  Fe5GeTe2 single crystals can be divided into nonquenched (NQ) and
quench-cooled (QC) phases with different magnetic properties. A comprehensive
understanding of the magnetic property variations in the NQ and QC phases is
imperative for guiding Fe5GeTe2 towards spintronics applications; however, it
remains elusive. Here, we report a real-space study on the structural and
magnetic properties of these two magnetic phases using cryogenic magnetic force
microscopy and scanning tunneling microscopy. The thermal history introduces
disorder and order to the Fe(1) sites, resulting in the NQ and QC phases
exhibiting global and broken inversion symmetry, respectively. The observed
magnetic domain transitions (branching to labyrinthine) in the spin
reorientation process and the distinct 3D spin textures stabilized by magnetic
dipolar interaction observed in field-dependent studies allow the NQ phase to
exhibit a more resilient global magnetic state. In contrast, the QC phase
exhibits enhanced magnetic anisotropy, resulting in a higher TC. Meanwhile, the
Dzyaloshinskii-Moriya interaction (DMI) introduced by the broken inversion
symmetry causes the QC phase to exhibit a localized magnetic state: no domain
transformation occurs during spin reorientation, and irregular domain states
are observed in field-related studies. Our work provides an important reference
for understanding the complex magnetic properties in Fe5GeTe2.
