Zero-field muon-spin-rotation study of hole antiferromagnetism in low-carrier-density Y1-xCaxBa2Cu3O6

We have studied magnetic correlations in the low-carrier-doping regime of Y 1-xCaxBa2Cu3O6. Samples with carrier densities p(sh) = 0.015-0.035 (x = 0.0 3-0.07) were studied in the temperature range 2.6-200 K using the zero-fiel d time differential muon spin rotation (ZF TD mu SR) technique. An oscillat ing signal, of 4.1 MHz (similar to 300 G) in the low-temperature limit (T-- > 0 K), indicative of antiferromagnetism was found in each sample. This fre quency diminished slightly with increasing Ca concentration. Two distinct r egimes of frequency as a function of temperature are separated by a kink, w hich is interpreted as an independent ordering of the spins of the doped ho les. The doped-hole spin-freezing temperature is doping dependent and occur s in the range 20.8-33 K. Even in the low-carrier-density regime, the long- range antiferromagnetic ordering is still strongly frustrated by the spin-g lass mechanism through calcium doping. Apparent transitions between the 3D frozen-hole antiferromagnetic state and the spin-glassy state with diffusin g holes were observed. Clearly the same magnetic interaction mechanisms are operating in both low-carrier-density (Y,Ca)-123 and (La,Sr)(2)CuO4. (C) 1 999 Elsevier Science B.V. All rights reserved.