Since the discovery of graphene, two-dimensional (2D) materials have become a major research platform for exploring novel quantum phenomena and emerging device functionalities. While early studies focused on atomically thin crystals exfoliated from layered van der Waals (vdW) materials, recent research has increasingly emphasized artificial vdW heterostructures, where interlayer stacking and moiré superlattices provide powerful routes to engineering electronic states. These advances have established structural engineering as a central concept in the design of quantum materials.

In this talk, I will introduce an alternative strategy that exploits another unique structural degree of freedom inherent to layered materials: the van der Waals gap. By introducing and controlling ions within this gap, it becomes possible to tailor electronic structures and magnetic states beyond what can be achieved through stacking engineering alone. Intercalation has long been recognized as an effective means of modifying layered transition-metal dichalcogenides, while electrochemical ion gating offers a reversible and continuous approach for tuning carrier density and correlated electronic states. Together, these techniques provide a versatile platform for investigating and controlling magnetism in layered materials.

Our group has recently developed molecular beam epitaxy (MBE) techniques for the layer-by-layer growth of intercalated van der Waals materials, enabling precise control over crystal structure and intercalant concentration. Combined with post-growth thermal annealing under ultrahigh vacuum and electrochemical Li-ion gating, these epitaxial materials provide an ideal platform for systematically exploring gate-controlled magnetic phenomena.

The presentation will highlight two representative classes of layered magnetic van der Waals materials with distinct electronic structures. In one class, electrochemical ion gating is employed to tune carrier density in systems hosting semimetallic bands near the Fermi level, providing insight into the role of itinerant carriers in stabilizing ferromagnetism. In the other, ion gating is applied to magnetic materials exhibiting flat electronic bands, where carrier modulation offers a unique opportunity to investigate the interplay between electronic correlations and antiferromagnetic order. These studies demonstrate how electrochemical control of carrier density serves as a powerful tool for uncovering the microscopic mechanisms governing magnetism in layered van der Waals materials with diverse electronic structures.

By highlighting recent progress in epitaxial growth, ion engineering, and electrochemical control, this talk will illustrate how the van der Waals gap can serve as a new design space for quantum materials. The ability to manipulate ionic configurations and carrier density in a controlled and reversible manner opens promising opportunities for realizing emergent magnetic phases and developing next-generation spintronic functionalities.