Kacho Imtiyaz Ali Khan

Van der Waals (vdW) heterostructures combining two‐dimensional (2D) ferromagnets and semiconducting transition‐metal dichalcogenides (TMDCs) offer highly promising opportunities for tailoring 2D magnetism through interfacial proximity effects, enabling unique physical phenomena inaccessible in 3D systems and achieving functionalities beyond conventional spintronics. However, current fabrication of vdW heterostructures still relies heavily on the manual stacking of exfoliated 2D flakes, leading to critical challenges in scalability, interfacial quality, thickness control and device integration. This work reports on the realization of all‐epitaxial, high‐quality Fe _{5− x} GeTe ₂ (FGT)/WSe ₂ heterostructures exhibiting perpendicular magnetic anisotropy (PMA) and room‐temperature ferromagnetism. The FGT/WSe ₂ system demonstrates temperature‐driven magnetic transitions, higher‐order PMA contributions and large anisotropic magnetoresistance, highlighting sublattice‐specific contributions to magnetic and transport properties. Notably, the FGT/WSe ₂ heterostructures display unconventional physical phenomena, including thickness‐ and temperature‐dependent sign reversal of exchange bias, a reversed thickness trend in the unconventional Hall effect, and a non‐monotonic PMA‐thickness dependence. These anomalies indicate pronounced interfacial contributions arising from proximity effects enhanced by epitaxial interface quality. Collectively, this study provides deep insights into the magnetic and transport properties of FGT/WSe ₂ vdW heterostructures, establishing a scalable platform for exploring emergent 2D physics and developing next‐generation 2D spintronic functionalities.

Fe₃GaTe₂ (FGaT), a two-dimensional (2D) layered ferromagnetic metal, exhibits a high Curie temperature (T_C) of ∼360 K along with strong perpendicular magnetic anisotropy (PMA), making it a promising material candidate for next-generation energy-efficient magnetic devices. However, the vast majority of studies on FGaT to date have been limited to millimeter-sized bulk crystals and exfoliated flakes, which are unsuitable for practical applications and integration into device processing. Also, its combination with other 2D materials to form van der Waals (vdW) heterostructures has only been achieved by flake stacking. Consequently, the controlled large-area growth of FGaT and related heterostructures remains largely unexplored. In this work, we demonstrate the high-quality, large-area growth of epitaxial FGaT thin films on single-crystalline graphene/SiC templates using molecular beam epitaxy. Structural characterization confirms the high crystalline quality of the continuous FGaT/graphene vdW heterostructures. Temperature-dependent magnetization and anomalous Hall measurements reveal robust PMA with an enhanced T_C well above room temperature, reaching up to 400 K. Furthermore, X-ray absorption and X-ray magnetic circular dichroism spectra provide insight into the spin and orbital magnetic moment contributions, further validating the high T_C and robust PMA. These findings are highly significant for the future development of high-performance spintronic devices based on 2D heterostructures, with potential applications in next-generation data storage, logic processing, and quantum technologies.

Angle‐resolved spin‐torque ferromagnetic resonance measurements are carried out in heterostructures consisting of Py (Ni ₈₁ Fe ₁₉ ) and a noncollinear antiferromagnetic quantum material IrMn ₃ . The structural characterization reveals that IrMn ₃ is polycrystalline in nature. A large exchange bias of 158 Oe is found in Py/IrMn ₃ at room temperature, while IrMn ₃ /Py and Py/Cu/IrMn ₃ exhibit no exchange bias. Regardless of the exchange bias and stacking sequence, a substantial unconventional out‐of‐plane anti‐damping torque is observed when IrMn ₃ is in direct contact with Py. The magnitude of the out‐of‐plane spin‐orbit torque efficiency is found to be twice as large as the in‐plane spin‐orbit torque efficiency. The unconventional spin‐orbit torque vanishes when a Cu spacer is introduced between Py and IrMn ₃ , indicating that the unconventional spin‐orbit torque in this system originates at the interface. These findings are important for realizing efficient antiferromagnet‐based spintronic devices via interfacial engineering.

Ultrafast generation of spin currents involving antiferromagnets is currently attracting tremendous interest. Here, we demonstrate broadband THz emission from a [111]-oriented NiO/Pt bilayer grown on MgO and Al₂O₃ substrates. The NiO films are grown by pulsed laser deposition, whereas the Pt films are grown by magnetron sputtering. While we obtained epitaxial films on both substrates, NiO films on the Al₂O₃ substrate showed the presence of crystalline twins. We show that the existence of crystalline twins reduces the THz amplitude by an order of magnitude while simultaneously dramatically changing the azimuthal dependency of the THz amplitude. The findings have significant implications for antiferromagnetic spintronics.

Mn ₃ Sn is a non‐collinear antiferromagnetic quantum material that exhibits a magnetic Weyl semimetallic state and has great potential for efficient memory devices. High‐quality epitaxial c ‐plane Mn ₃ Sn thin films have been grown on a sapphire substrate using a Ru seed layer. Using spin pumping induced inverse spin Hall effect measurements on c ‐plane epitaxial Mn ₃ Sn/Ni ₈₀ Fe ₂₀ , spin‐diffusion length (), and spin Hall conductivity (σ _SH ) of Mn ₃ Sn thin films are measured: nm and cm ⁻¹ . While is consistent with earlier studies, σ _SH is an order of magnitude higher and of the opposite sign. The behavior is explained on the basis of excess Mn, which shifts the Fermi level in these films, leading to the observed behavior. These findings demonstrate a technique for engineering σ _SH of Mn ₃ Sn films by employing Mn composition for functional spintronic devices.

Schematic of kagome Fe₃Sn lattice and anomalous Hall resistivity (ρAHExy) vs. temperature (T) for the Pt and Ta seed layered Fe₃Sn₂ thin films.