Polarized light transmission in ferrofluids loaded with carbon nanotubes in the presence of a uniform magnetic field C. Vales-Pinzón a,n , J.J. Alvarado-Gil a , R. Medina-Esquivel b , P. Martínez-Torres c a Applied Physics Department, CINVESTAV-Unidad Mérida, Antigua carretera a Progreso km 6, A.P. 73, Cordemex, Mérida Yucatán 97310, Mexico b Facultad de Ingeniería-UADY, Av. Industrias no Contaminantes por Periférico Norte, A.P.150, Cordemex, Mérida, Yucatán, Mexico c Department of Mechanical Engineering, University of California, Riverside, 900 University Ave., Riverside, CA 92521, USA article info Article history: Received 3 April 2013 Received in revised form 17 December 2013 Available online 13 June 2014 Keywords: Magnetic nanoparticle Ferrofluid Carbon nanotube Polarization Optical transmittance abstract Magneto-optic phenomena in ferrofluids have been shown to be related to the formation of chain structures, due to the arrangement of the ferromagnetic particles, induced by an applied magnetic field. In this work, the effects on transmission of polarized light due to anisotropic effects induced by an external magnetic field in ferrofluids with carbon nanotubes are studied. The time response of the system presents two well defined stages, in the first one, which is very short, the fluid behaves as a polarizer. In contrast in the second stage, the effects of light transmission dominate. In this stage the transmitted light intensity grows with time and after a long time reaches a constant stable value. It is shown that these phenomena depend on the carbon nanotubes concentration as well as on the strength of the applied magnetic field. Using a simple model that considers a chain-like structure formation, it is possible to determine the rate of agglomeration of the formed structures and the attenuation coefficient of the transmitted light. The formation of nanostructures leads to variation in the transmitted light, depending on the polarization of the incident light. These magnetic nanostructures can find numerous applications in nanotechnology, optical devices and medicine. & 2014 Elsevier B.V. All rights reserved. 1. Introduction A ferrofluid is a stable colloidal suspension of small ferromag- netic particles, with typical dimensions of the order of 10 nm, suspended in a liquid carrier [1]. The physical properties of these magnetic fluids can be modified in the presence of an external magnetic field. Ferrofluid nanoparticles are superparamagnetic, having the property of being susceptible to become aligned in the direction of an external magnetic field. When this magnetic field is removed, the particles lose their magnetization and return to a random orientation, in a time scale which depends on the physical properties of the fluid and those of the nanoparticles. In the absence of an external magnetic field, the ferrofluid is isotropic. However, when a ferrofluid is exposed to an external magnetic field, it develops optical anisotropy due to the formation of microstructures such as field-induced chains [2]. In recent years, the study of the optical properties of ferrofluids has been of great interest, due to the wide variety of possible applications based on the magneto-optical phenomena. Such is the case of birefringence, dichroism, light scattering, ellipticity and Faraday rotation [3–6]. The behavior of these materials is the basis of the functioning of a variety of optical devices [7]. Optical characterization of these systems has shown that the structure of these systems has a strong dependence on the presence of a magnetic field, and that such behavior evolves in time [8]. For this reason, optical transmission studies of ferrofluid in an applied magnetic field have attracted the attention of diverse research groups [9,10]. The intensity of the light, transmitted through a suspension of nanoparticles of magnetite (Fe 3 O 4 ), shows variations due to the dependence of the optical transmission coefficient with the formation of chains in the suspension. Based on experimental observations of samples with very low concen- tration of particles [11], it has been claimed, from the theoretical point of view, that the time evolution of the agglomeration in structured systems induced by an external field, occurs in two steps, starting with the assembling of chains followed by forma- tion of columns [12]. One of the simplest approaches corresponds to the model of chains, which states that under the action of an applied magnetic field, the particles are magnetized and aligned in the direction and intensity of the applied field [13]. In this approach, it is also shown that the formation of these structures depends on the time interval in which the field is applied [14]. From the microscopic point of view, the particles are placed one after another to form thin linear chains, distributed throughout the sample and oriented in the direction of the applied magnetic field Contents lists available at ScienceDirect journal homepage: www.elsevier.com/locate/jmmm Journal of Magnetism and Magnetic Materials http://dx.doi.org/10.1016/j.jmmm.2014.06.025 0304-8853/& 2014 Elsevier B.V. All rights reserved. n Corresponding author. E-mail address: cvales@mda.cinvestav.mx (C. Vales-Pinzón). Journal of Magnetism and Magnetic Materials 369 (2014) 114–121