Muon-spin-rotation study of magnetism in La1.85Sr0.15CuO4 and YBa2Cu3Ox below 90 mK

Internal magnetic fields in YBa2Cu3Ox and La1.85Sr0.15CuO4 have been investigated below 90 mK using muon spin rotation. In YBa2Cu3Ox the static internal magnetic field at the muon site due to magnetic ordering remains constant with increasing x up until x=6.30 and then rapidly approaches zero just above x=6.44. In heavily doped samples of YBa2Cu3Ox (x≥6.54, Tc≥52 K) and La2-ySryCuO4 (y=0.15, Tc=37 K) we find little evidence for static or slowly fluctuating electronic moments. These results clearly establish that static magnetic order is destroyed in regions of high carrier concentration.