μsR and thermal conductivity studies on inhomogeneity of the impurity- and field-induced magnetism and superconductivity in high-T_c cuprates

The inhomogeneity of the impurity- and field-induced magnetic order and superconductivity has been investigated in the hole-doped La _2-xSr_xCuO₄ (LSCO), La_2-xBa _xCuO₄ (LBCO) and the electron-doped Pr _1-xLaCe_xCuO₄ (PLCCO). For the hole-doped cuprates, it has been found from the muon-spin-relaxation measurements that both Zn and Ni impurities tend to develop a magnetic order and to destroy the superconductivity around themselves not only around p (the hole concentration per Cu) = 1/8 but also at x = 0.15 and 0.18 in LSCO, though the development of the magnetic order by Zn is more marked than by Ni. Moreover, it has been found from the thermal conductivity measurements that the development of the magnetic order by the application of magnetic field is marked not just at p = 1/8 but in the neighborhood of p = 1/8 in LSCO and LBCO. The impurity- and field-induced magnetic order in the hole-doped cuprates can be interpreted as being due to pinning of the dynamical stripes of holes and spins by impurities and vortex cores in the CuO₂ plane, respectively. For the electron-doped PLCCO with x = 0.14, on the contrary, no impurity-induced magnetic order has been observed. The reason is discussed.