1. -CoFe 2 O 4 nanocomposite films Magnetic Properties of BaTiO 3 -CoFe 2 O 4 nanocomposite films :::: Grupo FCD :::: Centro de Física da Universidade do Minho :::: Univ. Minho: B.G. Almeida, J.A. Mendes and A.G. Rolo J. Barbosa IFIMUP: J.P. Araújo and J.B. Sousa

2. Introduction Samples Preparation Structural Characterization Magnetic Characterization Conclusions :::: Grupo FCD :::: Centro de Física da Universidade do Minho ::::

3. Introduction Magnetoelectric materials exhibit a coupling between their electric and magnetic degrees of freedom :::: Grupo FCD :::: Centro de Física da Universidade do Minho :::: Piezoelectric Phase + Magnetostrictive Phase The magnetic properties of these nanostructures depend critically on the phase morphology and internal stress distribution Nanostructured composites: Magnetoelectric response Elastic interactions

4. Samples Preparation The BaTiO 3 /CoFe 2 O 4 samples were produced by laser ablation. :::: Grupo FCD :::: Centro de Física da Universidade do Minho :::: Substrates: Si(001) P O2 =1 mbar T Sub = 600ºC Laser: = 248 nm, fluence of 1.5 J/cm 2, 10 Hz repetition rate The ablation targets: Deposition Conditions: CoFe 2 O 4 and BaTiO 3 mixed and compressed powders with CoFe 2 O 4 concentrations: 20%, 30%, 40%, 50%, 60% and 70%.

5. Structural Characterization X-Ray Diffraction: Unit Cell BaTiO 3  Tetragonal CoFe 2 O 4  Inverse Cubic Spinel :::: Grupo FCD :::: Centro de Física da Universidade do Minho ::::

6. Structural Characterization (cont.) Grain Size: CoFe 2 O 4  average grain size approximately constant with increasing CoFe 2 O 4 concentration (~30nm). BaTiO 3  as the concentration of the CoFe 2 O 4 increase, the grain size of the BaTiO 3 phase decreases, from 91.5 nm to 30nm. :::: Grupo FCD :::: Centro de Física da Universidade do Minho ::::

7. Structural Characterization (cont.) Lattice Parameters: :::: Grupo FCD :::: Centro de Física da Universidade do Minho :::: CoFe 2 O 4 Lattice ParameterBaTiO 3 Lattice Parameteres CoFe 2 O 4  compressed related to bulk, stress relaxing with increasing CoFe 2 O 4 concentration BaTiO 3  progressively lattice distortion with the increase of CoFe 2 O 4 concentration

8. Structural Characterization (cont.) Raman Spectroscopy: CoFe 2 O 4 characteristic modes are present :::: Grupo FCD :::: Centro de Física da Universidade do Minho :::: The blue shift in CoFe 2 O 4 modes with CoFe 2 O 4 concentration results from the lattice strain

9. Magnetic Characterization :::: Grupo FCD :::: Centro de Física da Universidade do Minho :::: Magnetic moment increases with increasing cobalt ferrite concentration Hysteresis Cycles:

10. Magnetic Characterization (cont.) The coercivity (Hc) decreases with increasing CoFe 2 O 4 concentration. Hc of small grains (< 40nm in CoFe 2 O 4 )  to magnetocristaline anisotropy. Hc of big grains (> 40nm in CoFe 2 O 4 )  stress. Hc decrease due to the relaxation of the stress in big grains to the increase of small grains agglomeration in bigger polycrystalline clusters :::: Grupo FCD :::: Centro de Física da Universidade do Minho :::: Coercive Field (Hc):

11. Conclusions BaTiO 3 /CoFe 2 O 4 deposited films are polycrystalline and composed by a mixture of tetragonal-BaTiO 3 and CoFe 2 O 4 with the inverse cubic spinel structure. The grain sizes are in the range 30nm to 100nm. CoFe 2 O 4 phase is under compressive stress that relaxes with increasing cobalt ferrite concentration. A decrease of the coercive field with increased CoFe 2 O 4 concentration was observed, due to the relaxation of the stress in the films as well as to the increase of particle agglomeration in bigger polycrystalline clusters with increasing cobalt ferrite concentrations. :::: Grupo FCD :::: Centro de Física da Universidade do Minho ::::

12. End!!! :::: Grupo FCD :::: Centro de Física da Universidade do Minho ::::