Freezing of spin and charge inLa2−xSrxCuO4

Abstract

Zero- and longitudinal-field muon-spin relaxation ${\mu }^{+}\mathrm{SR}$ measurements have been performed on ${\mathrm{La}}_{2-x}{\mathrm{Sr}}_x\mathrm{Cu}{\mathrm{O}}_4$ alloys in both single-crystal and sintered powder forms above and below their magnetic transition temperatures, $T_f$. The ${\mu }^{+}$ precession frequency $v$ depends only weakly on $x$ and $T_f$, an observation which together with resistivity data implies classical freezing of magnetic moments in the regime where the carriers are localized. For $x=0.05\mathrm{}$, critical dynamics are observed near $T_f$. The ${\mu }^{+}\mathrm{SR}$ technique is shown to be very sensitive to ferromagnetically aligned pairs of ${\mathrm{Cu}}^{2+}$ moments; the population of such pairs increases greatly with $x$.