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Multifunctional ceramic layers with high electromagnetoelastic coupling in complex geometries

Final Report Summary - MULTICERAL (Multifunctional ceramic layers with high electromagnetoelastic coupling in complex geometries)

This MULTICERAL project was initially focused on the strengthening of cross-coupling effects (between magnetic, electric, and elastic properties) via development of novel single-layer films and composites of thereof in complex geometries and, based on that, on the development of prototypes and testing them for use in the industrial applications.

The project was structured into six Work packages (WP), as follows:

WP 1. Films in planar geometries
Objectives: to develop single layers of ferromagnetics, multiferroics and relaxors on standard and 'active' substrates, as well as bi- and multilayers of these compounds.

WP 2. Hybrid composites
- to develop technology for the deposition of 0-3 piezoelectric- magnetic composites;
- to optimise the properties of composites by varying processing parameters and connectivity of its constituents.

WP 3. Ferroic tubes and nanowires
Objectives: to develop and to study multifunctional films in cylindrical geometries (tubes, wires) of ferroelectric Pb(Zr (Zr,Ti)O3 (PZT) and multiferroic BiFeO3 (BFO) using porous Si templates.

WP 4. Advanced characterisation and modelling
- full characterisation of the fabricated structures by using macroscopic (magnetic, dielectric and ferroelectric) and microscopic (TEM, XRD, EDX, Raman) techniques and NMR;
- modelling of cross-coupling effects in different geometries;
- finite element analysis of some of the fabricated structures.

WP 5. Design, fabrication and testing of prototypes
Objectives: to design, to fabricate and to test at least two simple structures related to multifunctional films as described in WP1-3:
(i) monolithic films deposited on wafers; and / or (ii) magnetic / piezoelectric cantilever; and / or (iii) magnetically tuned capacitor.

WP 6. Coordination and management
Objectives: smooth running of the project, achievement of all objectives planned, internal evaluation of project progress, protection of all intellectual property, resolution of the conflicts.

WP 7. Training, dissemination and exploitation of the results
- to guarantee internal and external dissemination of results;
- to guarantee a necessary protection of intellectual property within the project;
- to organise workshop opened to a broad industrial and research community;
- to evaluate potential markets for the produced prototypes;
- to prepare the report for the exploitation of the results.

In general, the objectives that were planned for the total duration of the project were successfully (at least partly) achieved.

In WP1, several series of films in planar geometries have been deposited and evaluated: BFO (including doped films that showed the best performance in the ceramic form), PFN, CRO, NMG using both single target sputtering and co-sputtering from three targets, e-beam evaporation, and PLD. Bilayers and multilayers including BFO / BaTiO3 and NMG / PZT were successfully deposited and characterised. They showed high enough structural and surface quality in order to start testing their electrical, magnetic and cross-coupling properties. The measurements of magnetic properties confirmed that doped films possess higher magnetisation (especially, BFO / BaTiO3 multilayers where the doping effect could be amplified by the interface stress). The release of hidden magnetisation (1-2 emu/g) has been observed in BiFeO3 ceramics doped with diamagnetic A-site substitutions. Giant piezoelectric effect (d33 = 9000 pm/V) was observed in PMN-PT 'active' substrates that was used to obtain giant magnetoelectric effect in films deposited on it. The patent application is prepared that describes proprietary method of poling relaxor single crystals. Novel structures of PFN / PMN-PT bi- and multilayers were prepared and characterised. The fabrication of CRO films finally allowed increasing blocking temperatures and fabrication of exchange bias memory prototype. Bilayer films, e.g. BiFeO3 / BaTiO3 or BiFeO3 / PbTiO3 were characterised in terms of their magnetic properties and coupling. Novel multiferroic PFN (PbFe1 / 2Nb1 / 2O3) and its solid solutions with PMW (PbMg1 / 2W1 / 2O3) were fabricated as films and tested for coupling properties. Relaxor superlattices [Pb(MgNb)O3 / [PbTiO3] and BaTiO3 / Ba(Ti,Zr)O3 were tested as well as several ferromagnetic / ferroelectric compositions (NiFe2O4/PZT and PFN/PZT). High-quality NiMnGa single layer films (NiMnGa / Si, NiMnGa / PMN-PT) and composite bi-layers (NiMnGa / PZT) were successfully fabricated and tested.

In WP2, relaxor / piezoelectric sol-gel composites were successfully deposited and evaluated. They demonstrated sufficiently high temperature-independent dielectric constant in the broad range of temperatures and frequencies. Novel ferroelectric / ferromagnetic PZT / NFO sol-gel films were prepared and analysed in terms of their structural and magnetic properties.

Their electrical characterisation was not complete because of the problems with electrical conductivity and inability to apply high electric field to verify magnetoelectric coupling. The stress sensor based on relaxor / PZT composite film was demonstrated.

In WP3, high-quality ferroelectric PZT nanotubes were produced (including those on carbon nanotubes) and their properties were evaluated by piezoresponse force microscopy and EPR. It has been shown that they are indeed ferroelectric with sufficiently high piezoelectric properties and electric field-induced deformations potentially useful for various applications (e.g. microfluidic devices). The PZT nanotubes with electrodes were produced and (even being conducting) could be tested with analytical methods. The prototype showing high intensity of THz emission from PZT nanotubes was demonstrated.

In WP4, detailed investigation of structural, electrical and magnetic properties of deposited films was undertaken. Local structure of BFO and NMG was determined by the magnetic resonance techniques and direct magnetisation measurements. Quadratic magnetoelectric coupling in PFN was discovered and explained. Giant magnetoelectric effect was predicted in ferroic nanorods due to intrinsic stress. The effect of the giant magnetoelectric effect induced by surface stress was further theoretically elaborated, for example, in case of magnetic substrate with deposited epitaxial ferroelectric film. It was shown that magnetoelectric effect can be as high as 50 V/cm-1Oe-1 if the proper combination of materials is used. Also, it was shown that the misfit strain may increase quadratic ME coupling and modify the phase diagram. First encouraging results were obtained on multiferroic fluorides. A very sensitive setup for the measurements of magnetoelectric effect based on commercial SQUID was developed and tested. A novel method for the FEM calculation of the multiferroic structures using standard codes was proposed and realised by ONERA.

Finally, in WP5, the specific test prototypes to be used for structure health monitoring were designed, manufactured, and tested by the MULTICERAL partners. Several additional prototypes have been demonstrated including stress sensor and exchange bias magnetic device. Several MULTICERAL workshops have been conducted (e.g. one within symposium 'Piezoresponse force microscopy and nanoscale phenomena in polar materials' in Portugal). Several partners of MULTICERAL gave plenary and invited lectures at various international congresses and meetings thus contributing to dissemination pf the project. National patent was received describing the procedure of fabrication of composite hybrid films.