Spin reorientation and glassy dynamics inLa1.55Sr0.45NiO4

Abstract

The magnetism of charge-stripe-ordered ${\text{La}}_{1.55}{\text{Sr}}_{0.45}{\text{NiO}}_{4}$ was studied by a combination of neutron diffraction, muon-spin relaxation $(\ensuremath{\mu}\text{SR})$, and bulk susceptibility. Long-range magnetic ordering was observed at a lower temperature by $\ensuremath{\mu}\text{SR}$ than by neutron diffraction, consistent with a glassy transition to the ordered phase. A second magnetic transition is detected by all techniques and is consistent with a spin reorientation. On cooling below ${T}_{\text{SR}}=42\text{ }\text{K}$ the spins reorientate from lying $32.9\ifmmode\pm\else\textpm\fi{}0.6\ifmmode^\circ\else\textdegree\fi{}$ away from the stripe direction at 70 K to $56.8\ifmmode\pm\else\textpm\fi{}0.4\ifmmode^\circ\else\textdegree\fi{}$ at 10 K. The magnetic order was observed by neutron diffraction to have both three-dimensional and two-dimensional (without any correlation along the $c$ axis) characters. $\ensuremath{\mu}\text{SR}$ measurements confirmed this and are consistent with a single magnetically ordered spin-stripe phase. The effects of checkerboard charge order on the ordered phase and the characteristics of the phase diagram of the spin reorientation in charge-ordered ${\text{La}}_{2\ensuremath{-}x}{\text{Sr}}_{x}{\text{NiO}}_{4}$ are commented on.