VOLtAge COntrolof NANOmagnet – VOLCONANO

Controlling nanomagnetism by means of an electric field is a key issue for the future development of low-power spintronic. In this context, near equiatomic composition, the CsCl-like B2 chemically ordered FeRh alloy which presents a métamagnetic transition from a low temperature antiferromagnetic order to a high temperature ferromagnetic order just above room temperature, is a very good candidate for assessing magnetic control through external stimuli. Recently, a ferroelectric crystal has been used to electrically drive the temperature of such metamagnetic phase transition (MPT) of epitaxially grown FeRh films with only a few volts, with potential media applications for thermally assisted magnetic recording. This effect may be the signature of magnetic exchange correlations, acting at shorter-range in the AF phase than in the FM one. In order to achieve a better understanding and control of such metamagnetic phase transition, we propose to explore the finite size effect in multiferroic heterostructure at the ultimate nanoscale. Thus, monodomain FeRh nanomagnets will be grown on ferroelectric crystals of different nature, such as BaTiO3 and LiNbO3, of different crystalline orientation, enabling a tuning of ferroelectric polarization, surface chemistry and strain, in view to decouple the effects of these different parameters on magneto-electric responses. Our aim is to precisely describe the nature of the metamagnetic phase transition in FeRh and to harness the benefits to manipulate magnetic order in nanoparticles by applying an electric field. In a first step, we will try to induce the progressive change in magnetic order in B2-FeRh nanoparticles in the 2-8 nm diameter range deposited on a piezo and ferroelectric BaTiO3 substrate under electric field. We will then combine FeRh NPs with ferroelectric crystals, as LiNbO3, which can be acquired with pre-polarized up and down ferroelectric domains, to disentangle the surface potential effect. Beyond working with ferroelectric single crystals, we will propose integrated devices combining the NPs with ferroelectric and piezoelectric Pb(Zr,Ti)O3 thin films, which have already been used in artificial multiferroic spintronic devices. Finally to discard magneto-strictive effects, we would use other dielectric layer like ZrO2 or HfO2, having a large dielectric constant and a large breakdown field, allowing for large screening charges accumulation. Indeed the high sensitivity of the nanomagnets to their surface atoms offers the great opportunity to increase interface magnetoelectric coupling and to modify the electronic structure in hybrid multiferroic nanostructures. Operando studies on the electronic properties of these systems under external voltage stimuli will be carried out to modify on demand the charge and strain states on FeRh nanoclusters and thus the metamagnetic phase transition. In the frame of CES 09 – “Nanomatériaux et nanotechnologies pour les produits du future”, the hybrid metamagnetic nanostructure/ferroelectric material system proposed in the present project is based on an interface control which confers multifunctional properties to the system. The goal of this proposal is to develop an artificial hybrid multiferroic device based on magnetic FeRh nanoclusters grown on ferroelectric (FE) substrate to study both ferroic orders by electrical polarization. Indeed, such a system presents a particular interest for future devices due to the non-volatility of the information which can be stored in nanomagnets with proper anisotropy and the low power consumption associated with voltage control. From a fundamental point of view, in order to better understand the magnetoelectric coupling occurring at interface, we propose to explore the AF/FM transition from the study of original hybrid multiferroic device based on FeRh nanomagnet grown on ferroelectric crystal which could be useful in future applications related to quantronics.