Transverse rotating magnetic fields (B-max = 7.5 mT, f(rot) = 50 Hz) were a
pplied to the floating zone growth of doped silicon. Non-periodic dopant fl
uctuations caused by time-dependent thermocapillary convection were conside
rably reduced by the rotating field. The radial segregation profiles (measu
red by a spreading resistance probe) became more homogeneous and more symme
tric. The transition from a regime dominated by time-dependent thermocapill
ary convection to a flow state characterized by the rotating magnetic field
was determined. This threshold depends on the height of the melt as well a
s the melt diameter (crystals between 8 and 14 mm have been investigated) a
nd the efficiency of the applied field increases with larger melt zones. Fo
r a melt of 14 mm in diameter and an aspect ratio of I it is in the range o
f 2.5-3.75 mT/50 Hz (corresponding to a Taylor number of Ta = 9.3 x 10(3) -
2.1 x 10(-4)). The change from a time-dependent 3D-flow without field to a
quasi-axisymmetric 2D-flow with the magnetic field is corroborated by numer
ical simulations of the flow field: the thermocapillary driven irregular fl
ow rolls are transformed to a nearly axisymmetric flow with high azimuthal
flow velocities but reduced axial and radial components. (C) 2001 Elsevier
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