Superconductivity in NdFe1-xCoxAsO (0.05 < x < 0.20) and rare-earth magnetic ordering in NdCoAsO

TL;DR

This study explores the phase diagram, superconducting properties, and magnetic ordering in NdFe1-xCoxAsO, revealing a superconducting dome, magnetic transitions, and structural distortions, with implications for understanding cobalt-doped iron-based superconductors.

Contribution

It provides detailed insights into the structural, magnetic, and superconducting properties of NdFe1-xCoxAsO across various doping levels, including the phase diagram and magnetic ordering.

Findings

Superconducting dome with maximum Tc of 16.5 K at x=0.12.

NdCoAsO is an itinerant ferromagnet with TC=85 K.

Underdoped samples show orthorhombic distortions at low temperatures.

Abstract

The phase diagram of NdFe1-xCoxAsO for low cobalt substitution consists of a superconducting dome (0.05 < x < 0.20) with a maximum critical temperature of 16.5(2) K for x = 0.12. The x = 1 end member, NdCoAsO, is an itinerant ferromagnet (TC = 85 K) with an ordered moment of 0.30(1) BM at 15 K. Below TN = 9 K, Nd spin-ordering results in the antiferromagnetic coupling of the existing ferromagnetic planes. Rietveld analysis reveals that the electronically important two-fold tetrahedral angle increases from 111.4 to 115.9 deg. in this series. Underdoped samples with x = 0.046(2) and x = 0.065(2) show distortions to the orthorhombic Cmma structure at 72(2) and 64(2) K, respectively. The temperature dependences of the critical fields Hc2(T) near Tc are linear with almost identical slopes of 2.3(1) T K-1 for x = 0.065(2), x = 0.118(2) and x = 0.172(2). The estimated critical field Hc2(0) and correlation length for optimally doped samples are 26(1) T and 36(1) Angstrom. A comparison of the maximum reported critical temperatures of well-characterized cobalt doped 122- and 1111-type superconductors is presented.