1. MAP – FIS 2011/2012 Universidade do Minho, MAP-FIS Conf. Overview Advanced materials science MAP-FIS conference Session

2. MAP – FIS 2011/2012 Universidade do Minho, MAP-FIS Conf. - Multiferroic materials - Magnetocaloric - Nanowires/nanotubes (magnetic, for photoelectrochemical water splitting) - Quantum dots Preparation techniques: - Templated growth - Electodeposition - Others Applications Presentations

3. MAP – FIS 2011/2012 Universidade do Minho, MAP-FIS Conf. Nanowires/Nanofibres/Nanotubes Wide range of application: - Sensors, nanodevices, magnetic storage - Tissue engineering - Biodevices and systems, nanomedicine - Fundamental studies of cell biology (role of cell nanostructures in guiding cell behavior) - Optics (e.g., metamaterials)

4. MAP – FIS 2011/2012 Universidade do Minho, MAP-FIS Conf. Top-down -Top-down - Litography -e.g., focused ion-beam miling (FIB) - e.g., electron-beam direct writing FIBEBDW

5. MAP – FIS 2011/2012 Universidade do Minho, MAP-FIS Conf. Self-assembled porous templates J. Vac. Sci. Technol. B Porous Al 2 O 3 template Porous templates: - self-organized pores - Block copolymers - Anodic Aluminum oxide (Al 2 O 3 ) Porous alumina (anodic aluminum oxide) templates: - controllable pore diameter - narrow pore size distribution - self-ordered honeycomb lattice of nanopores after a two-step anodization process - Pore diameters of 11 nm and periods of 40 nm (or more) have been achieved Electrodeposition - DC or pulsed (smaller particles) - Able to coat non-flat surfaces Polycyclohexylethylene (PCHE) diblock co-polymer template Chem. Mater.

6. MAP – FIS 2011/2012 Universidade do Minho, MAP-FIS Conf. Electrophoretic Deposition p-Si(001) Si/SiO 2 /TiO 2 /Pt 25V 20mm - Suspension of charged particles - Electric field applied to electrodes - Particles are deposited on the substates - Controled particle sizes. They can be very small (~30 nm or less) - Functional thin films -Can be applied with different materials and combinations of materials - Able to form films on a wide range of shapes and 3D complex and porous structures - It is able to be scaled-up to large volumes and sizes

7. MAP – FIS 2011/2012 Universidade do Minho, MAP-FIS Conf. Nanocontacts - Pt nanocontacts for nanocapacitors - Electrochemically deposited BaTiO 3 Science Pt nanowires Lower electrode 0.2  m

8. MAP – FIS 2011/2012 Universidade do Minho, MAP-FIS Conf. PZT nanocapacitors M. Alexe, et al, Advanced Materials film-type (with top nanocontacts) island-type Nanocapacitors Nano-capacitors for integrated electronics

9. MAP – FIS 2011/2012 Universidade do Minho, MAP-FIS Conf. Biomimetic cilia -Sensing sound (acoustic) - Fluid flow Silicon-nitride suspending membranes with polymer cilia on top Electrodes on membrane and substrate form a variable capacitor for readout Nanowires - Biomimetic Journal of Bionic Engineering

10. MAP – FIS 2011/2012 Universidade do Minho, MAP-FIS Conf. Magnetic nanowires - Patterned arrays - Information storage (high density) - Biological applications (e.g., magnetic carrier to manipulate functionalized particles in suspensions) - Magneto-optical - High-aspect ratio wires through anodic aluminum oxide templates (up to 50  m long) - Magnetic anisotropy studies Nanowires - Magnetic Array of Fe nanowires 200nm diam, 10  m long Nanotechnology Ni nanowires λ laser =632.8 nm

11. MAP – FIS 2011/2012 Universidade do Minho, MAP-FIS Conf. Magnetocaloric Materials - Magnetocaloric effect - Changing magnetic fields induces changes in the materials temperature - Magnetic refrigeration

12. MAP – FIS 2011/2012 Universidade do Minho, MAP-FIS Conf. Magnetocaloric Materials Entropy: Magnetocaloric effect - Application of a magnetic field H -> magnetic material is heated - Reversible process (cooled upon H removal) - Change in magnetic entropy Effect is higher near Tc AdiabaticIsothermal

