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The temperature dependent local structure of TbMn 2 O 5 was determined by x-ray absorption spectroscopy.An anomalous Tb-O distribution is found. At high temperature it is broad but resolves into two distinct peaks below ~180 K. The distributions sharpen below the Tb magnetic ordering temperature (~10 K). The distortions in the Tb-O distribution, away from the Pbam structure, are consistent with rotations of the MnO x polyhedra about the c-axis and suggest that Tb-O bond polarization may play a significant role in the observed ferroelectric properties of this system.

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International audienc

A study of the properties of La 0.8 MnO 3 films of varying thickness was performed. Transport and magnetization measurements show that the ferromagnetic ͑metallic͒ volume fraction of the film varies from ϳ 1/4 for ultrathin 60 Å films to ϳ 1/2 for 1600 Å films. Multilength scale structural measurements reveal that near 300 Å, a transition from highly strained ultrathin films to relaxed bulk-like films occurs. The transition region is characterized by low surface roughness, high crystallite orientation, and broad d-spacing distributions.

Synchrotron infrared measurements were conducted over the range 100 to 8000 cm -1 on a self-doped La x MnO 3-δ (x~0.8) film. From these measurements we determined the conductivity, the effective number of free carriers, and the specific phonon modes as a function of frequency. While the metal-insulator transition temperature (T MI ) and the magnetic ordering temperature (T C ) approximately coincide, the free carrier density onset occurs at a significantly lower temperature (~45 K below). This suggests that local distortions exist below T MI and T C which trap the e g conduction electrons. These regions with local distortions constitute an insulating phase which persists for temperatures significantly below T MI and T C .The initial large drop in resistivity is due to the enhanced magnetic ordering while further drops correspond to reductions in the insulating phase which increase the number of free carriers. : 78.20.-e, 72.80.-r, 75.47.Lx, 64.75.St PACS Numbers

Mn K-edge resonant inelastic x-ray scattering measurements were performed on films of La0.8MnO3−δ. The measurements reveal that strain causes large shifts of the bands above the Fermi level. The Mn 3d band switches from a narrow upshifted peak at high temperature to a broad bulklike band at low temperature in ultrathin films. The strain induced switching behavior opens the possibility of tuning the transition to higher temperatures for device applications in this class of manganite materials.