MU+SR STUDY OF MAGNETIC ORDER IN LA2NIO4+DELTA

Increasing attention has been devoted lately to the La2NiO4-type oxides due to the similarities with the superconducting copper oxides. In this work we report a microscopical study of the magnetic ordering in La2NiO4+delta by using mu+SR. The coherent spin precession of implanted muons due to internal fields in the ordered state, has been detected in three La2NiO4+delta polycrystalline samples. Long range order was apparent only in stoichiometric La2NiO4, for which T(N) almost-equal-to 320 K and the first order orthorhombic-to-tetragonal structural phase transition was detected as a gradual increase with decreasing temperature of the precession frequency of the implanted muons bound to apical oxygens. A strongly damped oscillating signal could be detected only at the lowest temperature (5 K) for the non-stoichiometric (oxidized) samples which evidences a highly disordered magnetic state.