Field Induced Structural Transition in Mesocrystallites

We have fabricated multiply coated glass spheres with diameters of $45(\pm 2)\mu \mathrm{m}$ that exhibit appreciable magneto-, as well as electrorheological responses. Under crossed electric and magnetic fields, the microspheres were observed to form columnar crystallites with a structure that transforms from body-centered tetragonal to face-centered cubic as the ratio between the magnetic and the electric fields exceeded a minimum value. The observed transition scenario is in excellent agreement with calculations based on the model of field induced crystal formation and structural transition.