2005 Volume 74 Issue 8 Pages 2197-2200
The doping effect of magnetic impurities on the lightly hole-doped antiferromagnetic state was investigated by neutron diffraction techniques using single crystals of La1.99Sr0.01Cu1−yNiyO4 (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 La2CuO4 type (Cu type) to the La2NiO4 type (Ni type) triggered by a spin rotation in CuO2 planes. Upon Ni-doping, the Néel temperature (TN) increases and rapidly approaches that of nondoped La2CuO4 in the Cu-type phase due to the strong localization of doped carriers, whereas TN 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 spin direction. These unusual behaviors are discussed in terms of doped carrier itinerancy.
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