  The interplay between electronic eigenstates, spin, and orbital degrees of
freedom, combined with fundamental breaking of symmetries is currently one of
the most exciting fields of research. Multiferroics such as (GeMn)Te fulfill
these requirements providing unusual physical properties due to the coexistence
and coupling between ferromagnetic and ferroelectric order in one and the same
system. Here we show that multiferroic (GeMn)Te inherits from its parent
ferroelectric {\alpha}-GeTe compound a giant Rashba splitting of
three-dimensional bulk states which competes with the Zeeman spin splitting
induced by the magnetic exchange interactions. The collinear alignment of
ferroelectric and ferromagnetic polarization leads to an opening of a tunable
Zeeman gap of up to 100 meV around the Dirac point of the Rashba bands, coupled
with a change in spin texture by entanglement of magnetic and spin-orbit order.
Through applications of magnetic fields, we demonstrate manipulation of spin-
texture by spin resolved photoemission experiments, which is also expected for
electric fields based on the multiferroic coupling. The control of spin
helicity of the bands and its locking to ferromagnetic and ferroelectric order
opens fascinating new avenues for highly multifunctional multiferroic Rashba
devices suited for reprogrammable logic and/or nonvolatile memory applications.
