Magnetic characterization of undoped and 15%F doped LaFeAsO and SmFeAsO compounds

TL;DR

This study investigates the magnetic properties of undoped and fluorine-doped LaFeAsO and SmFeAsO compounds, revealing insights into their magnetic behavior, phase transitions, and coexistence of superconductivity and magnetism.

Contribution

The paper provides a detailed magnetic characterization of 1111 Fe-based superconductors, highlighting the effects of doping and impurity influences on magnetic and superconducting properties.

Findings

Identification of SDW onset and antiferromagnetic order in undoped samples

Observation of coexistence and competition between superconductivity and magnetic order in doped SmFeAsO

Estimation of Pauli susceptibility and Wilson ratio in the compounds

Abstract

In this paper the magnetic behaviour of undoped and 15% F doped SmFeAsO (Sm-1111) and LaFeAsO (La-1111) samples is presented and discussed. Magnetization measurements are not a simple tool to use for the characterisation of the new family of Fe-based superconductors because magnetic impurities can be easily formed during the preparation procedure and may affect the magnetic signal. In spite of this problem bulk magnetization measurements, properly treated, may give very useful information. In the undoped samples we gathered the main aspects of the physical behavior of the 1111 phase, i.e. the onset of the Spin Density Wave (SDW), the antiferromagnetic ordering at the Sm sublattice and the susceptibility increase with increasing temperature above the SDW temperature, and, in addition, we were able to estimate the Pauli contribution to susceptibility and therein the Wilson ratio both for LaFeAsO and SmFeAsO compounds, and the amplitude of the jump at the SDW temperature. In the doped samples, while the presence of magnetic signals due to impurities is dominating in the normal state, the superconducting behavior may be clearly observed and studied. In particular, in the Sm-1111 superconducting sample the coexistence-competition between superconductivity and antiferromagnetic ordering of the Sm ions was clearly observed.