  Spatially separating electrons of different spins and efficiently generating
spin currents are crucial steps towards building practical spintronics devices.
Transverse magnetic focusing is a potential technique to accomplish both those
tasks. In a material where there is significant Rashba spin-orbit interaction,
electrons of different spins will traverse different paths in the presence of
an external magnetic field. Experiments have demonstrated the viability of this
technique by measuring conductance spectra that indicate the separation of
spin-up and spin-down electrons. However the effect that the geometry of the
leads has on these measurements is not well understood. We show that a
trumpet-like shape opening for the leads offers better resolution of features
in the conductance spectra than other shapes, and demonstrate that this
resolution depends strongly on the width of the leads. Furthermore, the width
of the leads affects the ratio between the amplitudes of the spin-split peaks
in the spectra, by changing the number of subbands occupied by the electrons.
We simulated devices with disorder and observed that this ratio between the
amplitudes of the spin-split peaks is also affected by disorder. Ultimately
careful choice and characterisation of device geometry is crucial for correctly
interpreting the results of transverse magnetic focusing experiments.
