Ni Impurity Effect on Antiferromagnetic Order in Hole-doped La2-xSrxCuO4

Abstract

The doping effect of magnetic impurities on the lightly hole-doped antiferromagnetic state was investigated by neutron diffraction techniques using single crystals of La 1.99 Sr 0.01 Cu 1- y Ni y O 4 (0.01≤ y ≤0.10). Dilute Ni-doping between y =0.02 and 0.05 dramatically changes the Q -dependence of the antiferromagnetic Bragg intensity, corresponding to a switch of spin structure from the La 2 CuO 4 type (Cu type) to the La 2 NiO 4 type (Ni type) triggered by a spin rotation in CuO 2 planes. Upon Ni-doping, the Neel temperature ( T N ) increases and rapidly approaches that of nondoped La 2 CuO 4 in the Cu-type phase due to the strong localization of doped carriers, whereas T N gradually decreases in the Ni-type phase. More interestingly, between the Cu- and Ni-type structures, there exists an intermediate region where the spin direction is between those of Cu- and Ni-types. In this region, we found an unusual temperature dependence of magnetic intensities, which suggests a temperature dependence of the s...