Polarisable Materials and Magnetoelectric Nanostructures

Research activity in the “Polarisable Materials and Functional Nanostructures” group of IFIMUP-IN was focused on a diversified study of materials with interesting magnetic, dielectric properties that made them excellent candidates for the processing and development of devices for emerging technologies. Studying those materials has given rise to further new, challenging fundamental questions, whose answers have turned out to be important in gaining better knowledge of the actual physical mechanisms, and in improving their properties with regard to their technological applications. The following topics have been addressed: competitive interactions, Proton-glass state, relaxation processes, relaxors, non-linear rotation quantum dynamics, magnetoelectric effect and multiferroicity, spin-phonon (pseudospin) coupling, ordering in crystalline soft matter, the role of spin fluctuations and hybridisation effects on the electrical properties of R-T metallics.

Our Team

OBJECTIVES

Research activity has been focused on the following topics: competitive magnetic/electric interactions, relaxation processes, statics and dynamics in polarizable thin films and heterostructures, magnetoelectric effect, spin-phonon coupling, multifunctionality at nano-scale, specially in electrically driven spintronics.

In this scope, several systems have been selected which involve mainly transition metal oxides (TMOs). In these systems as it was reckoned in the past by Landau, the concept of symmetry breaking is a fundamental issue for understanding some of the more distinctive physical properties of TMOs: ferroelectricity, ferromagnetism, and superconductivity can be readily explained by spacial inversion, time reversal and Gauge symmetry breaking, respectively. These phenomena emerge from the collective behaviour of electrons, by the interplay among electronic degrees of freedom. In this regard, both electrically and magnetically polarisable materials, or of both kinds have been investigated. Special attention has been paid to those, which exhibit spin-phonon coupling and/or magnetoelectric effect. Moreover, micro- and nanostructured composites were produced based on oxides in order to profit from their different properties, which could be enhanced through the balance of crossed electric/strain coupling mechanisms.

Another main objective of the group in addressed to medical applications: cancer detection using non-evasive like Raman and THz spectroscopies, in order to exclude chirurgical intervention to obtain information about the sort of lesion.

A new objective has been to establish the basis for a consistent group of collaborators, in both the scientific and educational research fields of interactive materials and experiments, as tools for a better understanding and spreading of fundamental knowledge in Science and their applications. Publishing of works in this field is also aimed.

Experimental studies have been performed on samples having diverse forms and shapes, ranging from monocrystals, bulk ceramics, ultra-thin films and multilayers, to nanostructures. In order to study some of their properties medium high magnetic dc fields (up to 7 T), and extremely high pressures (60 Gpa) have been used, whenever applicable. Moreover, dimension-size effects were also envisaged, in the materials under investigation. A set of available techniques in place or from collaboration with other research groups has been used.

MAIN ACHIEVEMENTS

1. The (x, T) phase diagram of Eu(1-x)Lu(x)MnO(3), 0<=x<=0.2, reflects the effect of lattice distortions induced by the isovalent substitution of Eu(3+) by Lu(3+) ions, which gradually unbalances the antiferromagnetic against the ferromagnetic interactions, enabling both ferroelectricity and magnetoelectric coupling.

2. Three different regions can be distinguished in the temperature dependence of ac conductivity of YMnO(3) ceramics annealed under different atmospheres. Oxygen vacancies are responsible for the dielectric anomaly observed at < 400 degrees C. For temperatures > 400 degrees C, dielectric data are influenced by conductivity. No ferroelectricity is observed.

3. Dielectric relaxations of K(1-x) Li(x) TaO(3) ceramics observed are ascribed to individual hopping by 90 degrees, 180 degrees of dipoles created by off-centre Li ions, to 180 degrees-flips of Li pairs for x = 0.02 and of polar clusters of interacting Li ions for x = 0.05 and 0.10. Additional relaxation is presented for x = 0.10 and attributed to 90 degrees-reorientation of Li polar clusters. P(E) curves around the relaxation temperatures show that dynamics in this system can be understood as a crossover from a dipolar glass to a relaxor-like behaviour.

4. A novel/general chemical solution route for processing high- manganite thin films is revealed for LaMnO(3), EuMnO(3) and DyMnO(3) thin films. X-ray diffraction and Raman spectroscopy, SEM and AFM techniques show a progressive improvement of the films with increase of annealing temperature. Magnetic response of those films shows transition temperatures compared with those reported for crystals and ceramics.

5. Polarization curves through magnetic phases of the orthorhombic Eu(1-x)Y(x)MnO(3) reveal the existence of a re-entrant improper ferroelectric phase for x = 0.2, 0.3 and 0.5. A ferroelectric phase is also stable for x = 0.4 not vanishing down to 7 K. The corresponding (x, T) phase diagram was traced.

