Hydrothermal synthesis and magnetic studies of transition metal nocerites M-3(BO3)F-3 (M = Fe, Co, Ni)

Polycrystalline samples of M-3(BO3)F-3 (M=Fe, Co, Ni), isostructural with n ocerite Mg-3(BO3)(OH,F)(3), have been prepared in supercritical hydrotherma l conditions. These compounds represent with boracites, M3B7O13F (M= Mg, Cr , Mn, Fe, Co, Zn), the only transition metal fluoride borates known to date . Co-3(BO3)F-3 and Ni-3(BO3)F-3 are antiferromagnetic with T-N = 17(2) and 40(2) K, respectively. Spin-flop transitions at B-C1 = 4.0 T and B-C2 = 7.5 T occur at 1.6 K in Co-3(BO3)F-3, while a parasitic ferromagnetism (0.02 m u (B)/Ni2+ at 1.6 K) appears below T-N in Ni-3(BO3)F-3. The magnetic struct ures consist of three spin sub-lattices of double rutile-type ferromagnetic chains. (C) 2001 Elsevier Science B.V. All rights reserved.