Field-induced spin-flop-like metamagnetism in α-CoB4O7

We successfully obtained pure α-CoB4O7 powder sample by a two-step synthesis method. First, a new cobalt polyborate with unknown crystal structure was synthesized by boric acid flux method in a sealed system. Subsequently, α-CoB4O7 powder was obtained by the thermal decomposition of this new phase at 800 °C. The purity was carefully checked by Le Bail fitting of its powder XRD with good convergence. The magnetic susceptibilities in paramagnetic region agree well with Curie–Weiss law with θ = −17.7 K, C = 3.13 cm3 K mol−1. Ac magnetic measurements confirm its long-range AFM ordering at ∼5 K. The field-dependent magnetization curve at 1.85 K indicates a spin-flop-like phase transition, with Hc = 35 kOe. Considering the relatively weak magnetic super-exchange, we believe this transition is due to the large magnetic anisotropy of Co2+.

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► Pure polycrystalline α-CoB4O7 is prepared by two-step synthesis method.
► Dc and ac magnetic susceptibilities show an AFM ordering at ∼5 K.
►  Isothermal magnetization curve at 1.85 K shows a spin-flop-like transition.
► High critical field (35 kOe) may relate to the large magnetic anisotropy of Co2+.