Antiferromagnet (Ln,Ca)CuO2.5 near the quantum critical point (Ln = Pr,Nd)

The Neel temperatures T-N of two-leg ladder compounds LnCuO(2.5) (Ln: Pr, N d) kin to LaCuO2.5 were determined by zero-field muon spin precession. It w as found that T-N = 17 K in PrCuO2.5 and 1.8 K in NdCuO2.5, which are both considerably reduced from T-N = 125 K in LaCuO2.5. No spin precession signa l was observed in Nd0.68Ca0.35CuO2.5. These results demonstrate that the sp in-ladder system approaches the quantum critical point by substituting Pr o r Nd for La, and that the Neel order of these compounds is completely destr oyed upon Ca doping. (C) 2000 Elsevier Science B.V. All rights reserved.