Superconductivity in LnFePO (Ln = La, Pr, and Nd) single crystals

TL;DR

This study reports the synthesis and characterization of LnFePO (Ln = La, Pr, Nd) single crystals, revealing superconductivity in PrFePO and NdFePO with low T_c values, and compares these to related LnFeAsO compounds to explore differences in their superconducting mechanisms.

Contribution

It provides new insights into the superconducting properties of LnFePO compounds and compares them systematically with LnFeAsO_{1-x}F_x, highlighting potential differences in their origins.

Findings

PrFePO and NdFePO are superconducting with T_c around 3 K.

Annealing affects the properties of the compounds.

LnFePO compounds are structurally similar to LnFeAsO_{1-x}F_x but differ in superconductivity origin.

Abstract

Single crystals of the compounds LaFePO, PrFePO, and NdFePO have been prepared by means of a flux growth technique and studied by electrical resistivity, magnetic susceptibility and specific heat measurements. We have found that PrFePO and NdFePO display superconductivity with values of the superconducting critical temperature T_c of 3.2 K and 3.1 K, respectively. The effect of annealing on the properties of LaFePO, PrFePO, and NdFePO is also reported. The LnFePO (Ln = lanthanide) compounds are isostructural with the LnFeAsO_{1-x}F_x compounds that become superconducting with T_c values as high as 55 K for Ln = Sm. A systematic comparison of the occurrence of superconductivity in the series LnFePO and LnFeAsO_{1-x}F_x points to a possible difference in the origin of the superconductivity in these two series of compounds.