  Ferromagnetic transitions between quantum Hall states with different
polarization at a fixed filling factor can be studied by varying the ratio of
cyclotron and Zeeman energies in tilted magnetic field experiments. However, an
ability to locally control such transitions at a fixed magnetic field would
open a range of attractive applications, e.g. formation of a reconfigurable
network of one-dimensional helical domain walls in a two-dimensional plane.
Coupled to a superconductor, such domain walls can support non-Abelian
excitation. In this article we report development of heterostructures where
quantum Hall ferromagnetic (QHFm) transition can be controlled locally by
electrostatic gating. A high mobility two-dimensional electron gas is formed in
CdTe quantum wells with engineered placement of paramagnetic Mn impurities.
Gate-induced electrostatic field shifts electron wavefunction in the growth
direction and changes overlap between electrons in the quantum well and d-shell
electrons on Mn, thus controlling the s-d exchange interaction and the field of
the QHFm transition. The demonstrated shift of the QHFm transition at a filling
factor $\nu=2$ is large enough to allow full control of spin polarization at a
fixed magnetic field.
