In this thesis I describe a sensitive technique for quantifying the chemical potential anisotropy of magnetically ordered and spin-orbit coupled materials. An aluminium single electron transistor (SET) lithographically fabricated on top of a magnetic gate is used to characterise the chemical potential anisotropy of Ga0 .97Mno. 03As and Gao.941\1no.o6As. The conductance variation of the SET provides a direct probe of the magnetisation-dependent change in the chemical potential of the magnetic gate with ?eV resolution. The control of the SET conductance by the magnetisation direction of the gate opens the way to a new recording mechanism. Achieving the same control in a semiconductor device represents a first step towards possible applications in computer memories. In the second part of my work I present the measurements on a CoPt gated metal-oxide-semiconductor� field effect transistor. In the last part of my thesis, I present a study of the response of a metal SET to a radio-frequency perturbation, which showed the conditions of maximum sensitivity and set a lower limit to the detection bandwidth of the SET. This study is important for assessing the performance of a prototypical device for detecting fast magnetisation switching or for quantifying the chemical potential anisotropy of magnetic nano-structures that cannot be electrically connected to an electrode, but that are still expected to have interesting anisotropic properties