Neutron powder diffraction investigation of the structural and magnetic properties of (La1-yYy)FeAsO

TL;DR

This study explores how yttrium substitution in (La1-yYy)FeAsO affects its structural, magnetic, and resistive properties, revealing a correlation between chemical pressure and transition temperatures using neutron diffraction and resistivity measurements.

Contribution

It provides new insights into the relationship between chemical substitution and phase transitions in (La1-yYy)FeAsO, highlighting a possible Jahn-Teller distortion mechanism.

Findings

Structural and magnetic transition temperatures decrease with Y substitution.

Structural transition may be caused by Jahn-Teller distortion involving Fe orbitals.

Magnetic order develops after structural transition.

Abstract

The structural, magnetic and resistive properties of (La1-yYy)FeAsO compounds (y = 0.10, 0.20, 0.30) have been investigated by means of X-ray and neutron powder diffraction as well as by resistivity measurements. The temperatures at which the structural transition from tetragonal to orthorhombic and the magnetic ordering take place progressively reduce by similar amounts with increasing Y substitution on account of the progressive chemical pressure increase. We propose that the structural transition could be originated by a cooperative Jahn-Teller distortion involving the alignment of the fully occupied Fe 3d(z2) orbitals in the Fe plane along the y axis, leading to the branching of the cell parameters a and b. The magnetic structure develops after the occurrence of the structural transition, but before its completion.