Magnetic properties and Griffiths singularity in La0.45Sr0.55 Mn1−xCoxO3

The magnetic properties and the Griffiths singularity were investigated in Mn-site doped manganites of La0.45Sr0.55Mn1−xCoxO3 (x=0, 0.05, 0.10 and 0.15) in this work. The parent sample La0.45Sr0.55MnO3 undergoes a paramagnetic–ferromagnetic transition at TC=290 K and a ferromagnetic–antiferromagnetic transition at TN=191 K. The doping of Co ions enhances the ferromagnetism and suppresses the antiferromagnetism. The enhanced ferromagnetism results from the fact that the Co doping enhances the Mn3+–Mn4+ double-exchange interaction and induces the Co2+–Mn4+ ferromagnetic superexchange interaction. Detailed investigation on the magnetic behavior above TC exhibits that the Griffiths singularity takes place in this series of Mn-site doped compounds. The correlated disorder induced by the Co ionic doping, together with the phase competition from the ferromagnetic and the antiferromagnetic interactions among Mn ions, is responsible for the Griffiths singularity.