13. MAP – FIS 2011/2012 Universidade do Minho, MAP-FIS Conf. Magnetocaloric Materials Giant magnetocaloric effect - Strong changes in entropy near Tc - First order magnetic phase transition - e.g., Gd 5 Si 2 Ge 2 5Tesla Gd 5 Si 2 Ge 2 V.K. Pecharsky, Phys. Rev. Lett. (1997) Gd 5 Si 2 Ge 2 : PM->F(I) at T~300K (2 nd order); F(I)->F(II) at T ~ 277 K (1 st order); Magneto-structural (~282-289K) M (emu/g

14. MAP – FIS 2011/2012 Universidade do Minho, MAP-FIS Conf. Magnetocaloric Materials Applications - Magnetic refrigeration -e.g., cooling integrated circuits - avoids fans and complex dissipators - compact and fully solid-state -New materials to: - widen the applicable temperatures - use of lower magnetic fields

15. MAP – FIS 2011/2012 Universidade do Minho, MAP-FIS Conf. Magnetocaloric Materials Other effects for cooling - Magnetic field dependant thermal conductivity - Application of magnetic field increases K 1 and decreases K 2 (changing heat transfer) - Avoids refrigeration fluids completely - e.g., LaCaMnO 3 (K = 0.125 W/mK (0T), 0.085 W/mK (8T) Science PZT Giant electrocaloric effect In ferroelectric materials K 1 < K 2 K 1 +  K 1 > K 2 -  K 2 K 1 -> K 2 ->

16. MAP – FIS 2011/2012 Universidade do Minho, MAP-FIS Conf. Multiferroic Materials Multiferroic materiais combine, at least, two ferroic orders: -Ferroelectricity -Ferromagnetism -Ferroelasticity Some insulator oxides Magnetoelectric materials exhibit a coupling between their electric and magnetic degrees of freedom

17. MAP – FIS 2011/2012 Universidade do Minho, MAP-FIS Conf. Multiferroic Materials The magnetoelectric response (ME), in multiferroic (MF) systems: -appearance of an electric polarization (P) upon applying a magnetic field (H) - and/or appearance of a magnetization (M) upon applying an electric field (E) - Single phase - Composites -> coupling through strain Free energy Polarization Magnetization  ij – induction of a polarization (magnetization) due to a magnetic (electric) field. Linear ME effect

18. MAP – FIS 2011/2012 Universidade do Minho, MAP-FIS Conf. Multiferroic Materials Potencial applications: -magnetic field sensors, current measurement probes, transducer, filters, oscillators, phase shifters, memory devices - Higher ME on laminated composites Sensitive to low H freq. ac fields Tunable microwave line

19. MAP – FIS 2011/2012 Universidade do Minho, MAP-FIS Conf. Multiferroic Materials Single-phase multiferroics - limitation of single-phase materials -> search new materials, Or -> strain coupling ME -> composites - ferroelectricity and magnetism have independent sources with some coupling between them - ferroelectricity typically appears at higher temperatures than magnetism - perovskyte type ferroelectrics, charge-ordering, tilting of unit cell blocks - spontaneous polarization P is often large (10 – 100  C/cm 2 ) - e.g., BiFeO 3 (T FE ~1100K, T N = 643 K, P ~ 90  C/cm 2 ); YMnO 3 (T FE ~914K, T N = 76 K, P ~ 6  C/cm 2 ) Type I Type II Off-centering Charge-ordering tilt Lone pair Spiral magnetic phase - magnetism causes ferroelectricity, implying a strong coupling between them - polarization in these materials is usually much smaller ( ~ 10 -2  C/cm 2 ) - e.g., TbMnO 3, Ni 3 V 2 O 6, or MnWO 4

20. MAP – FIS 2011/2012 Universidade do Minho, MAP-FIS Conf. Piezoelectric Phase + Magnetostrictive Phase Magnetoelectric (ME) response Elastic interactions Multiferroic composites 2-2 multilayer0-3 granular1-3 vertical - Laminated composites – high ME response - Thin films - When a magnetic field is applied to the composite, the magnetic phase changes its shape magnetostrictively. Strain is then passed along to the piezoelectric phase, resulting in an electric polarization. For the converse effect a similar coupling is obtained.

