This thesis describes the development of an automatic diameter control system for a Czochralski crystal puller in which the torque on the crystal as it revolves in the melt is monitored and stabilised through changes in the melt temperature. The development of a torque magnetometer of new design having a high linearity and absolute accuracy is also described. The on-line analysis of data produced by the torque magnetometer has yielded precise values for the magnetocrystalline anisotropy of cobalt (grown by Czochralski and other techniques). The magnetometer has also been used for investigations of the magnetocrystalline anisotropy of the terbium/gadolinium alloys. In both cases the compatibility of the observed temperature dependences of the anisotropy with particular models is investigated
