  In this work, we reported the observation of a novel planar topological Hall
effect (PTHE) in single crystal of Fe3GeTe2, a paradigmatic two-dimensional
ferromagnet with strong uniaxial anisotropy. The Hall effect and
magnetoresistance varied periodically when the external magnetic field rotated
in the ac (or bc) plane, while the PTHE emerged and maintained robust with
field swept across the hard-magnetized ab plane. The PTHE covers the whole
temperature region below Tc (~150 K) and a comparatively large value is
observed at 100 K. Emergence of an internal gauge field was proposed to explain
the origin of this large PTHE, which is either generated by the possible
topological domain structure of uniaxial Fe3GeTe2 or the non-coplanar spin
structure formed during the in-plane magnetization. Our results promisingly
provide an alternative detection method to the in-plane skyrmion formation and
may bring brand-new prospective to magneto-transport studies in condensed
matter physics.
