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

Abstract

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 as-prepared powder sample at ambient pressure enables chromium to remain in the metastable Cr5+ (4s03d1) state by crystallizing into a zircon-type tetragonal RCrO4 (S.G. I41/amd, D4h19 symmetry) structure at 773 K, while it chooses to form orthorhombic RCrO3 (S.G. Pbnm, D4h19 symmetry) structure with a stable Cr3+ (4s03d3) 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, TC ∼ 20 K. The derivative of zero-field cooled magnetic susceptibility with respect to T, dχZFCdT, 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, χ=MH, to χ=χ0+CT-θ, with a non-zero χ0 determined from high-T data gives effective magnetic moment, μeff, 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 Néel temperature (TNCr) 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 (TNR < 20 K). The linear fit of χ-1 vs. T with a zero χ0 shows Curie-Weiss law is more appropriate at T>TC resulting expected μeff values for RCrO3.