UC Berkeley

Transition metal dichalcogenides (TMDs) constitute a class of materials wherein transition metals coordinated by bridging chalcogenides form two-dimensional layers that stack via van der Waals (vdW) interactions along the crystallographic c axis. This lamellar structure enables a diverse range of species, including transition metals, to be intercalated into these vdW interfaces. With open-shell intercalants, local magnetic moments can be introduced into the lattice, thereby inducing long-range magnetic order. The versatility of potential intercalants and host lattices has long made this class of materials an appealing choice as tunable platforms for investigating the interplay among composition, structure, and magnetism. More recently, there has been a growing appreciation for the influence of defects and domain structures in these intercalated compounds on exchange interactions and magnetic correlations. This recognition has led to the acknowledgment of complex magnetic phase spaces, highlighting the intricate interplay between structural features and magnetic properties.We design a spin glass with strong spin frustration induced by magnetic disorder by exploiting the distinctive structure of Fe intercalated ZrSe2, where Fe(II) centers are shown to occupy both octahedral and tetrahedral interstitial sites and to distribute between ZrSe2 layers without long-range structural order. Notably, we observe behavior consistent with a magnetically frustrated and multidegenerate ground state in these FexZrSe2 single crystals, which persists above room temperature. Moreover, this magnetic frustration leads to a robust and tunable exchange bias up to 250 K. These results not only offer important insights into the effects of magnetic disorder and frustration in magnetic materials generally, but also highlight as design strategy the idea that a large exchange bias can arise from an inhomogeneous microscopic environment without discernible long-range magnetic order. In addition, these results show that intercalated TMDs like FexZrSe2 hold potential for spintronic technologies that can achieve room temperature applications. Since Fe intercalated ZrSe2 is semiconducting which provides us a knob to tune its physical and chemical properties electrochemically inserting a foreign species (Li+ ions) into their interlayer spacing. We discover substantial enhancement of light transmission and electrical conductivity in thin (∼30 nm) Fe intercalated ZrSe2 nanosheets after Li intercalation due to changes in band structure and the injection of large amounts of free carriers. We also capture the first in situ optical observations of Li intercalation FexZrSe2, shedding light on the dynamics of the intercalation process. The high reversibility of the intercalation process might be attributed to the enhanced stability of the structure induced by the intercalated Fe ion between the host lattice layers. The enhancement of electron transport upon the Li intercalation in the materials lays down a robust groundwork for electrostatic control over spin polarization. We also briefly explore the effect of semiconducting spin glass FexZrSe2 on generating and manipulating spin current in heavy metal, which highlights the potential application of the materials in spintronic technology. Together, we study the interplay among composition, structure, and magnetism of Fe intercalated ZrSe2, explore the impact of electrostatic and electrochemical strategies to manipulate the properties of FexZrSe2, lay down the robust cornerstone for the application of FexZrSe2 in spintronic technology, and inspire the research interest in expanding the knowledge of the magnetic ion intercalated TMDs to diverse 2D heterostructures and twist moiré patterns.