6. The effect of Sr vacancies on the behavior of SrTiO3 doped with (La(3+), Gd(3+), and Y(3+)) substituting Sr(2+) ions is unravelled: (i) A remarkable shift of antiferrodistortive transition temperature T(a) for just a small dopant content. (ii) Unique linear dependence of Ta versus tolerance factor is obtained when Sr-vacancies are considered; (iii) A vacancy size of 1.54 angstrom is estimated (7% larger than Sr(2+) radius).

7. Feasibility of Raman spectroscopy for discriminating between adenocarcinomatous and normal mucosal formalin-fixed colonic tissues was evidenced. Unlike earlier studies in colorectal cancer, a spectral deconvolution model was implemented to derive spectral information. The bands with higher diagnosis relevance detected by spectra deconvolution enable to confine the study to the spectral regions 800-1800 cm^-1. Tissue discrimination were associated with nucleic acids (1344 cm^-1) and aromatic aminoacids (1587 cm^-1). A critical view along with a comparison of our results to earlier ones is presented.

8. Human normal and cancer-affected colon tissues have been studied using transmission time-domain THz spectroscopy and continuous wave THz imaging. We show that it is possible to distinguish between normal and cancerous regions in the samples when they are fixed in formalin or embedded in paraffin. Additional contrast-contributing factors other than water should be considered.

9. Development of new experiments and instructional materials to present the research activities in IFIMUP to new students. Efforts to disseminate science and the research carried out in IFIMUP in talks and seminars, activities in schools, visits to IFIMUP laboratories, as well as participating in “open days” and science fairs.

PUBLICATIONS 2012-2013

Structural and electrical properties of LuMnO3 thin film prepared by chemical solution method. Y. Romaguera Barcelay, J. Agostinho Moreira, A. Almeida, J. Peréz de la Cruz. Thin Solid Films, Volume 520, Issue 6, 1 January (2012).

Dimensional effects on the structure and magnetic properties of GdMnO3 thin films. Y. Romaguera-Barcelay, J. Agostinho Moreira, A. Almeida, J.P. Araújo, J. Pérez de la Cruz. Materials Letters 70, 167–170 (2012).

Low-temperature dielectric response of NaTaO3 ceramics and films. A. Tkach, A. Almeida, J. Agostinho Moreira, J. Perez de la Cruz, Y. Romaguera-Barcelay, and P. M. Vilarinho. Appl. Phys. Lett. 100, 192909 (2012).

Magnetically-induced lattice distortions and ferroelectricity in magnetoelectric GdMnO3, Agostinho Moreira, J., Almeida, A., Chaves, M. R., Kreisel, J., Oliveira, J., Carpinteiro, F., Tavares, P. B., JOURNAL OF PHYSICS-CONDENSED MATTER Volume: 24 Issue: 43 Article Number: 436002 (2012)

Effect of Pt bottom electrode texture selection on the tetragonality and physical properties of Ba0.8Sr0.2TiO3 thin films produced by pulsed laser deposition, Silva, J. P. B., Sekhar, K. C., Almeida, A., Moreira, J. Agostinho, Martin-Sanchez, J., Pereira, M., Khodorov, A., Gomes, M. J. M., JOURNAL OF APPLIED PHYSICS Volume: 112 Issue: 4 Article Number: 044105 (2012)

Oxygen partial pressure effect on structural and electrical behavior of pulsed laser deposited Zn0.98Co0.02O thin films. K.C. Sekhar, A. Khodorov, A. Chahboun, S. Levichev, A. Almeida, J. Agostinho Moreira, Koppole Kamakshi, C.J.R. Silva, M. Pereira, M.J.M. Gomes. Materials Chemistry and Physics 135, 174 (2012).

Temperature dependence of the electrical conductivity of vapor grown carbon nanofiber/epoxy composites with different filler dispersion levels. P. Cardoso, J. Silva, J. Agostinho Moreira, D. Klosterman, F.W.J. van Hattum, R. Simoes, S. Lanceros-Mendez. Physics Letters A 376, 3290 (2012).

Structural and insulator-to-metal phase transition at 50 GPa in GdMnO3, Oliveira, J., Moreira, J. Agostinho, Almeida, A., Rodrigues, V. H., Costa, M. M. R., Bouvier, P., Guennou, M., Kreisel, J., PHYSICAL REVIEW B Volume: 85 Issue: 5 Article Number: 052101 (2012)

Polar behaviour induced by lithium in potassium tantalate ceramics, Tkach, A., Almeida, A., Moreira, J. Agostinho, Chaves, M. R., Espinha, A., Vilarinho, P. M., JOURNAL OF PHYSICS-CONDENSED MATTER Volume: 24 Issue: 4 Article Number: 045906 (2012)

Synchrotron radiation experiments on multiferroic, magnetocaloric and magnetic nanostructured materials, M. P. Fernández-Garcia, J. Agostinho Moreira, A. M. Pereira, G. N. P. Oliveira, J. Azevedo, J. Oliveira, M. R. Chaves, D. Mota, C. T. Sousa, J. M. Teixeira, A. M. L. Lopes, M. M. R Costa, J. S. Amaral, T. M. Mendonça, V. A. Khonchenko, V. H. Rodrigues, P. B. Tavares, A. Mendes, J. G. Correia, V. S. Amaral, A. Almeida, J. B. Sousa, J. P. Araújo, Ciência & Tecnologia dos Materiais, 24(3/4) (2012) 128.

