Semiconducting ferromagnetic states in La1-xSr1+xCoO4

Electrical, magnetic, and structural properties have been investigated for single-layered (K2NiF4-type structure) compounds of La1-xSr1+xCoO4 (0 <= x <= 0.5) as the hole-doped system derived from the Mott insulator (x=0). The doping variations of the collective Jahn-Teller distortion and the effective magnetic moment indicate that the doped holes mostly enter the t(2g) orbital states with keeping the intermediate spin configuration. Anomalous Hall effect and intergrain tunneling magnetoresistance are observed as hallmarks of (semi-)conducting ferromagnets. Detailed comparison of temperature dependence of high- and low-field magnetizations suggests the presence of ferromagnetic cluster state (or Griffiths-type phase) as a consequence of the competition between the ferromagnetic and antiferromagnetic interaction under random potential.