Optical indication of metallic clusters in the layered manganites La _{2 − 2 x} Sr _{1 + 2 x} Mn ₂ O ₇ above T _C

Abstract

Optical absorption in the bi-layered manganites La2−2x Sr1+2x Mn2O7 (x = 0.3 and 0.4) was studied and metallic clusters were revealed in the temperature range TC < T < 270 K in the composition with x = 0.4. The existence of metal clusters is considered as the principal cause of magnetoresistance, the tails of magnetization and ferromagnetic correlations, which are observed in this manganite up to temperatures several times exceeding the temperature TC of 3D magnetic ordering.