A II-VI diluted magnetic semiconductor of (Cd1-x-yMnxHgy)(Te1-zSez) crystal with 0.1 < x < 0.3, 0.1 < y < 0.3, 0 < z 0.02 has a high Hg vapor pressure at a temperature of crystal growth from a melt and has also temperature-composition phase diagrams with a wide solid solution. The composition dependence of a figure of merit F (rotation/absorption) greater than or equal to 250 degrees /dB at 0.38 T at 0.98 mum was improved by adding selenium. A quenched-annealed ingot with compositional uniformity in both the axial and radial directions was scaled up for large size (20 mm diam by 15 mm length) by the hot isostatic pressure method in which a seated quartz ampul was subjected to a high external pressure of argon gas. Using this quenched-annealed polycrystal ingot, a crystal with compositional homogeneity in the axial direction has been grown by a zone-melt method for the first time.