  By calculating orbitally resolved Pauli susceptibilities within maximally
localized Wannier orbital basis transformed from first principles band
structures, we find that magnetism in Fe$_{1+x}$Te still has its itinerant
origin even without Fermi surface nesting, provided orbital modulation of
particle-hole excitations are considered. This leads to strong magnetic
instabilities at wave vector (0,$\pi$)/($\pi$,0) in d$_{xz}$/d$_{yz}$ orbitals
that are responsible for the bicollinear antiferromagnetic state as extra
electrons donated from excess Fe are considered. Magnetic exchange coupling
between excess Fe and in-plane Fe further stabilizes the bicollinear
antiferromagnetic order. Our results reveal that magnetism and
superconductivity in iron chalcogenides may have different orbital origin, as
Pauli susceptibilities of different orbitals evolve differently as a function
of concentration of excess Fe and height of the chalcogen atom measured from
the iron plane.
