• The synthesis of homogeneous phase pure RCrO 4 and RCrO 3 nanoparticles, • The stabilization of metastable Cr5+ (4s03d1) state in RCrO 4 compounds, by employing high pressure during the synthesis, which is otherwise very difficult to stabilize by other synthetic routes, • The dependence of formation of the crystal structure on the particle size, assisted by the temperature. • The determination of closely spaced T C and T N due to FM and AFM interactions in RCrO 4 that gives rise to metamagnetism, • The alignment of magnetic sublattices (and/or ions) of R and Cr in the light of negative magnetization and spin-reorientation of RCrO 3 , and. • The analysis of χ - χ 0 - 1 vs. T plots for of χ 0 = 0 and χ 0 ≠ 0 in the high-T region to understand the contribution of magnetic moment of different ions in the PM regime of RCrO 4 and RCrO 3. • Towards these objectives, we report the synthesis of homogeneous single phase RCrO 4 and RCrO 3 (R = Sm, Gd, Dy and Er) nanoparticles through a modified sol–gel route followed by hydrothermal method followed by annealing and confirmation of the formation of respective zircon-type tetragonal RCrO 4 (S.G. I41/amd, D 4 h 19 symmetry) and orthorhombic RCrO 3 (S.G. Pbnm, D 4 h 19 symmetry) through the analysis of powder X-ray diffraction. The temperature-dependent DC magnetization data reveals the (obvious) different magnetic transition temperatures, T C and T N , and spin-reorientation temperature, T SR. The analysis of χ - χ 0 - 1 vs. T plots in the high temperature region (far from magnetic transition) highlight RCrO 4 nanoparticles exhibit modified Curie-Weiss behavior. On the other hand, the analysis of χ - χ 0 - 1 vs. T plots for χ 0 = 0 shows RCrO 3 nanoparticles obey Curie-Weiss behavior (discussed in the later part). The M−H isotherms on the RCrO 4 nanoparticles demonstrate the presence of competing ferromagnetic and antiferromagnetic exchange interactions that leads to metamagnetism. The M−H plots on RCrO 3 nanoparticles display the existence of canted antiferromagnetic interactions. We report the synthesis of homogeneous single-phase nanoparticles of RCrO 4 and RCrO 3 (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+ (4 s 03 d 1) state by crystallizing into a zircon-type tetragonal RCrO 4 (S.G. I41/amd, D 4 h 19 symmetry) structure at 773 K, while it chooses to form orthorhombic RCrO 3 (S.G. Pbnm, D 4 h 19 symmetry) structure with a stable Cr3+ (4 s 03 d 3) state at 973 K. The analysis of DC magnetization (M) versus temperature (T) in an external magnetic field, H = 100 Oe for polycrystalline RCrO 4 indicates the magnetic transition temperatures, T C ∼ 20 K. The derivative of zero-field cooled magnetic susceptibility with respect to T, d χ Z F C d T , versus T, indicates the presence of competing magnetic interactions due to the ferromagnetic (FM) and antiferromagnetic (AFM) ordering of Cr5+ and R3+ in RCrO 4 respectively near magnetic transition. This feature specifies magnetic frustration that leads to metamagnetism in RCrO 4. The fit of non-linear magnetic susceptibility, χ = M H , to χ = χ 0 + C T - θ , with a non-zero χ 0 determined from high-T data gives effective magnetic moment, μ e f f , which is in accordance with the theoretical value. The analysis of M vs. T indicates that RCrO 3 undergoes a paramagnetic (PM) to canted-antiferromagnetic (CAFM) transition of Cr sublattices at Néel 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 χ - 1 vs. T with a zero χ 0 shows Curie-Weiss law is more appropriate at T > T C resulting expected μ eff values for RCrO 3. [ABSTRACT FROM AUTHOR]