  Carrier-induced ferromagnetic semiconductors (FMSs) have been intensively
studied for decades as they have novel functionalities that cannot be achieved
with conventional metallic materials. These include the ability to control
magnetism by electrical gating or light irradiation, while fully inheriting the
advantages of semiconductor materials such as band engineering. Prototype FMSs
such as (In,Mn)As or (Ga,Mn)As, however, are always p-type, making it difficult
to be used in real spin devices. This is because manganese (Mn) atoms in those
materials work as local magnetic moments and acceptors that provide holes for
carrier-mediated ferromagnetism. Here we show that by introducing iron (Fe)
into InAs, it is possible to fabricate a new FMS with the ability to control
ferromagnetism by both Fe and independent carrier doping. Despite the general
belief that the tetrahedral Fe-As bonding is antiferromagnetic, we demonstrate
that (In,Fe)As doped with electrons behaves as an n-type electron-induced FMS,
a missing piece of semiconductor spintronics for decades. This achievement
opens the way to realise novel spin-devices such as spin light-emitting diodes
or spin field-effect transistors, as well as helps understand the mechanism of
carrier-mediated ferromagnetism in FMSs.
