  There is currently much interest in materials and structures that provide
coupled ferroelectric and ferromagnetic responses, with a long-term goal of
developing new memories and spintronic logic elements. Within the field there
is a focus on composites coupled by magnetostrictive and piezoelectric strain
transmitted across ferromagnetic-ferroelectric interfaces, but substrate
clamping limits the response in the supported multilayer configuration favoured
for devices. This constraint is avoided in a ferroelectric-ferromagnetic
bilayer in which the magnetic response is modulated by the electric field of
the poled ferroelectric. Here, we report the realization of such a device using
a diluted magnetic semiconductor (DMS) channel and a polymer ferroelectric
gate. Polarization reversal of the gate by a single voltage pulse results in a
persistent modulation of the Curie temperature as large as 5%. The device
demonstrates direct and quantitatively understood electric-fieldmediated
coupling in a multiferroic bilayer and may provide new routes to nanostructured
DMS materials and devices via ferroelectric domain nanopatterning. The
successful implementation of a polymer-ferroelectric gate fieldeffect
transistor (FeFET) with a DMS channel adds a new functionality to semiconductor
spintronics and may be of importance for future low-voltage spintronics devices
and memory structures.
