We applied the high-field technique to study the magnetization process in model substances. Measurements have been performed on the powder samples under a pulsed magnetic field up to 50 T, A family of organic verdazyl radical is a candidate of an isotropic S = 1/2 antiferromagnetic linear chain model, The observed magnetization is practically zero up to a certain critical field around 40 T and steeply increases to the saturation value of 1 mu(B)/molecule. The feature cannot be explained by the uniform chain model but agrees with the alternation linear chain model closed to the dimer model in which the ground state is a nonmagnetic singlet with an energy gap between the excited triplet state. Metal-assembled tetranuclear complexes [Mn(MeOH)L(OH)M(bpy)](2) represent a prototype of geometrically frustrated spin systems. We observed a step-like magnetization process which clearly shows the successive transitions among quantum states with different total spins.