  Materials with zero energy band gap display intriguing properties including
high sensitivity of the electronic band structure to external stimulus such as
pressure or magnetic field. An interesting candidate for zero energy band gap
are Weyl nodes at the Fermi level EF. A prerequisite for the existence of Weyl
nodes is to either have inversion or time reversal symmetry broken. Weyl nodes
in systems with broken time reversal symmetry are ideal to realize the
tunability of the electronic band structure by magnetic field. Theoretically,
it has been shown that in ferromagnetic Weyl materials, the band structure is
dependent upon the magnetization direction and thus the electronic bands can be
tuned by controlling the magnetization direction. Here, we demonstrate tuning
of the band structure in a kagome Weyl ferromagnetic metal Fe3Sn2 with
magnetization and magnetic field. Owing to spin-orbit coupling, we observe
changes in the band structure depending on the magnetization direction that
amount to a decrease in the carrier density by a factor of four when the
magnetization lies in the kagome plane as compared to when the magnetization is
along the c axis. Our discovery opens a way for tuning the carrier density in
ferromagnetic materials.
