Neutron Diffraction Study of anomalous negative thermal expansion in non-superconducting PrFe1-xRuxAsO

TL;DR

This study uses neutron diffraction to explore the structural and magnetic properties of PrFe1-xRuxAsO, revealing persistent negative thermal expansion and its potential link to the absence of superconductivity.

Contribution

It demonstrates that Ru doping suppresses phase transitions without inducing superconductivity and identifies negative thermal expansion as a common feature in these materials.

Findings

Negative thermal expansion occurs along the c-axis from 60K to 4K.

Suppression of phase transitions does not lead to superconductivity.

NTE is present across all Ru doping levels studied.

Abstract

Neutron powder diffraction has been used to investigate the structural and magnetic behavior of the isoelectronically doped Fe pnictide material PrFe1-xRuxAsO. Substitution of Ru for Fe suppresses the structural and magnetic phase transitions that occur in the undoped compound PrFeAsO. Contrary to the behavior usually observed in 1111 pnictide materials, the suppression of both the structural and magnetic transitions does not result in the emergence of superconductivity or any other new ground state. Interestingly, PrFeAsO itself shows an unusual negative thermal expansion (NTE) along the c-axis, from 60K down to at least 4K; this does not occur in superconducting samples such as those formed by doping with fluorine on the oxygen site. We find that NTE is present for all concentrations of PrFe1-xRuxAsO with x ranging from 0.05 to 0.75. These results suggest that the absence of superconductivity in these materials could be related to the presence of NTE.