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 Y1-xCaxBa2Cu3O6. Samples with carrier densities p(sh) = 0.015-0.035 (x = 0.03-0.07) were studied in the temperature range 2.6-200 K using the zero-field time differential muon spin rotation (ZF TD mu SR) technique. An oscillating 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 frequency diminished slightly with increasing Ca concentration. Two distinct regimes of frequency as a function of temperature are separated by a kink, which is interpreted as an independent ordering of the spins of the doped holes. The doped-hole spin-freezing temperature is doping dependent and occurs 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-glass mechanism through calcium doping. Apparent transitions between the 3D frozen-hole antiferromagnetic state and the spin-glassy state with diffusing 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) 1999 Elsevier Science B.V. All rights reserved.