57-Fe Mossbauer study of magnetic ordering in superconducting K_0.85Fe_1.83Se_2.09 single crystals

TL;DR

This study uses 57-Fe Mossbauer spectroscopy to investigate magnetic ordering in superconducting K_0.85Fe_1.83Se_2.09 crystals, revealing persistent magnetic order coexisting with superconductivity and a possible first-order magnetic transition.

Contribution

It provides detailed insights into the magnetic behavior of K_0.85Fe_1.83Se_2.09, highlighting the coexistence of magnetism and superconductivity and suggesting a first-order magnetic transition.

Findings

Magnetic order persists below T_sc and up to T_N=532K.

Iron moments are aligned perpendicular to the crystal plates.

Magnetic order collapses rapidly above 500K, indicating a possible first-order transition.

Abstract

The magnetic ordering of superconducting single crystals of K_0.85Fe_1.83Se_2.09 has been studied between 10K and 550K using 57-Fe Mossbauer spectroscopy. Despite being superconducting below T_sc ~30K, the iron sublattice in K_0.85Fe_1.83Se_2.09 clearly exhibits magnetic order from well below T_sc to its N\'eel temperature of T_N = 532 +/- 2K. The iron moments are ordered perpendicular to the single crystal plates, i.e. parallel to the crystal c-axis. The order collapses rapidly above 500K and the accompanying growth of a paramagnetic component suggests that the magnetic transition may be first order, which may explain the unusual temperature dependence reported in recent neutron diffraction studies.