Muon-spin-relaxation and neutron-scattering studies of magnetism in single-crystal La1.94Sr0.06CuO4

Abstract

Combined muon-spin-relaxation (${\mathrm{\mu }}^{+}$SR) and elastic magnetic neutron-scattering experiments on a large single crystal of ${\mathrm{La}}_{1.94}$ ${\mathrm{Sr}}_{0.06}$ ${\mathrm{CuO}}_4$ are reported. ${\mathrm{\mu }}^{+}$SR data taken without an external field indicate that the Cu spins are fluctuating slowly or frozen below ${\mathit{T}}_{\mathit{f}}^{\mathrm{\mu }}$≊6.0 K. At 3.9 K, measurements done with an applied longitudinal field show that the muon depolarization is almost completely due to static moments. Neutron measurements of the magnetic peaks Q=(1,0,0) and (0,1,1) show that no three-dimensional long-range order is present down to 1.8 K. However, the quasielastic scattering intensity from the two-dimensional ridge Q=(1,k,0) at k=-0.12 increases sharply between 40 and 20 K. Below ${\mathit{T}}_{\mathit{f}}^{\mathit{N}}$=20 K the scattering intensity is roughly constant. The difference between these two freezing temperatures is explained in terms of the different range of fluctuation frequencies to which each of these probes is sensitive. The dependence of the freezing temperature on the frequency windows of different probes is similar to that seen in traditional spin-glass materials like CuMn.