Spin-glass behavior in Ni-doped La1:85Sr0:15CuO4
  The dynamic and static magnetic properties of La1:85Sr0:15Cu1-yNiyO4 with Ni concentration up to y=0.63 are reported. All the features that characterize the spin-glass (SG) behavior are found: bifurcation of the dc susceptibility chi vs temperature curve, a peak in the zero-field cooling branch of this curve accompanied by a step in the imaginary part of the ac susceptibility chi_ac, frequency dependence of the peak position in the real part of chi_ac and scaling behavior. The decay of remnant magnetization is described by a stretched-exponential function. The characteristic time from the critical slowing-down formula that governs the dynamics of the system suggests the existence of the spin clusters. The strongest interactions between the fluctuating entities are at y equal to the charge carriers concentration in the system. The SG transition temperature decreases linearly with decreasing y for y<0.30 and extrapolates to 0 K at y=0 what means that Ni display a magnetic character in the surrounding Cu-O network starting from the smallest concentration y. The static critical exponents characterizing the scaling behavior of the nonlinear part of chi lie between those typical for three dimensional Ising-like and Heisenberg-like systems 
A. Malinowski, V. L. Bezusyy, R. Minikayev, P. Dziawa, Y. Syryanyy,   and M. Sawicki
cond-mat.supr-con