New synthesis route and magnetic structure of Tm2Mn2O7 - pyrochlore

TL;DR

This paper introduces a new chemical synthesis method for Tm2Mn2O7 pyrochlore, revealing its magnetic structure and phase transition at low temperatures using neutron diffraction and symmetry analysis.

Contribution

A novel synthesis route for Tm2Mn2O7 pyrochlore at ambient pressure and detailed magnetic structure analysis using neutron diffraction and symmetry considerations.

Findings

Pure Tm2Mn2O7 phase obtained at 1100°C and 1300 bar oxygen pressure

Observation of a magnetic transition below 25K with ferromagnetic and antiferromagnetic features

Detection of magnetostriction effect associated with the magnetic transition

Abstract

In this work we present a new chemical route to synthesize Tm2Mn2O7 pyrochlore, a compound which is thermodynamically unstable at ambient pressure. Differently from the reported in the past high pressure synthesis of the same compound applying oxides as starting materials, we have obtained a pure phase Tm2Mn2O7 by a converting TmMnO3 at 1100 C and 1300 bar oxygen pressure. The studies of Tm2Mn2O7 performed by a high resolution neutron powder diffraction have shown, that a pure pyrochlore cubic phase Tm2Mn2O7 (space group Fd-3m) have been obtained. On cooling below 25K there is a transition to a ferromagnetically (FM) ordered phase observed with an additional antiferromagnetic (AFM) canting suggesting a lowering of the initial cubic crystal symmetry. The magnetic transition is accompanied by small but well visible magnetostrsiction effect. Using symmetry analysis we have found a solution for the AFM structure in the maximal Shubnikov subgroup I41/am'd'.