Doping effect on magnetic and transport properties of Pr _2-xSr_xCoO₄

We present the results of a systematic investigation of the dc magnetization, ac susceptibility, resistivity and thermopower of Pr _2-xSr_xCoO₄ (x = 1.2, 1.3 and 1.5). The x = 1.2 specimen undergoes a paramagnetic phase above 201.57K, Griffiths phase between 201.57 and 129.24K, ferromagnetic cluster-glass phase between 129.24 and 16.19K and spin-glass state reentrance below 16.19K. With increasing Sr content, the Griffiths phase and the spin-glass state are suppressed. The specimen shows a p-type semiconducting conduction changing from thermally activated conduction to variable range hopping conduction with increasing Sr doping level. The rich magnetic and transport behaviors are suggested due to the complicated magnetic interactions and Jahn-Teller distortion of the cobalt ions associated with small polarons.