Strain-Mediated Giant Magnetoelectric Coupling in a Crystalline Multiferroic Heterostructure.

Adrián Begué,Miguel Ciria

doi:10.1021/acsami.0c18777

Abstract

Multiferroic heterostructures based on the strain-mediated mechanism present ultralow heat dissipation and large magnetoelectric coupling coefficient, two conditions that require endless improvement for the design of fast nonvolatile random access memories with reduced power consumption. This work shows that a structure consisting of a [Pb(Mg1/3Nb2/3)O3]0.7-[PbTiO3]0.3 (001) substrate on which a crystalline FeGa(001)/MgO(001) bilayer is deposited exhibits a giant magnetoelectric coupling coefficient of order 15 × 10–6 s m–1 at room temperature. That result is a 2-fold increment over the previous highest value. The spatial orientation of the magnetization vector in the epitaxial FeGa film is switched 90° with the application of electric field. The symmetry of the magnetic anisotropy is studied by the angular dependence of the remanent magnetization, demonstrating that poling the sample generates a switchable uniaxial magnetoelastic anisotropy in the film that overcomes the native low 4-fold magnetocrystalline anisotropy energy. Magnetic force microscopy shows that the switch of the easy axis activates the displacement of domain walls and the domain structures remain stable after that point. This result highlights the interest in single-crystalline structures including materials with large magnetoelastic coupling and small magnetocrystalline anisotropy for low-energy-consuming spintronic applications.

Highlights

This request has motivated the evolution of the vintage idea of a material with interconnected magnetic and electric capacities3 into sophisticates magnetoelectric (ME) heterostructures encompassing components with enhanced ferroelectric (FE) and ferromagnetic (FM) properties.4−7 For the latter structures, the ME coupling strength can be three or more orders of magnitude8−10 higher than that for single-phase materials11,12 and the active control of the magnetic state by the FE part of the structure can be achieved at room temperature
The multiferroic heterostructure consists of a PMN−PT(001) FE substrate, coated with a crystalline MgO(001) seed layer (≈ 3 nm in thickness) for a FeGa(001) magnetic layer approximately 15 nm thick and a Mo overcoat 2 nm thick
Multiferroic structure with 10−6 s m−1 is obtained giant in a value for αE of full crystalline heterostructure at room temperature

Summary

INTRODUCTION

The processing of information requires very efficient devices with low-energy consumption, a goal that is hampered if electric current is used to switch nonvolatile states. This request has motivated the evolution of the vintage idea of a material with interconnected magnetic and electric capacities into sophisticates magnetoelectric (ME) heterostructures encompassing components with enhanced ferroelectric (FE) and ferromagnetic (FM) properties.− For the latter structures, the ME coupling strength can be three or more orders of magnitude− higher than that for single-phase materials and the active control of the magnetic state by the FE part of the structure can be achieved at room temperature. Several mechanisms are capable of controlling the magnetization M without magnetic field or electric current.− One of them is based on the strain transferred from the FE crystal to a FM film, which generates a uniaxial magnetic anisotropy through the magnetoelastic coupling effect.− Other mechanisms are based on phenomena located at the FE-FM interface: modification of the population of spin-up and spin-down electron density of states and voltage-driven oxygen migration and modification of the oxide ferromagnet. The strain-transfer mechanism shows lower heat dissipation per switching cycle and presents larger magnetoelectric coupling parameter αE than any other coupling mechanism.. The processing of information requires very efficient devices with low-energy consumption, a goal that is hampered if electric current is used to switch nonvolatile states.1,2 This request has motivated the evolution of the vintage idea of a material with interconnected magnetic and electric capacities into sophisticates magnetoelectric (ME) heterostructures encompassing components with enhanced ferroelectric (FE) and ferromagnetic (FM) properties.− For the latter structures, the ME coupling strength can be three or more orders of magnitude− higher than that for single-phase materials and the active control of the magnetic state by the FE part of the structure can be achieved at room temperature.. FeGa crystalline films with intrinsic small cubic magnetic anisotropy and large magnetostriction can improve the performances of magnetoelectronic devices based on converse magnetoelectric mechanisms

RESULTS AND DISCUSSION

CONCLUSIONS

■ ACKNOWLEDGMENTS

■ REFERENCES