Cu-NMR study in the field up to 30 T has been performed on the two-legged quantum spin ladder system NH4CuCl3 which shows the two-stepped plateaus in magnetization. By analyzing the angular dependence of the peak shift, observed Cu-NMR spectra are assigned to the singlet site with a very small magnetic shift. The temperature dependence of this shift does not reflect that of the macroscopic magnetization, indicating that the excited triplet sites in NH4CuCl3 have a tendency to be immobile at low temperatures.
- Magnetization plateau
- Quantum spin ladder