Magnetotransport properties of layered Fe ₃ GeTe ₂ crystals

Abstract Van der Waals layered magnetic materials have recently received significant attention for their ability to exhibit antiferromagnetic or ferromagnetic (FM) properties, even at the few-layer or monolayer scale. Among them, Fe 3 GeTe 2 is one of the most extensively studied systems, crystallizing in a hexagonal structure as an itinerant FM with a Curie temperature ( T C ) of ∼220 K in bulk form and strong magnetic anisotropy. In this study, temperature and magnetic field dependence of the four-probe resistance ( <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" overflow="scroll"> <mml:mrow> <mml:mrow> <mml:msub> <mml:mi>R</mml:mi> <mml:mrow> <mml:mi>x</mml:mi> <mml:mi>x</mml:mi> </mml:mrow> </mml:msub> </mml:mrow> <mml:mo stretchy="false">)</mml:mo> <mml:mo>,</mml:mo> <mml:mrow> <mml:mtext> </mml:mtext> </mml:mrow> </mml:mrow> </mml:math> thermopower (TEP) ( S ), and Hall resistance ( <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" overflow="scroll"> <mml:mrow> <mml:mrow> <mml:msub> <mml:mi>R</mml:mi> <mml:mrow> <mml:mi>x</mml:mi> <mml:mi>y</mml:mi> </mml:mrow> </mml:msub> </mml:mrow> </mml:mrow> </mml:math> ) were investigated in thick Fe 3 GeTe 2 flakes with different thicknesses to understand electron and spin transport, as well as spin and magnetic states. <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" overflow="scroll"> <mml:mrow> <mml:mrow> <mml:msub> <mml:mi>R</mml:mi> <mml:mrow> <mml:mi>x</mml:mi> <mml:mi>x</mml:mi> </mml:mrow> </mml:msub> </mml:mrow> </mml:mrow> </mml:math> decreased with decreasing temperature, confirming metallic behavior, consistent with the observed reduction in the magnitude of the negative TEP. Negative magnetoresistance (MR) with the magnetic field normal to the sample plane exhibited a quadratic field dependence below T C . An anomalous Hall effect was observed below T C , where <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" overflow="scroll"> <mml:mrow> <mml:mrow> <mml:msub> <mml:mi>R</mml:mi> <mml:mrow> <mml:mi>x</mml:mi> <mml:mi>y</mml:mi> </mml:mrow> </mml:msub> </mml:mrow> <mml:mrow> <mml:mo>(</mml:mo> <mml:mrow> <mml:mi>B</mml:mi> <mml:mrow> <mml:mtext> </mml:mtext> </mml:mrow> </mml:mrow> <mml:mo>)</mml:mo> </mml:mrow> </mml:mrow> </mml:math> showed a linear field dependence at low fields and saturation at higher fields. The anomalous Hall resistance ( <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" overflow="scroll"> <mml:mrow> <mml:msubsup> <mml:mi>R</mml:mi> <mml:mrow> <mml:mi>x</mml:mi> <mml:mi>y</mml:mi> </mml:mrow> <mml:mi>A</mml:mi> </mml:msubsup> </mml:mrow> </mml:math> ) followed a dependence of <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" overflow="scroll"> <mml:mrow> <mml:mi>α</mml:mi> <mml:mrow> <mml:msub> <mml:mi>R</mml:mi> <mml:mrow> <mml:mi>x</mml:mi> <mml:mi>x</mml:mi> </mml:mrow> </mml:msub> </mml:mrow> <mml:mo>+</mml:mo> <mml:mi>β</mml:mi> <mml:msubsup> <mml:mi>R</mml:mi> <mml:mrow> <mml:mi>x</mml:mi> <mml:mi>x</mml:mi> </mml:mrow> <mml:mn>2</mml:mn> </mml:msubsup> </mml:mrow> </mml:math> . A positive in-plane MR was observed when the current was perpendicular to the magnetic field, attributed to increased scattering from the enhanced Lorentz force and related orbital effects. Additionally, a hysteresis behavior was observed when cycling the in-plane magnetic field, likely due to the delay in domain alignment in response to the changing field.