Spin glass-like and exchange bias behavior in the van der Waals Fe1/4-<i>δ</i>NbS2 single crystal

Manipulating different magnetic ground states in single-phase compounds is crucial for understanding and achieving a significant exchange bias effect. Here, Fe-vacancy doping into the perfect lattice of two-dimensional antiferromagnet Fe1/4NbS2 is achieved by growing Fe1/4-δNbS2 (δ = 0.01, 0.02, 0.05, and 0.09) single crystals. Coexistence of vacancy-induced ferromagnetic (FM) and antiferromagnetic (AFM) matrix phases is demonstrated in these compounds, with a low-temperature spin glass-like (SG-like) phase further identified. It is established that the magnetic ground state transitioned from strong AFM/weak SG to moderate AFM/SG and eventually to FM/SG with increasing Fe vacancies. Along with this transition, we observe a small exchange bias (EB) in δ = 0.01 and 0.02 (HEB = 0.074 and 0.13 T at 2 K), a giant one in δ = 0.05 (HEB = 1.04 T at 2 K), and a nearly negligible one in δ = 0.09. Our results prove the indispensable role of SG and AFM phases in engendering large EB effect in van der Waals two-dimensional magnets. This study can provide valuable insights into the exchange bias mechanism of two-dimensional bulk materials and offer efficient strategies for achieving substantial exchange bias fields.