The role of sucrose in amino polymers synthesized by the strongly acid process. Nuno A. Costa, João Pereira, João Ferra , Paulo Cruz , J. Agostinho Moreira, Jorge Martins, Fernão D. Magalhães, Adélio Mendes, Luísa H. Carvalho. Journal of Adhesion Science and Technology, Volume 27, Issue 7, 2013.

Dispersion of graphene nanoplatelets in poly(vinyl acetate) latex and effect on adhesive bond strength. Artur M. Pinto, Jorge Martins, J. Agostinho Moreira, Adélio M. Mendes and Fernão D. Magalhães. Polymer International, Volume 62, Issue 6, pages 928–935, June 2013.

Room temperature structure and multiferroic properties in Bi0.7La0.3FeO3 ceramics. T.T. Carvalho, J.R.A. Fernandes , J. Perez de la Cruz , J.V. Vidal, N.A. Sobolev , F. Figueiras, S. Das, V.S. Amaral, A. Almeida, J. Agostinho Moreira, P.B. Tavares. Journal of Alloys and Compounds, Volume 554, 25 March 2013, Pages 97–103.

Influence of diffusion parameters on the spectral characteristics of Raman modes of Ti:LiNbO3 planar waveguides. J. M. M. M. de Almeida and J. Agostinho Moreira. Spectroscopy Letters: An International Journal for Rapid Communication, Volume 46, Issue 6, 2013.

Two Experimental Approaches of Looking at Buoyancy, J. Agostinho Moreira, A. Almeida, P. Simeão Carvalho, THE PHYSICS TEACHER, Vol. 51, 476 (2013) .

Effects of oxygen partial pressure on the ferroelectric properties of pulsed laser deposited Ba0.8Sr0.2TiO3 thin films, J.P.B. Silva, K.C. Sekhar, A. Almeida, J. Agostinho Moreira, M. Pereira, M.J.M. Gomes, Applied Physics A, DOI 10.1007/s00339-013-7602-x (2013).

Effect of bi-layer ratio in ZnO/Al2O3 multilayers on microstructure and functional properties of ZnO nanocrystals embedded in Al2O3 matrix, K.C. Sekhar, S. Levichev, M. Buljan, S. Bernstorff, Koppole Kamakshi, A. Chahboun, A. Almeida, J. Agostinho Moreira, M. Pereira, M.J.M. Gomes, Appl Phys A

DOI 10.1007/s00339-013-7809-x (2013).

Influence of laser repetition rate on ferroelectric properties of pulsed laser deposited BaTiO3 films on platinized silicon substrate, J. P. B. Silva, K. C. Sekhar, A. Almeida, J. Agostinho Moreira, M. Pereira, M. J. M. Gomes, Applied Physics A, November 2013, Volume 113, Issue 2, pp 379-384.

Competing exchanges and spin-phonon coupling in Eu1-xRxMnO3 (R=Y, Lu), D. A. Mota, Y. Romaguera Barcelay, P. B. Tavares, M. R. Chaves, A. Almeida, J. Oliveira, W. S. Ferreira, J. Agostinho Moreira, Journal of Physics: Condensed Matter, 25 (2013) 235602.

Induced polarized state in intentionally grown oxygen deficient KTaO3 thin films, D. A. Mota, Y. Romaguera-Barcelay, A. Tkach, J. Pérez de la Cruz, P. M. Vilarinho, P. B. Tavares, J. Agostinho Moreira, A. Almeida, Journal of Applied Physics, 114(3) (2013) 034101.

Influence of process parameters on the RF Sputtered GaP thin films, D. A. Mota, G. Hema Chandra, J. Ventura, A. Guedes, J. Pérez de la Cruz, Journal of Materials Science & Technology, 29(9) (2013) 821.

Ondas e Meios Contínuos, J. Machado da Silva, J. Moreira e J. Oliveira, in-press, UPorto editorial (2013).

Tackling polar response in oxygen deficient KTaO3 thin films, D. A. Mota, Y. Romaguera-Barcelay, A. Tkach, J. Pérez de la Cruz, P. M. Vilarinho, P. B. Tavares, J. Agostinho Moreira and A. Almeida, Accepted to be published in Ferroelectrics (2013).