Thickness- and gate-tunable ferromagnetism in low-dimensional Fe₃GeTe₂ nanoflakes

Abstract

This study investigates thickness- and gate-dependent magnetism in low-dimensional van der Waals ferromagnet Fe₃GeTe₂ nanoflakes. The objective was to quantify how critical magnetic parameters evolve when approaching the two-dimensional limit and under electrostatic carrier modulation. High-quality single crystals were grown by self-flux, and flakes with thicknesses between 7.5 and 26 nm were isolated, encapsulated with hexagonal boron nitride, and fabricated into Hall-bar devices. Magnetotransport, polar magneto-optical Kerr effect, and SQUID magnetometry were employed to probe Curie temperature, coercive field, anisotropy, anomalous Hall conductivity, and interlayer exchange. The results reveal a systematic reduction of Curie temperature from 206 K at 26 nm to 156 K at 7.5 nm, consistent with finite-size scaling. Coercive field increased nearly threefold across the same thickness range, accompanied by high anisotropy fields of 4–6 T, indicating enhanced surface-driven perpendicular magnetic anisotropy. Anomalous Hall conductivity rose with thickness and was dominated by intrinsic Berry curvature contributions. Magneto-optical measurements confirmed weakening of interlayer exchange coupling from 0.12 to 0.06 mJ·m⁻² as thickness decreased, marking the crossover toward quasi-two-dimensional behavior. Electrostatic gating of intermediate-thickness flakes shifted the Curie temperature by approximately 5 K per 10¹³ cm⁻² carrier density and reduced coercivity by about 10%, demonstrating effective electrical control of itinerant ferromagnetism. These findings establish a coherent picture of how thickness and carrier density tune magnetic order in Fe₃GeTe₂ nanoflakes. The results address the central research problem and highlight pathways for exploiting electrically tunable two-dimensional magnets in low-power spintronic applications.