High-field magnetization studies of spin-dimer behaviors on low-dimensional spin systems, LiCu$_{2-x}$Zn$_{x}$O$_{2}$ and FeTe$_{3}$O$_{7}$X (X = Cl, Br)

High-field magnetization of two kinds of low-dimensional spin system was studied in pulsed magnets. Several anomalies were clearly observed in dm/dH curves of doped LiCu$_{2-x}$Zn$_{x}$O$_{2}$ (x = 0.07) at low temperatures (1.3 K $<$ $T$ $<$ 20 K). When temperature decreases, the anomalies sharper / splits at certain critical temperatures which are related to the formation of isolated spin-dimer and spin freezing state. A field-induced spin density wave state was suggested to exist at high magnetic fields. The doping of Zn$^{2+}$ ions breaks the spin-chain of Cu$^{2+}$ ions, leading to the formation of isolated spin-dimers and lowering the critical field of formation of spin density state. The magnetization process measurements were preformed on another series of samples, FeTe$_{3}$O$_{7}$X (X = Cl, Br), which has spin-dimer, formed by Fe$^{3+}$ ions, at low temperatures and magnetic fields up to 100 T. At low temperatures, the magnetization processes show four step-like structures, which have nearly equal spaces of 25 T. Both samples show similar behavior. These steps are considered to be the magnetic excitation of the antiferromagnetic spin-dimers.