A Study of Structural and Magnetic Properties of Superconducting FeTeO(x)/Non Superconducting FeTe Film System

This work describes the synthesis methods to optimize the quality and stability of FeTeOx/FeTe thin films and characterization of the low temperature crystal and magnetic structure of superconducting FeTeOx/non-superconducting FeTe film system. Iron based superconductors have reinvigorated studies of high temperature superconductivity since their discovery in 2008. The 11 family of superconductors are the simplest among Fe-based compounds. FeTe, which is non-superconducting and magnetic, is considered the parent compound for this family. FeTe can be made superconducting by incorporating interstitial oxygen. In this work, an extensive study has been done to explore the effect of growth parameters for the pulsed laser deposition technique on FeTeOx film growth. A new growth mode has been introduced to produce films with stable oxygen concentration and better crystalline quality. High-resolution synchrotron x-ray diffraction was used to study the low temperature crystal structure of superconducting FeTeOx. We found that superconducting FeTeOx undergoes a structural transition from tetragonal to monoclinic similar to the parent FeTe but no change could be detected in the crystal symmetry of FeTeOx in the superconducting state compared to its normal state. An anomaly in the c-axis lattice parameter was observed at the vicinity of the superconducting transition. Using the Ehrenfest relation and above anomaly we predicted a large enhancement of Tc in strained FeTeOx films. Low temperature neutron diffraction and Mossbauer spectroscopy reveal that superconducting FeTeOx films order aniferromagnetically around 65 K similar to parent FeTe and suggest a suppression of magnetism upon entering the superconducting state