Exchange-biased SiO2/Co/CoO granular multilayers deposited by sequential sputtering

M Gamino,S Michea,J.C Denardin,L.F Schelp,M.A Correa,F Bohn,L.S Dorneles

doi:10.1016/j.jmmm.2017.04.095

Abstract

We investigate the magnetic properties in a system engineered to present Co grains laterally surrounded by a CoO matrix. By considering ferromagnetic SiO2/Co/CoO granular multilayers produced by sequential sputtering deposition, we verify that the Co grains present strong interfacial exchange coupling with the CoO matrix, assigned by the exchange bias effect as well as the raise of the Co blocking temperature. Morever, through magnetization and Hall resistivity experiments, we observe that the antiferromagnetic ordering temperature and exchange bias are dependent on the thickness of the antiferromagnetic material, attributed to finite size effects, as well as we find that the Co blocking temperature is raised as the CoO layer becomes thicker. We discuss the experimental results in terms of the growth mode of the layers, morphological properties of the multilayers, and temperature dependence of the magnetic behavior. The results place the sequential sputtering deposition as a promising alternative technique to produce Co/CoO granular multilayers.

Highlights

The exchange bias (EB) effect is primarily characterized by the displacement of the magnetic hysteresis loop along the magnetic field axis [1,2]
We investigate the magnetic properties and exchange bias effect in a system engineered to present Co grains laterally surrounded by the CoO matrix
We consider ferromagnetic SiO2/Co/CoO granular multilayers produced by sequential sputtering deposition, and verify the morphological properties, through transmission electron microscopy, as well as the magnetic behavior, via temperature dependence of the magnetization, Hall resistivity, and magnetization curves

Summary

Introduction

The exchange bias (EB) effect is primarily characterized by the displacement of the magnetic hysteresis loop along the magnetic field axis [1,2]. In Co/CoO core–shell structures, the strains at the interface along specific crystallographic directions affect the core/shell magnetic coupling, and bring the CoO Néel temperature down to $ 235 K, well below the value verified for bulk systems, $ 293 K [28] In this case, finite size effects associated to the CoO shell dimension seem to be less pronounced than those found in multilayers where CoO films are intercalated with non-magnetic films [29,24]. The results place the sequential sputtering deposition as a promising alternative technique to produce Co/ CoO granular multilayers

Experiment

Results and discussion

Conclusion