Tuning the magnetic anisotropy via Mn substitution in single crystal CO4Nb2O9

By using the optical floating-zone technique to grow a series of high-quality Co4-xMnxNb2O9 single crystals, the effect of Mn doping on the magnetic anisotropy and spin-flop is investigated. The antiferromagnetic phase transition and spin-flop transition for these samples (x <= 3.9) are similar to those in the parent phase of Co4Nb2O9, revealing that Co2+ ions in Co4-xMnxNb2O9 possess a strong single-ion anisotropy. The critical doping content, above which the magnetic anisotropy changes from easy-plane to easy-axis, has been identified as x = 3.95 with an additional kink observed in the magnetization curve below the N eel temperature. A spin-flop transition is reported for the first time in Mn4Nb2O9 at a field of 10.9 T at 2K.