Single crystals of -phase material were grown by means of chemical vapor transport and were investigated by using electron paramagnetic resonance techniques. Most of the observed paramagnetic centers could be explained as arising from 3d transition metals (Cr, Mn, Co, Ni), each with an 8-fold Si coordination. All of the centers appeared to have orthorhombic symmetry and to possess a spin, S = 1/2, which could be explained by the electronic configuration of the impurities when they replaced Fe on its 2 inequivalent lattice sites. The electron paramagnetic resonance data of the single crystals were used to simulate the powder spectra of ceramics. It was concluded that the resonances in the ceramics were much more likely to arise from the Fe-group impurities than from intrinsic defects, as had originally been assumed.

K.Irmscher, W.Gehlhoff, Y.Tomm, H.Lange: Materials Science Forum, 1995, 196-201, 389-94