Biaxial Strain in the Hexagonal Plane of MnAs Thin Films: The Key to Stabilize Ferromagnetism to Higher Temperature

TL;DR

This study shows that biaxial strain in MnAs thin films stabilizes ferromagnetism at higher temperatures by influencing phase coexistence, with elastic neutron scattering revealing temperature-dependent strain effects.

Contribution

It demonstrates that biaxial strain in the hexagonal plane is crucial for extending ferromagnetic stability in MnAs thin films beyond room temperature.

Findings

Biaxial strain causes alpha-beta phase coexistence in MnAs.

Ferromagnetic alpha-phase persists up to 350 K due to strain effects.

Temperature-dependent strain explains phase transition behavior.

Abstract

The alpha-beta magneto-structural phase transition in MnAs/GaAs(111) epilayers is investigated by elastic neutron scattering. The in-plane parameter of MnAs remains almost constant with temperature from 100 K to 420 K, following the thermal evolution of the GaAs substrate. This induces a temperature dependent biaxial strain that is responsible for an alpha-beta phase coexistence and, more important, for the stabilization of the ferromagnetic alpha-phase at higher temperature than in bulk. We explain the premature appearance of the beta-phase at 275 K and the persistence of the ferromagnetic alpha-phase up to 350 K with thermodynamical arguments based on the MnAs phase diagram. It results that the biaxial strain in the hexagonal plane is the key parameter to extend the ferromagnetic phase well over room temperature.