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

Abstract

Internal magnetic fields in ${\mathrm{YBa}}_2$ ${\mathrm{Cu}}_3$ ${\mathrm{O}}_{\mathrm{x}}$ and ${\mathrm{La}}_{1.85}$ ${\mathrm{Sr}}_{0.15}$ ${\mathrm{CuO}}_4$ have been investigated below 90 mK using muon spin rotation. In ${\mathrm{YBa}}_2$ ${\mathrm{Cu}}_3$ ${\mathrm{O}}_{\mathrm{x}}$ 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 ${\mathrm{YBa}}_2$ ${\mathrm{Cu}}_3$ ${\mathrm{O}}_{\mathrm{x}}$ (x≥6.54, $T_c$≥52 K) and ${\mathrm{La}}_{2\mathrm{-}\mathrm{y}}$ ${\mathrm{Sr}}_{\mathrm{y}}$ ${\mathrm{CuO}}_4$ (y=0.15, $T_c$=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.