  This paper reports on the improvement of the differential current gain in the
spin-torque transistor based on two independent innovations, viz.the use of
magnetic insulators and the spin Hall effect. Since, except for a few examples,
spin transistors lack the current gain that is essential for many applications,
spintronics and magnetic information technology lack an essential functionality
compared to CMOS devices. Here, we show that negative differential resistance
and large differential gain is possible in a large region of parameter space of
the spin torque transistor. We also demonstrate that functionality is preserved
when the control part is replaced by a normal metal film with a large spin Hall
angle.
