Crafting the strain state in epitaxial thin films: A case study of CoFe2O4 films on Pb(Mg,Nb)O3-PbTiO3

TL;DR

This paper investigates how strain influences the electric and magnetic properties of epitaxial CoFe2O4 thin films on piezoelectric substrates, exploring phase transitions and magnetoelectric coupling through experimental techniques.

Contribution

It provides a systematic study of strain effects and phase transitions in Pb(Mg,Nb)O3-PbTiO3 crystals and examines the strain state and magnetoelectric coupling in CoFe2O4 films.

Findings

Strain states vary with temperature and electric field.

Giant magnetoelectric coupling observed in CoFe2O4 films.

Different phase transition pathways identified.

Abstract

The strain dependence of electric and magnetic properties has been widely investigated, both from a fundamental science perspective and an applications point of view. Electromechanical coupling through field-induced polarization rotation (PRO) and polarization reorientation (PRE) in piezoelectric single crystals can provide an effective strain in film/substrate epitaxial heterostructures. However, the specific pathway of PRO and PRE is a complex thermodynamic process, depending on chemical composition, temperature, electric field and mechanical load. Here, systematic studies of the temperature-dependent field-induced phase transitions in Pb(Mg,Nb)O3-PbTiO3 single crystals with different initial phase and orientation configurations have been performed. Different types of strains, volatile/nonvolatile and biaxial/uniaxial, have been measured by both macroscopic and in-situ X-ray diffraction techniques. In addition, the strain state of epitaxial Mn-doped CoFe2O4 thin films was examined by magnetic anisotropy measurements, where a giant magnetoelectric coupling has been demonstrated.