Colloids and Surfaces A: Physicochem. Eng. Aspects 403 (2012) 139–147 Contents lists available at SciVerse ScienceDirect Colloids and Surfaces A: Physicochemical and Engineering Aspects jo ur nal homep a ge: www.elsevier.com/locate/colsurfa The influence of processing parameters on the orientation of barium ferrite platelets during electrophoretic deposition Simona Ovtar a,∗ , Darja Lisjak a , Miha Drofenik a,b a Department for Material Synthesis, Jozef Stefan Institute, Ljubljana, Slovenia b Faculty for Chemistry and Chemical Technology, University of Maribor, Maribor, Slovenia a r t i c l e i n f o Article history: Received 3 January 2012 Received in revised form 21 March 2012 Accepted 6 April 2012 Available online 12 April 2012 Keywords: Electrophoretic deposition Magnetic materials Oriented films Anisotropic grain growth a b s t r a c t Oriented deposits of hard-magnetic barium ferrite were prepared using electrophoretic deposition (EPD). A stable suspension of highly anisotropic particles with diameters of a few 100 nm and thicknesses of 10 nm was prepared in 1-butanol. The electrophoretic velocities for the two orientations of particles with respect to the electrode were calculated. The particles migrated to the electrode with the basal plane perpendicular to the electrode. The oriented deposits were formed under the influence of the hydrodynamic force near the electrode. The sintering was accompanied by an anisotropic and abnormal grain growth and the oriented, larger grains affected most significantly the overall orientation of the films. The grain size was investigated by SEM image analysis and the orientation of the films was calculated from XRD patterns and determined from magnetic measurements. The films with the best orientations were prepared with the lowest applied voltage, where the electrophoretic velocity was the slowest. The films that were prepared with step EPD and sintered at 1150 ◦ C had a remanence-to-saturation magnetization of 0.9. The density of the film and the magnetization values were further increased by iso-static pressing of the deposits before sintering. © 2012 Elsevier B.V. All rights reserved. 1. Introduction Today there is an increasing demand for small electronic devices for use in integrated circuits. The candidates for materials to act as microwave and millimeter-wave absorbers and non-reciprocal devices are hexaferrites in the form of thick films with aligned magnetic moments. Barium ferrite (BaF) is the simplest hexa- ferrite, the basic properties of which enable the operation of non-reciprocal devices in the frequency range around 30–50 GHz. [1] BaF has the chemical formula BaFe 12 O 19 and is a ferrimagnetic material with hard-magnetic properties. It has a high saturation magnetization (72 emu/g for a single crystal) and a high magne- tocrystalline anisotropy field (17 kOe). The crystal structure of BaF is of the magnetoplumbite type and its unit cell is highly anisotropic in the c direction [2]. Particles and grains of BaF typically grow in the shape of thin platelets, with the c axis perpendicular to the basal plane of the platelets. Due to the ordering of the magnetic moments of the iron ions in the crystal structure the total mag- netic moment of the particles coincides with the crystallographic c axis, i.e., the magnetic easy axis. Therefore, the total magnetic ∗ Corresponding author at: Jozef Stefan Institute, Jamova 39, Si-1000 Ljubljana, Slovenia. Tel.: +386 1 477 36 29; fax: +386 1 251 93 85. E-mail address: simona.ovtar@ijs.si (S. Ovtar). moment is perpendicular to the basal plane of the platelet. The thick films of BaF for millimeter-wave non-reciprocal devices, and other devices that operate at the remanence point, must have aligned magnetic moments. For the preparation of films with aligned mag- netic moments, or so-called oriented films, many studies have been carried out [3–5]. A technique that is used for the preparation of thick films and was shown to be successful for the preparation of oriented BaF films is screen printing [6]. To achieve a good enough orienta- tion the deposits were heat treated in an external magnetic field. Another method that can be used for the preparation of oriented thick films from different materials is electrophoretic deposition (EPD) [7–10]. Oriented deposits can be prepared by EPD from a stable suspen- sion without any agglomerates. The presence of agglomerates leads to the preparation of randomly oriented deposits with an inhomo- geneous density. Stable suspensions are most often prepared by adjusting the pH of the suspension to achieve the highest zeta- potential and a high electrostatic repulsion, or by the addition of a surfactant to prevent any attraction between the particles by steric repulsion and/or electrostatic repulsion [11]. However, the prepa- ration of a stable suspension of hard-magnetic particles is a more challenging task. The strong magnetic attraction between these particles must be prevented by a strong electrosteric repulsion. In our previous work [12] we showed that the necessary repulsion between the particles can be ensured by electrosteric repulsion 0927-7757/$ – see front matter © 2012 Elsevier B.V. All rights reserved. http://dx.doi.org/10.1016/j.colsurfa.2012.04.004