Evolution of the magnetic phase transition in MnO confined to channel type matrices. Neutron diffraction study

TL;DR

This study investigates how confining MnO in nanochannels alters its magnetic phase transition from first order to continuous, with transition temperature and critical behavior depending on channel size, explained via Landau theory.

Contribution

It reveals the evolution of magnetic phase transition nature in MnO confined to nanochannels, showing size-dependent transition characteristics and providing a theoretical explanation.

Findings

Transition becomes continuous in confined MnO

Transition temperature exceeds bulk Néel temperature

Critical exponent decreases with smaller channels

Abstract

Neutron diffraction studies of antiferromagnetic MnO confined to MCM-41 type matrices with channel diameters 24-87 A demonstrate a continuous magnetic phase transition in contrast to a discontinuous first order transition in the bulk. The character of the magnetic transition transforms with decreasing channel diameter, showing the decreasing critical exponent and transition temperature, however the latter turns out to be above the N\'eel temperature for the bulk. This enhancement is explained within the framework of Landau theory taking into consideration the ternary interaction of the magnetic and associated structural order parameters.