Percolative conductivity and superconductivity in La1.85−xSr0.15+xCu1−xMnxO4

The effects of Mn substitution for Cu on conductivity and magnetism in La1.85−xSr0.15+xCu1−xMnxO4 have been investigated by electric resistivity, dc magnetic susceptibility, and electron spin resonance measurements. Superconductivity with x up to 0.1 was observed. Variable range hoping transport due to the random potential introduced by Mn doping was suggested. Sudden decrease in resistivity for x > 0.34 is related to the formation of Mn-O-Mn percolative conducting channel. The occurrence of ferromagnetism and antiferromagnetism for x ⩾ 0.2 is understood based on the discussion about the variation of valent state of Mn.