Magnetic properties of undoped and 15%F doped SmFeAsO compounds

TL;DR

This study investigates the magnetic properties of undoped and fluorine-doped SmFeAsO compounds, revealing antiferromagnetic ordering, coexistence with superconductivity, and Curie-Weiss behavior of Fe moments.

Contribution

It provides detailed magnetic characterization of SmFeAsO and SmFeAs(O0.85F0.15), highlighting the coexistence of magnetic orderings and superconductivity in doped samples.

Findings

Antiferromagnetic ordering of Fe moments at 140K in undoped SmFeAsO.

Superconductivity at 52K in fluorine-doped SmFeAs(O0.85F0.15).

Coexistence of magnetic order and superconductivity in doped samples.

Abstract

In this paper the magnetic behaviour of SmFeAsO and SmFeAs(O0.85F0.15) samples is presented and discussed. Molar susceptibility of SmFeAsO exhibits a local peak at T around 140K due to the establishment of a long range antiferromagnetic ordering of the Fe moments in Fe-As layers. This feature has already been observed with different techniques, and frequently ascribed to the onset of a Spin Density Wave (SDW). At TN around 6K another peak, which we attribute to the establishment of antiferromagnetic ordering of Sm ion sublattice, is observed. Furthermore, a temperature independent signal (Pauli paramagnetism, Landau and core diamagnetism...) is also present in the magnetic behaviour of this sample. In SmFeAs(O0.85F0.15) the antiferromagnetic ordering in Fe-As plane is suppressed and superconductivity occurs at T = 52 K, whereas the antiferromagnetic ordering of Sm ions at low temperature persists, leading to the coexistence and competition between superconducting and magnetic orderings. Above the transition temperature, after the subtraction of the Sm ion sublattice paramagnetic contribution and of the temperature independent contribution to the experimental susceptibility data, a Curie-Weiss behaviour for Fe is observed, with a magnetic moment of 1.4 Bohr magneton.