21. MAP – FIS 2011/2012 Universidade do Minho, MAP-FIS Conf. Piezoelectric Phase + Magnetostrictive Phase Magnetoelectric (ME) response Elastic interactions Multiferroic composites Advantages - High magnetization and electric polarization - Higher ME response as compared with single phase

22. MAP – FIS 2011/2012 Universidade do Minho, MAP-FIS Conf. Multiferroic nanostructures Motivation: - on nanostructures high electric fields can be applied with small voltages - energy consumption Magnetoresistance Electroresistance (bias E-field) Materials Science and Engineering R

23. MAP – FIS 2011/2012 Universidade do Minho, MAP-FIS Conf. -Feixe laser, pulsado, incide no alvo. -Radiação laser é absorvida pela superfície sólida do alvo e a energia electromagnética é convertida em energia térmica, causando assim a evaporação explosiva, ou seja a “pluma”. -No interior da pluma, o livre percurso médio é pequeno e, como tal, logo depois da irradiação do laser no alvo a pluma rapidamente se expande sob a forma de um jacto que é perpendicular ao alvo. - As partículas são recolhidas num substrato de modo a formar um filme. Depende da distância alvo-substrato, e da posição da pluma em relação ao substrato. Pulsed laser ablation (PLD)

24. MAP – FIS 2011/2012 Universidade do Minho, MAP-FIS Conf.  Self-assembled magnetoelectric nanostructures - Imiscible materials - Matrix: Piezoelectric. P, E. - Colums: Magnetostrictive. M, H. - Stress mediated coupling => P versus H. M versus E - Laser ablation Zheng et al., Science, (2004) Multiferroic Nanostructures -Others: BaTiO 3 /NiFe 2 O 4, PZT/BaTiO 3 /CoFe 2 O 4, etc BaTiO 3 /CoFe 2 O 4

25. MAP – FIS 2011/2012 Universidade do Minho, MAP-FIS Conf. Multiferroic Nanostructures Magnetic thin film on a piezoelectric substrate - R(1-x)A(x)MnO 3 Manganite films - Strain: changes Mn-O bond-lenghts and Mn-O-Mn angles - Mismatch with substrate affects: structural (unit cell distortion), electrical (metallic phase) and magnetic properties (anisotropy, Tc changes) - CMR tuning and CO-melting - e.g., LaCaMnO 3 /PMN-PT, LaSrMnO 3 /LiNbO 3 Phil. Mag.

26. MAP – FIS 2011/2012 Universidade do Minho, MAP-FIS Conf.  Granular magnetoelectric thin films and composites - Magnetostrictive grains in a piezo matrix -Matrix: Piezoelectric. P, E. - Grains: Magnetostrictive. M, H. - 0-3 composite Multiferroic Nanostructures - e.g., BaTiO 3 /CoFe 2 O 4, PZT/NiFe 2 O 4 C.W. Nan, (1994) BaTiO 3 /CoFe 2 O 4 f CFO = 0.8

27. MAP – FIS 2011/2012 Universidade do Minho, MAP-FIS Conf. PZT-CoFe 2 O 4 nanocomposites ACS Nano NanodotsNanograins inside a Matrix Multiferroic nanostructures

28. MAP – FIS 2011/2012 Universidade do Minho, MAP-FIS Conf. Conclusions - New materials - Combination of different physical properties and techniques - Modeling physical behavior - New designs for applications

29. MAP – FIS 2011/2012 Universidade do Minho, MAP-FIS Conf. 15:45 Probing Electrostructural Coupling on Magnetoelectric CdCr 2 S 4 Speaker: Gonçalo Oliveira 16:00 Effect of la substitution on Tb5Si2Ge2 compound: structural and magnetic properties Speaker: João Horta Belo 16:15 - 17:00 Coffee Break + Poster Session 17:00 Ordered arrays of electrodeposited nanowires and nanotubes: comparing magnetic properties Speaker: Mariana Proença 17:15 Hematite nanowires for solar water splitting: development and structure optimization Speaker: João Azevedo 17:30 Critical behaviour of a three-dimensional hardcore cylinders composite system Speaker: Jaime Silva 17:45 Dynamic electronic interactions at nanoscopic scale Speaker: Marcelo Barbosa 18:00 Exchange coupled donor dimers in nanocrystal quantum dots Speaker: António José Almeida Session