Magnetic properties for the one-dimensional multicomponent quantum spin system with the excitation gap are studied based on the integrable spin model introduced by Bariev et al. By exactly computing the magnetization, we show how the characteristic structure with plateaus and cusps appears in the magnetization process. To study low-energy dynamics of the system, we apply the finite-size scaling analysis to the excitation spectrum, and thereby evaluate the power-law exponent as well as the

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... ement factor for the low-temperature NMR relaxation rate 1/T_1. We discuss the critical properties of 1/T_1 around plateaus and cusps in the magnetization curve.