^<139>La NQR Study of the Magnetic Properties of La_<2-x>M_xCuO_4 (M=Ba, Sr) for 0≦x≦0.08

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The magnetic properties of La_<2-x>M_xCuO_4 (M=Ba, Sr) for 0≤x≤0.08 have been investigated from 1.5 K to 300 K by the nuclear quadrupole resonance (NQR) of ^<139>La (I=7/2). The electrical quadrupole relaxation process of ^<139>La in La_2CuO_4 is dominant above 50 K in spite of the existence of the internal field at the La site due to the antiferromagnetic ordering of Cu-moments. At low temperature, the magnetic relaxation process becomes dominant. From the divergence of the nuclear relaxation rate, T^<-1>_1, of ^<139>La, we obtain the magnetic phase diagram which consists of two distinct magnetic phases for 0<x<0.05. The internal field at the La-site changes discontinuously at T^*_c at which the temperature dependence of T^<-1>_1 shows a peak. This change can be interpreted by decrease of the transferred hyperfine fields from Cu spins through the apical oxygen of the CuO_6 octahedron below T^*_c.
社団法人日本物理学会の論文
1994-04-15