Radio-frequency mu SR investigations on paramagnetic muonium centres in crystalline silicon

Radio frequency (RF) muon-spin resonance (RF mu SR) experiments on the para magnetic muonium centres Mu(T) (muonium located at tetrahedral sites) and M u(BC) (bond-centred muonium), present in crystalline silicon, were carried out at applied magnetic fields B-0 up to 6 mT and a constant irradiated fre quency nu(RF) of approximately 80 MHz. In the magnetic-held dependence of t he RF asymmetry a(RF), i.e, the RF induced change of the muon-decay asymmet ry, two resonances were observed, one corresponding to Mu(T), the other to Mu(BC). Systematic RF mu SR measurements were performed on intrinsic silico n single crystals grown by the Czochralski method (oxygen concentration 2 x 10(17) cm(-3)) and the float-zone method (oxygen concentration < 10(15) cm (-3)). No Mu(T) signal has been observed in transverse field (TF) mu SR. be low T = 50 K in the Czochralski-grown sample whereas a Mu(T) signal was fou nd with RF mu SR. This RF mu SR result proves that the Mu(T) species in thi s sample undergo dynamic processes, in which presumably oxygen is involved. (C) 2000 Elsevier Science B.V. All rights reserved.