High-Field Magnetization of the Distorted Spin Frustration System Ni-5(TeO3)(4)Br-2

We performed high-field magnetization measurements, M(H), on the Ni-5(TeO3)(4)Br-2 by using a pulse magnet. The Ni2+ ions (S = 1) of this compound form a two dimensional distorted spin frustrated system (distorted kagome lattice), and undergo a Neel transition at T (N) similar to 29 K, due to the anisotropy. Below T (N) , a complex spin arrangement which contains ten spin sub-lattices was suggested by neutron scattering and electron spin resonance studies. We observed a step-like transition at H (c) similar to 11 T when T < T (N) . By contrast, at T > T (N) , the field-dependent magnetization curves behaved like a straight line. The H (c) is close to those obtained by previous spin resonance studies of Ni-5(TeO3)(4)Br-2 and Ni-5(TeO3)(4)Cl-2 in which a spin-flop-like transition was proposed to explain the field-dependent resonance spectra. Interestingly, the observed change in magnetization (Delta M) at H (c) corresponds to nearly one-half of the magnetic moment of Ni2+ ion, suggesting that the observed step-like behavior possibly corresponds to a spin-flip-like transition (i.e. from antiferromagnetic state to ferrimagnetic state). In addition, in the high-field region (H > H (c) ), the M(H) curves did not show plateau behavior, but exhibited the straight lines having finite slopes without any sign of saturation up to 55 T.