  A number of spintronic junction transistors, that exploit the spin degree of
freedom of an electron in addition to the charge degree of freedom, have been
proposed to provide simultaneous non-volatile storage and signal processing
functionality. Here, we show that some of these transistors unfortunately may
not have sufficient voltage and current gains for signal processing. This is
primarily because of a large output ac conductance and poor isolation between
input and output. The latter also hinders unidirectional propagation of logic
signal from the input of a logic gate to the output. Other versions of these
transistors appear to have better gain and isolation, but not better than those
of a conventional transistor. Therefore, these devices may not improve
state-of-the-art signal processing capability, although they may provide
additional functionality by offering non-volatile storage. They may also have
niche applications in non-linear circuits.
