Effects of Cr doping and size reduction on the structural and magnetic properties of α–CoV₂O₆

We report the effect of Cr-doping on the structural and magnetic properties of powder α–CoV₂O₆ samples. Samples were synthesized using a wet chemical synthesis method and calcined at temperatures between 350 ℃ and 500 ℃ to promote phase formation. For α–CoV₂O₆ and Cr-doped α–CoV₂O₆ samples, a single phase only occurs when the samples are calcined at 450 ℃ and 500 ℃, respectively, as confirmed using powder x-ray diffraction (XRD). Cr-doping results in a compression distortion of the lattice along the c-axis. Transmission electron microscopy (TEM) measurements indicate that Cr-doping causes a reduction in particle size and particle agglomeration. Metamagnetism was observed in field dependence of magnetization, M(μ₀H) for α–Co(V_1−xCr_x)₂O₆ samples with 0 ≤ x ≤ 0.05. The hysteresis in M(μ₀H) curves for μ₀H < 5 T at 2 K indicate that the magnetization is metastable and suggests magnetic irreversibility. Zero-field-cooled (ZFC) and field-cooled (FC) temperature dependence of magnetization, M(T), show antiferromagnetic (AFM) ordering of the α–Co(V_1−xCr_x)₂O₆ samples at fields, μ₀H ≤ 1 T. Increasing field strength to 2.5 T causes a transition from the AFM state to a ferrimagnetic (FI) state, and an introduction of spin-glass (SG)-like behavior. At 5 T, a transition from the FI state to a ferromagnetic (FM) state and a suppression of SG-like behavior is observed.