Abstract

We have measured the muon-spin relaxation (µSR) in La_0.6Sr_0.4MnO₃ and in its layered sister system La_1.2Sr_1.8Mn₂O₇ to study the influence of dimensionality on their magnetic properties. Both compounds show ferromagnetic ordering with decreasing temperature. Above their Curie temperatures we followed the spin fluctuations. While the electron spin fluctuations in the three-dimensional La_0.6Sr_0.4MnO₃ slow down critically as the transition temperature is approached they remain finite in the layered material La_1.2Sr_1.8Mn₂O₇. We can fit them to 2D critical behaviour with a lower T_C. In addition, we observe a spin precession signal in the ferromagnetically ordered state in La_1.2Sr_1.8Mn₂O₇; the temperature dependence of the muon precession frequency is in agreement with a three-dimensional character of the ordering.

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