  The control of the electron spin by external means is a key issue for
spintronic devices. Using spin- and angle-resolved photoemission spectroscopy
(SARPES) with three-dimensional spin detection, we demonstrate operando
electrostatic spin manipulation in ferroelectric GeTe and multiferroic
Ge1-xMnxTe. We not only demonstrate for the first time electrostatic spin
manipulation in Rashba semiconductors due to ferroelectric polarization
reversal, but are also able to follow the switching pathway in detail, and show
a gain of the Rashba-splitting strength under external fields. In multiferroic
Ge1-xMnxTe operando SARPES reveals switching of the perpendicular spin
component due to electric field induced magnetization reversal. This provides
firm evidence of effective multiferroic coupling which opens up magnetoelectric
functionality with a multitude of spin-switching paths in which the magnetic
and electric order parameters are coupled through ferroelastic relaxation
paths. This work thus provides a new type of magnetoelectric switching
entangled with Rashba-Zeeman splitting in a multiferroic system.
