  Growth parameters play a significant role in the crystal quality and physical
properties of layered materials. Here we present a case study on a van der
Waals magnetic NbFeTe2 material. Two different types of polymorphic NbFeTe2
phases, synthesized at different temperatures, display significantly different
behaviors in crystal symmetry, electronic structure, electrical transport, and
magnetism. While the phase synthesized at low temperature showing behavior
consistent with previous reports, the new phase synthesized at high
temperature, has completely different physical properties, such as metallic
resistivity, long-range ferromagnetic order, anomalous Hall effect, negative
magnetoresistance, and distinct electronic structures. Neutron diffraction
reveals out-of-plane ferromagnetism below 70K, consistent with the electrical
transport and magnetic susceptibility studies. Our work suggests that simply
tuning synthetic parameters in a controlled manner could be an effective route
to alter the physical properties of existing materials potentially unlocking
new states of matter, or even discovering new materials.
