High-Field Magnetization of the Distorted Spin Frustration System Ni5(TeO3)4Br2.

We performed high-field magnetization measurements, M( H), on the Ni₅(TeO₃)₄Br₂ 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∼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∼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 Ni₅(TeO₃)₄Br₂ and Ni₅(TeO₃)₄Cl₂ in which a spin-flop-like transition was proposed to explain the field-dependent resonance spectra. Interestingly, the observed change in magnetization (Δ 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. [ABSTRACT FROM AUTHOR]