Magnetic and structural transitions in La$_{0.4}$Na$_{0.6}$Fe$_2$As$_2$ single crystals

TL;DR

This study investigates the structural and magnetic phase transitions in La$_{0.4}$Na$_{0.6}$Fe$_2$As$_2$ single crystals, revealing a coupled structural and magnetic transition at 125 K and providing a new platform for exploring iron-based superconductors.

Contribution

The paper reports the synthesis and detailed characterization of La$_{0.4}$Na$_{0.6}$Fe$_2$As$_2$ single crystals, highlighting their structural and magnetic transitions, and introduces this material as a new platform for studying electron-hole asymmetry in iron-based superconductors.

Findings

Structural transition at 125 K from tetragonal to orthorhombic phase.

Fe moments order along the a direction with 0.7 μ_B at 5 K.

Stripe antiferromagnetic structure similar to other AFe2As2 compounds.

Abstract

La$_{0.4}$Na$_{0.6}$Fe$_2$As$_2$ single crystals have been grown out of an NaAs flux in an alumina crucible and characterized by measuring magnetic susceptibility, electrical resistivity, specific heat, as well as single crystal x-ray and neutron diffraction. La$_{0.4}$Na$_{0.6}$Fe$_2$As$_2$ single crystals show a structural phase transition from a high temperature tetragonal phase to a low-temperature orthorhombic phase at T$_s$\,=\,125\,K. This structural transition is accompanied by an anomaly in the temperature dependence of electrical resistivity, anisotropic magnetic susceptibility, and specific heat. Concomitant with the structural phase transition, the Fe moments order along the \emph{a} direction with an ordered moment of 0.7(1)\,$\mu_{\textup{B}}$ at \emph{T}\,=\,5 K. The low temperature stripe antiferromagnetic structure is the same as that in other \emph{A}Fe$_{2}$As$_{2}$ (\emph{A}\,=\,Ca, Sr, Ba) compounds. La$_{0.5-x}$Na$_{0.5+x}$Fe$_2$As$_2$ provides a new material platform for the study of iron-based superconductors where the electron-hole asymmetry could be studied by simply varying La/Na ratio.