MATERIALSthe similar nitronyl nitroxide radicals NITPh and The interactions between these two spin densities of opposite sign can therefore be considered to give rise to the required ferromagnetic inter-plane couplings.In conclusion we have presented evidence of a ferromagnetic transition in the nitronyl nitroxide NIT(SMe)Ph. The diffuse electronic cloud of the sulfur atom in the radical substituent generates sufficiently strong ferromagnetic interactions even at large distances. It may be hoped that on finding radicals with more favorable packing higher critical temperature can be achieved. ( VCH Verlug.gewllschuft mhH, 0-69469 Wrmham, 1995 O935-9648/95/O505-O4XO $ 5 00+ 2510 Adv Mawr 1995 7, No 5

The first reported use of tri-isopropyl gallium (TiPGa) in chemical beam epitaxy (CBE) is described. Hall measurements performed on the resulting undoped GaAs epitaxial layers indicate an order of magnitude reduction in unintentional carbon impurity levels compared to structures grown under comparable conditions using the standard CBE precursor, triethyl gallium. 2 K photoluminescence spectra match those recorded elsewhere from state-of-the-art high purity GaAs material grown by molecular beam epitaxy, and 77 K Hall measurements on intentionally n-type doped GaAs layers confirm residual acceptor levels in the low 1014 cm−3 range. The early data obtained already provide a clear indication of the important potential of TiPGa as an improved precursor for the CBE growth of Ga-containing III–V materials.

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