HIGH-FIELD MAGNETIZATION MEASUREMENTS ON ALPHA-(BEDT-TTF)(2)KHG(SCN)(4)

We report torque measurements of the steady and oscillatory magnetization of alpha-(BEDT-TTF)(2)KHg(SCN)(4), where BEDT-TTF is bis(ethylenedithio)tetrathiafulvalene, at temperatures down to 0.4 K in magnetic fields around the magnetic phase transition at 24 T, the so called kink transition. The effective cyclotron mass changes only slightly at the kink transition being m* = m/m(c) = 1.77 (m(c) is the free electron mass) above 24 T and m* approximate to 1.7 at 20 T for a magnetic field perpendicular to the highly conducting ac-plane (Theta = 0 degrees). For Theta = 60.2 degrees we find m* = 3.55 (B approximate to 18 T). In the low field state the amplitude of the oscillatory magnetization (mu(0)M(osc) = 7.5 x 10(-7) T) is small; this corresponds with a high Dingle temperature (3-4 K). At 24 T a strong increase in the oscillation amplitude appears accompanied by a decrease in the Dingle temperature to T-D less than or equal to 2 K. The steady torque shows a quadratic increase with field at low B-values and tends to saturate near the phase transition for small angles Theta. For tilt angles Theta greater than or equal to 60 degrees the typical increase of the de Haas-van Alphen amplitude at the kink transition is no longer observed, but several anomalies occur in the steady torque above 15 T; even at 27 T alpha-(BEDT-TTF)(2)KHg(SCN)(4) is in a complex magnetic groundstate.