Phase transitions of granular disks with a magnetic dipole
P. Coutiño, N. Ibarra–Ávalos and A. Gil–Villegas*
Department of Physical Engineering, Sciences and Engineering Division, University of Guanajuato, Lomas del Bosque 103, León 37150, Guanajuato, México, *e–mail: gil@fisica.ugto.mx
Recibido el 23 de noviembre de 2009
Aceptado el 14 de octubre de 2010
Abstract
We present a simple experiment to study phase transitions of a granular system composed of disks with a magnetic dipole. The particles are contained within a cylindrical container and are excited through alternating magnetic fields. The initial configuration of this system is a low–density isotropic phase. By increasing the density, a critical value is reached and the system starts to organize into columns. At higher densities an ordered state is obtained where structural columnar patterns are formed. The set up of the experimental device is very easy to implement, using standard high–school and undergraduate physics laboratory facilities. The experiment can be used, combined with computer simulations, to introduce the subject of phase transitions in complex materials.
Keywords: Granular media; liquid crystals; Monte Carlo simulations.
Resumen
Presentamos un experimento simple para estudiar transiciones de fase de sistemas granulares compuestos de discos con un dipolo magnético. Las partículas están contenidas en un recipiente cilíndrico y son excitadas por medio de campos magnéticos alternos. La configuración inicial de este sistema es una fase isotrópica de baja densidad. Al incrementar la densidad se alcanza un valor crítico y el sistema comienza a organizarse en columnas. A densidades mayores se observa un estado ordenado con patrones de orden columnar. El arreglo experimental es muy fácil de implementar, utilizando instalaciones típicas de laboratorios de enseñanza media superior y superior. El experimento se puede utilizar, combinado con resultados de simulación computacional, para introducir el tema de transiciones de fase en materiales complejos.
Descriptores: Medios granulares; cristales líquidos; simulaciones de Monte Carlo.
PACS: 75.70.Kw, 64.70.mf, 64.70.mj
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Acknowledgments
We thank CONACYT (Consejo Nacional de Ciencia y Tecnología México) for financial support (grant 61418) and for a PhD and MSc scholarships (NIA and PC, respectively). The authors would like to thank Enrique González–Tovar (Instituto de Física Universidad Autonoma de San Luis Potosí, México) for useful discussions and suggestions.
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