Diagonal static spin correlation in the low-temperature orthorhombic Pccn phase of La 1.55 Nd 0.4 Sr 0.05 CuO 4

Elastic neutron-scattering measurements have been performed on ${\mathrm{La}}_{1.55}{\mathrm{Nd}}_{0.4}{\mathrm{Sr}}_{0.05}{\mathrm{CuO}}_{4},$ which exhibits a structural phase transition at ${T}_{s}\ensuremath{\sim}60 \mathrm{K}$ from the low-temperature orthorhombic $\mathrm{Bmab}$ phase (labeled LTO1) to the low-temperature orthorhombic $\mathrm{Pccn}$ phase (labeled LTO2). At low temperatures, well below ${T}_{s},$ elastic magnetic peaks are observed at the ``diagonal'' incommensurate (IC) positions $(0,1\ifmmode\pm\else\textpm\fi{}0.055,0),$ with the modulation direction only along the orthorhombic b axis, just as in Nd-free ${\mathrm{La}}_{1.95}{\mathrm{Sr}}_{0.05}{\mathrm{CuO}}_{4}.$ In the present study, the one dimensionality of the IC modulation, which is naturally explained by a stripe model, is clearly demonstrated with our ``single-domain'' crystal. The temperature dependence of the IC peak intensity suggests a substantial contribution from the ${\mathrm{Nd}}^{3+}$ spins below $\ensuremath{\sim}3 \mathrm{K}.$ Consistent with this, the L dependence of the magnetic scattering is accurately accounted for by a model in which the contribution of the ${\mathrm{Nd}}^{3+}$ spins is explicitly included.