Commensurate Spin Density Wave in LaOFeAs: A Local Probe Study

TL;DR

This study investigates the magnetic order in LaOFeAs using local probes, revealing a commensurate spin density wave with a reduced magnetic moment and providing insights into its temperature dependence and theoretical modeling.

Contribution

It provides detailed local probe measurements of magnetic order in LaOFeAs, demonstrating a commensurate SDW with a reduced magnetic moment and comparing results to theoretical models.

Findings

Confirmed commensurate static magnetic order below 138 K

Measured a reduced magnetic moment of approximately 0.25 μ_B

Matched experimental data with a four-band SDW theoretical model

Abstract

We present a detailed study on the magnetic order in the undoped mother compound LaOFeAs of the recently discovered Fe-based superconductor LaO$_{1-x}$F$_x$FeAs. In particular, we present local probe measurements of the magnetic properties of LaOFeAs by means of $^{57}$Fe M\"ossbauer spectroscopy and muon spin relaxation in zero external field along with magnetization and resistivity studies. These experiments prove a commensurate static magnetic order with a strongly reduced ordered moment of 0.25(5) $\mu_B$ at the iron site below T_N = 138 K, well separated from a structural phase transition at T_N = 156 K. The temperature dependence of the sublattice magnetization is determined and compared to theory. Using a four-band spin density wave model both, the size of the order parameter and the quick saturation below T_N are reproduced.