Temperature-dependent evolution of the electronic and local atomic structure in the cubic colossal magnetoresistive manganite La1-x Srx Mn O3

Abstract

We have studied the temperature-dependent evolution of the electronic and local atomic structure in the cubic colossal magnetoresistive manganite La1-x Srx Mn O3 (x=0.3-0.4) with core and valence level photoemission (PE), x-ray absorption spectroscopy (XAS), x-ray emission spectroscopy (XES), resonant inelastic x-ray scattering (RIXS), extended x-ray absorption fine structure (EXAFS) spectroscopy, and magnetometry. As the temperature is varied across the Curie temperature TC, our PE experiments reveal a dramatic change of the electronic structure involving an increase in the Mn spin moment from ≈3 μB to ≈4 μB, and a modification of the local chemical environment of the other constituent atoms, indicative of electron localization on the Mn atom. These effects are reversible and exhibit a slow-time scale, with an ≈200-K -wide hysteresis centered at TC. Based on the probing depths accessed in our PE measurements, these effects seem to survive for at least 35-50 Å inward from the surface, while other consistent signatures for this modification of the electronic structure are revealed by more bulk-sensitive spectroscopies such as XAS and XES/RIXS. We interpret these effects as spectroscopic fingerprints for polaron formation, associated with the presence of local Jahn-Teller distortions of the Mn O6 octahedra around the Mn atom, as revealed by the EXAFS data. Magnetic susceptibility measurements, in addition, show typical signatures of ferromagnetic-cluster formation well above the Curie temperature. © 2008 The American Physical Society.