Single-layered manganites of composition La1-xSr1+xMnO4 are reference materials of the colossal magneto-resistance manganites but exhibit similar effects only at extremely high magnetic fields of the order of 30T. But the system shows a series of interesting ordering phenomena as function of doping without a magnetic field. The x=0 compound containing only Mn3+ exhibits simple commensurate antiferromagnetic order combined with a strong octahedron distortion due to the Jahn-Teller effect. Minor amounts of holes lead to quasi‑localized magnetic excitations strongly coupled to the antiferromagnetic matrix. Strong structural changes are observed upon increase of the Sr-amount indicating that the eg-orbital occupation and the octahedron distortion flip into the planes. Around x=0.5, i.e. for equal amounts of Mn3+ and Mn4+, the so-called CE‑type order is observed. We have studied the magnetic excitations of this phase which are governed by a ferromagnetic interaction in-spite of its antiferromagnetic character. Furthermore we have analyzed the influence of the CE-type ordering on the lattice dynamics.
Universität zu Köln