Non-conventional magnetic order in Fe-substituted La_0.7Sr_0.3MnO₃giant-magnetoresistance manganites

Abstract

Magnetization measurements and Mössbauer spectrometry have been performed on La0.7Sr0.3Mn1−xFexO3 (x = 0.01, 0.05, 0.1, 0.2, 0.30), to clarify the local magnetic order around Fe3+ ions. As Mn atoms are substituted for with Fe, the magnetic structure dramatically changes, because the ferromagnetic double-exchange chain is broken. At 4.2 K all compounds are magnetically ordered with large hyperfine fields. For x = 0.05 ferromagnetic and paramagnetic phases coexist over a large temperature range. Magnetic ordering occurs in a double step. Superparamagnetic effects are observed, and can explain part of this atypical ordering process, but there is evidence of segregation and clustering of Fe, even at this low concentration.