57Fe Mossbauer spectroscopy and magnetic measurements of oxygen deficient LaFeAsO

TL;DR

This study investigates the magnetic properties and oxygen vacancy effects in LaFeAsO1-x, revealing a crossover between magnetism and superconductivity with detailed Mossbauer spectroscopy and magnetic measurements.

Contribution

It provides detailed Mossbauer spectroscopy analysis of oxygen vacancies in LaFeAsO1-x, linking vacancy concentration to magnetic and superconducting crossover behavior.

Findings

Oxygen vacancy concentration estimated at 7.0%

Spectroscopy indicates coexistence of magnetic and non-magnetic Fe sites

LaFeAsO0.93 is a crossover compound between magnetism and superconductivity

Abstract

We report on the magnetic behavior of oxygen deficient LaFeAsO1-x (x-0.10) compound, prepared by one-step synthesis, which crystallizes in the tetragonal (S.G. P4/nmm) structure at room temperature. Resistivity measurements show a strong anomaly near 150 K, which is ascribed to the spin density wave (SDW) instability. On the other hand, dc magnetization data shows paramagnetic-like features down to 5 K, with an effective moment of 0.83 mB/Fe. 57Fe Mossbauer studies (MS) have been performed at 95 and 200 K. The spectra at both temperatures are composed of two sub-spectra. At 200 K the major one (88%), is almost a singlet, and corresponds to those Fe nuclei, which have two oxygen ions in their close vicinity. The minor one, with a large quadrupole splitting, corresponds to Fe nuclei, which have vacancies in their immediate neighborhood. The spectrum at 95 K, exhibits a broadened magnetic split major (84%) sub-spectrum and a very small magnetic splitting in the minor subspectrum. The relative intensities of the subspectra facilitate in estimating the actual amount of oxygen vacancies in the compound to be 7.0(5)%, instead of the nominal LaFeAsO0.90. These results, when compared with reported 57Fe MS of non-superconducting LaFeAsO and superconducting LaFeAsO0.9F0.1, confirm that the studied LaFeAsO0.93 is a superconductivity-magnetism crossover compound of the newly discovered Fe based superconducting family.