The discovery of ferromagnetism in two-dimensional (2D)
monolayers
has stimulated growing research interest in both spintronics and material
science. However, these 2D ferromagnetic layers are mainly prepared
through an incompatible approach for large-scale fabrication and integration,
and moreover, a fundamental question of whether the observed ferromagnetism
actually correlates with the 2D crystalline order has not been explored.
Here, we choose a typical 2D ferromagnetic material, Fe3GeTe2, to address these two issues by investigating its
ferromagnetism in an amorphous state. We have fabricated nanometer
thick amorphous Fe3GeTe2 films approaching the
monolayer thickness limit of crystallized Fe3GeTe2 (0.8 nm) through magnetron sputtering. Compared to crystallized
Fe3GeTe2, we found that the basic ferromagnetic
attributes, such as the Curie temperature which directly reflects
magnetic exchange interactions and local anisotropic energy, do not
change significantly in the amorphous states. This is attributed to
the short-range atomic order, as confirmed by valence state analysis,
being almost the same for both phases. The persistence of ferromagnetism
in the ultrathin amorphous counterpart has also been confirmed through
magnetoresistance measurements, where two unconventional switching
dips arising from electrical transport within domain walls are clearly
observed in the amorphous Fe3GeTe2 single layer.
These results indicate that the long-range ferromagnetic order of
crystallized Fe3GeTe2 may not correlate to the
2D crystalline order, and the corresponding ferromagnetic attributes
can be utilized in an amorphous state which suits large-scale fabrication
in a semiconductor technology-compatible manner for spintronics applications.