Effects Of Reduced Dimensionality On Spin Dynamics In The Layered Perovskite La1.4sr1.6mn2o7

We report zero-field muon spin rotation data in single crystals of La1.4Sr1.6Mn2O7 for T = 5-325 K. The spin-lattice relaxation rate is spatially inhomogeneous below the 3D magnetic transition temperature T-C and anisotropic above T-C. We find evidence against 2D spin ordering or in-plane correlations above T-C. Additionally, the very slow spin fluctuations found below T-C in cubic (3D) perovskites like (La, Ca)MnO3 or (La, Sr)MnO3, and attributed to relatively small magnetoelastic polarons, are absent in La1.4Sr1.6Mn2O7. This suggests that the polaron size in the layered material is significantly larger than in the 3D perovskites. [S0031-9007(98)06898-7].