A 57Fe Moessbauer Spectroscopy Study of the 7 K Superconductor LaFePO

TL;DR

This study investigates the superconducting properties and local magnetic environment of LaFePO using 57Fe Moessbauer spectroscopy, revealing a small transferred magnetic hyperfine field below 7 K.

Contribution

It provides detailed Moessbauer spectroscopic analysis of LaFePO, highlighting magnetic interactions at low temperatures and clarifying the material's superconducting and magnetic characteristics.

Findings

Superconductivity observed at 7 K in LaFePO.

Weak transferred magnetic hyperfine field detected at 4 K.

Single Fe signals with isomer shifts around 0.35 mm/s.

Abstract

A polycrystalline sample of superconducting LaFePO was prepared in a tin flux at 1123 K. The structure was determined from single crystal data (ZrCuSiAs-type, P4/nmm, a = 3.9610(1), c = 8.5158(2) A, Z = 2) and the phase analysis was performed by the Rietveld method. LaFePO is Pauli-paramagnetic and becomes superconducting at 7 K after removing the ferromagnetic impurity phase Fe2P from the sample. 57Fe Moessbauer spectroscopy measurements at 298, 77, 4.2 and 4 K show single signals at isomer shifts around 0.35 mm/s, subject to weak quadrupole splitting. At 4 K, a symmetric line broadening appears, resulting from a small transferred magnetic hyperfine field of 1.15(1) T and accompanied by an angle of 54.7(5) between Bhf and Vzz, the main component of the electric field gradient tensor.