Abstract
In (La 1- x Ba x ) 2 CuO 4 , the Cu-NQR spectra for x =0.0625 and x =0.08 were observed in each phase of the crystal structure. The temperature dependence of the spin echo decay rate, T 2 -1 , was also measured from 1.5 K to 300 K for both samples. The two well-separated sets of NQR spectra were observed in the high-temperature tetragonal (HTT) and low-temperature orthorhombic (LTO) phases in both samples. The spectrum at 1.5 K in the low-temperature tetragonal (LTT) phase for x =0.0625 is abnormally broadened compared to the spectra in the HTT and LTO phases, and T 2 -1 shows strong divergence at about 35 K. These two abnormal static and dynamical results indicate that the electronic state of the Cu atom changes from a nonmagnetic to magnetic one in the LTO → LTT transition, and some magnetic phase transition occurs at about 35 K which is lower than the LTT transition temperature, 60 K.
Published Version
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