Results on the growth of GaAs single crystals by the vertical gradient freeze technique with a rotating magnetic field (RMF) are presented for the first time. The experiments were aimed at influencing the heat flux at the solid-liquid interface in a predefined way, to reduce its curvature. Si-doped. crystals with a diameter of 2 in were grown. Variation of the heat flux is evaluated from dopant striations artificially produced by means of pulses of the RMF itself. The results are compared to those obtained by global modelling of the furnace as. well as by analytical and numerical calculation of the melt flow. The concave deflection of the interface is found to decrease considerably under forced convection, and at a certain aspect ratio a w-shape is observed. The RMF-induced variation of local growth velocity is measured. The experimental results agree well with the numerical computations. (C) 2002 Elsevier Science B.V. All rights reserved.