Exchange bias effect in the total two-dimensional van der Waals heterostructures of Fe5−xGeTe2/CrPS4

Abstract

We construct vertically stacked van der Waals (vdWs) heterostructures using two-dimensional (2D) ferromagnetic (FM) metal Fe5−xGeTe2 (20 nm ≤ t ≤ 90 nm) nanoflakes with a strong perpendicular magnetic anisotropy (PMA) and ∼60 nm thick A-type antiferromagnetic semiconductor CrPS4 nanoflakes via the mechanical exfoliation and transfer method. We investigate the detailed temperature and FM thickness dependences of the coercive field HC and the exchange bias field HEB by isothermal anomalous Hall resistance loops with several field cooling processes. Our results indicate that HC increases monotonically with decreasing FM nanoflake thickness t, consistent with the significant enhancement of PMA with the decrease of t in the single Fe5−xGeTe2 nanoflakes. Additionally, we observe a moderate exchange bias effect below the blocking temperature of 20 K, which is significantly below the Néel temperature TN = 38 K of the bulk CrPS4. Unlike HC, HEB shows a saturation or drop tendency as the thickness t is less than 35 nm. Our findings highlight the feasibility of achieving an apparent interfacial magnetic coupling in 2D magnetic vdWs heterostructures via a mechanical exfoliation and transfer approach, which may facilitate the applications of 2D magnetic vdWs in spintronics.