High-field magnetization of a two-dimensional spin frustration system, Ni-5(TeO3)(4)X-2 (X = Br, Cl)

The high-field magnetization, M(H), of Ni-5(TeO3)(4)X-2 (X = Br, Cl) was measured by using a pulse magnet. These compounds have a two-dimensional crystal structure and a distorted Kagome spin frustrated system which is built from the Ni2+ ions (S = 1). The Neel transition temperatures are T-N similar to 28 and 23 K for X = Br and Cl, respectively. When T < T-N, we observe step-like transitions, at H-c similar to 11 and 10 T for X = Br and Cl, respectively. On the other hand, for T > T-N, the field-dependent magnetization curves behave like a monotonically increasing straight line up to 55 T. The H-c value is close to those obtained in previous spin resonance studies in which a model of a spin-flop scenario was proposed to explain the field-dependent resonance spectra. With the earlier model a further transition at around 23 T was predicted; however, our observations did not show any plateau behaviors, saturation or other anomalies up to 55 T, suggesting that the further transition possibly exists in a much higher field region.