Angular dependence of the high field phase transition in /spl alpha/-(BEDT-TTF)/sub 2/T1Hg(SCN)/sub 4/

Summary form only given. We report results of a systematic inagnetoresistance study of the quasi-two dimensional (Q2D) organic conductor /spl alpha/-(BEDT-TTF)/sub 2/T1Hg(SCN)4 as a function of angle in fields up to 30 tesla. The high field phase transition, or kink field present in this material and characterized by a sudden drop in magnetoresistance, is mapped out as a function of /spl phi/ defined to be the angle between the magnetic field and the normal to the highly conducting Q2D planes. This transition occurring at 25 tesla for /spl phi/ = 0, is observable for angles /spl phi/ < 65, above which it either does not exist or is above field range. These results are further elucidated through fixed field angle sweeps. In this case angular magnetoresistance oscillations (AMRO) characterized by sharp minima appear below the transition, while Yamaji type oscillations appear above. The transition between these two effects clearly identifies the H-/spl phi/ kink field boundary. Additional features such as Shubnikov-de Haas (SdH) oscillations and the magnetoresistance maximum (Hmax) are mapped as a function of angle. The origin of these angular dependent magnetoresistance features is discussed based upon current Fermi surface models for the /spl alpha/-(BEDT TTF)2MH9(SCN)4 (M = K, Rb, TI) family.