Suppression of Antiferromagnetic Order by Light Hole Doping in   La_2Cu_{1-x}Li_xO_4: A ^{139}La NQR Study
  ^{139}La nuclear quadrupole resonance measurements in lightly doped La_2Cu_{1-x}Li_xO_4 have been performed to reveal the dependence of the magnetic properties of the antiferromagnetic CuO_2 planes on the character of the doped holes and their interactions with the dopant. A detailed study shows that the magnetic properties are remarkably insensitive to the character of the dopant impurity. This indicates that the added holes form previously unrecognized collective structures. 
B. J. Suh, Y. Yoshinari, J. D. Thompson, P. C. Hammel, J. L. Sarrao,   and Z. Fisk