  We demonstrate electrical control of ferromagnetism in field-effect
transistors with a trilayer quantum well (QW) channel containing an ultrathin
n-type ferromagnetic semiconductor (In,Fe)As layer. A gate voltage is applied
to control the electron wavefunctions {\phi}i in the QW, such that the overlap
of {\phi}i and the (In,Fe)As layer is modified. The Curie temperature is
largely changed by 42%, whereas the change in sheet carrier concentration is 2
- 3 orders of magnitude smaller than that of previous gating experiments. This
result provides a new approach for versatile, low power, and ultrafast
manipulation of magnetization.
