Multiferroics: back to the spotlight
Vassil Skumryev
Institució Catalana de Recerca i Estudis Avançats (ICREA), and
Departament de Física, Universitat Autònoma de Barcelona, Spain
In the first part of the talk I will briefly review the history of magnetoelectric effect, which was foreseen by Pierre Curie in 1894, and the related to this effect multiferroics (magnetoelectric materials in which long range magnetic and polar orders coexist and are mutually dependent). After being almost abandoned for a long period of time, in our days there is a revival of the interest to multiferroic materials, primary fueled by the opportunity, which they could eventually provide, to control the magnetic order via electric field and vice versa. Such control would allow overcoming critical limitations in spintronics technology.
In the second part of the talk I will discuss the recent advances in the attempts for electrical field control over the magnetic exchange bias in multiferroics based heterostructures. Magnetic exchange bias (EB) is an effect at the interface between ferromagnetic (FM) and antiferromagnetic (AFM) materials, and is indispensible in spin valves and magnetic random access memory. The most-known EB manifestation is the magnetic hysteresis loop shift along the magnetic field axis, when the system is cooled trough the Neel temperature in magnetic field. This shift can be either in ?negative" or in ?positive" field direction. We have found that the electric field can be used to tune the exchange bias in AF/FM heterostructures and eventually the magnetic switching of the FM layer. Consequently, the sign of the EB can be reversibly switched. We have demonstrated this effect using soft ferromagnetic thin film of Permalloy deposited on the basal plane of hexagonal RMnO3 antiferromagnetic multiferroic (thin film or single crystal). The scenario which we propose to explain this unconventional EB effect is based on the possibility to alter the clamped magnetic and ferroelectric domains of the multiferroic by electric field and thus to modify the pinning torque exerted on the FM moments by the AFM multiferroic. This finding may contribute to paving the way towards a new generation of electric field controlled spintronic devices.