  Superconductor-ferromagnet (S-F) interfaces in two-dimensional (2D)
heterostructures present a unique opportunity to study the interplay between
superconductivity and ferromagnetism. The realization of such nanoscale
heterostructures in van der Waals (vdW) crystals remains largely unexplored due
to the challenge of making an atomically-sharp interface from their layered
structures. Here, we build a vdW ferromagnetic Josephson junction (JJ) by
inserting a few-layer ferromagnetic insulator Cr2Ge2Te6 into two layers of
superconductor NbSe2. Owing to the remanent magnetic moment of the barrier, the
critical current and the corresponding junction resistance exhibit a hysteretic
and oscillatory behavior against in-plane magnetic fields, manifesting itself
as a strong Josephson coupling state. Through the control of this hysteresis,
we can effectively trace the magnetic properties of atomic Cr2Ge2Te6 in
response to the external magnetic field. Also, we observe a central minimum of
critical current in some thick JJ devices, evidencing the coexistence of 0 and
{\pi} phase coupling in the junction region. Our study paves the way to
exploring the sensitive probes of weak magnetism and multifunctional building
blocks for phase-related superconducting circuits with the use of vdW
heterostructures.
