Effects of Ga doping on the magnetic ordering of Pr in PrBa ₂Cu₃O₇

Neutron-diffraction and ac-susceptibility measurements have been performed to study the effects of Ga doping on the magnetic ordering of the Pr in PrBa₂(Cu_1-xGa_x)₃O₇. The Ga atoms preferentially replace the Cu atoms in the CuO-chain layers, and this substitution is found to decrease the antiferromagnetic ordering temperature as the Ga concentration is increased. In addition, the spin arrangement along the c axis is found to change from nearest neighbors being antiparallel for x=0 to nearest neighbors being parallel for x=0.08 (24% Cu chain substitution); for an intermediate x of 0.04 a mixture of the two spin structures is observed. The susceptibility results exhibit Curie-Weiss behavior above T_N, and departures from this behavior in the ordered state.