We studied the effect of Dy3+ content on the magnetic properties of cobalt ferrite single crystal. The single crystals of CoFe1.9Dy0.1O4 were grown by the flux method using Na2B4O7 center dot 10 H2O (Borax) as a solvent (flux). The black and shiny single crystals were obtained as a product. The X-ray diffraction analysis at room temperature confirmed the spinel cubic structure with lattice constant a = 8.42 angstrom of the single crystals. The compositional analysis endorses the presence of constituents Co, Fe and Dy elements after sintering at 1300 degrees C within the final structure. The magnetic hysteresis measurements at various temperatures viz. 10 K, 100 K, 200 K and 300 K reveal the soft ferrimagnetic nature of the single crystal than that of for pure CoFe2O4. The observed saturation magnetization (M-s) and coercivity (H-c) are found to be lower than that of pure CoFe2O4 single crystal. The magnetostriction (lambda) measurement was carried out along the [001] direction. The magnetic measurements lead to conclude that the present single crystals can be used for magneto-optic recording media. (C) 2011 Elsevier B.V. All rights reserved.