MAGNETIC BREAKDOWN AND THE SPIN-SPLIT CONDUCTION BAND IN MERCURY - MANGANESE-SELENIDE AND MERCURY-IRON-SELENIDE

New measurements of the anomalous magnetic field dependence in the amplitude of the oscillatory magnetoresistance (Shubnikov-de Haas effect) of n-type HgSe and Hg(,1-x)Mn(,x)Se at liquid helium temperatures are presented. These data are interpreted by use of a closed-orbit magnetic breakdown model which permits Fermi-surface parameters of interest to be determined. It is found that the addition of 0.1 at.% Mn to HgSe results in a Fermi surface whose shape is temperature dependent. Investigation of Hg(,1-x)Fe(,x)Se for x(TURN)2% also shows a temperature dependent Fermi surface