Enhancement of ferromagnetism upon thermal annealing in pure ZnO

TL;DR

This study demonstrates that thermal annealing significantly enhances ferromagnetism in pure ZnO, achieving a transition temperature above room temperature, likely due to vacancy cluster interactions.

Contribution

It reveals a novel method to induce and enhance ferromagnetism in pure ZnO through thermal annealing, highlighting the role of vacancy clusters in magnetic behavior.

Findings

Ferromagnetic transition temperature above room temperature

Finite coercive field up to 300K

Thermoremanent magnetization up to 340K

Abstract

We report here enhancement of ferromagnetism in pure ZnO upon thermal annealing with the ferromagnetic transition temperature Tc above room temperature. We observe a finite coercive field upto 300K and a finite thermoremanent magnetization upto 340K for the annealed sample. We propose that magnetic moments can form at anionic vacancy clusters. Ferromagnetism can occur due to either superexchange between vacancy clusters via isolated F+ centers, or through a limited electron delocalization between vacancy clusters. Isolated vacancy clusters or isolated F+ centers give rise to a strong paramagnetic like behaviour below 10K.