Ordering classification of columnar lattices formed in magnetic fluid subjected to perpendicular fields

When the thin film of high-quality magnetic fluid is subjected to a perpend icular magnetic field, a separation of particles from the liquid matrix wil l occur, leading to a phase transition with a phase that is concentrated in particles separating from a dilute phase. The concentrated phase makes up the cylindrical columns that can form two-dimensional lattices. We have exp lored the field-induced lattices with optical microscopy, digital imaging a nd computer-video techniques in this study, to classify the ordering proper ty in terms of bond-orientation order. (C) 2001 Elsevier Science B.V. All r ights reserved.