sol-gel hydrothermal method. The different crystal structures and magnetic properties of RCrO4 and RCrO3 were determined through annealing and magnetization analysis.