Tunneling Spin Valves Based on Fe₃GeTe₂/hBN/Fe₃GeTe₂ van der Waals Heterostructures

Abstract

Thin van der Waals (vdW) layered magnetic materials hold the possibility of realizing vdW heterostructures with new functionalities. Here, we report on the realization and investigation of tunneling spin valves based on van der Waals heterostructures consisting of an atomically thin hBN layer acting as tunnel barrier and two exfoliated FeGeTe crystals acting as ferromagnetic electrodes. Low-temperature anomalous Hall effect measurements show that thin FeGeTe crystals are metallic ferromagnets with an easy axis perpendicular to the layers and a very sharp magnetization switching at magnetic field values that depends slightly on their geometry. In FeGeTe/hBN/FeGeTe heterostructures, we observe textbook behavior of the tunneling resistance, which is minimum (maximum) when the magnetization in the two electrodes is parallel (antiparallel) to each other. The magnetoresistance is 160% at low temperature, from which we determine the spin polarization of FeGeTe to be 0.66, corresponding to 83% and 17% of the majority and minority carriers, respectively. The measurements also show that, with increasing temperature, the evolution of the spin polarization extracted from the tunneling magnetoresistance is proportional to the temperature dependence of the magnetization extracted from the analysis of the anomalous Hall conductivity. This suggests that the magnetic properties of the surface are representative of those of the bulk, as may be expected for vdW materials.

Ultrathin Scattering Spin Filter and Magnetic Tunnel Junction Implemented by Ferromagnetic 2D van der Waals Material

“…With increasing voltage, TMR gradually decreases to 78% at 1.0 V. We also examine the TMR of two bulks of FGT separated by hBN (Figure S2, Supporting Information), obtaining a TMR of 289% at zero bias voltage (Figure S2e, Supporting Information). It is worth noting that our value is closer to the experimental value31 than ref. 40 Here, the two‐probe model for mesoscopic electronic scattering is closer to the experimental setup, and thus we infer that our simulation could give reliable results in accordance with the actual situation.…”

“…At the parallel state, single‐layer FGT‐hBN‐FGT heterostructure presents a behavior of spin filtering with a polarization of 79% at zero bias (Figure S3, Supporting Information). The TMR of such FGT‐hBN‐FGT heterostructure originates from the ferromagnetism of two thin FGT layers, which is different from the bulk FGT in experiments31 and results in different spin polarization and TMR.…”

Van der Waals magnets: Wonder building blocks for two‐dimensional spintronics?

“…Middle panels: zoom‐in of the magnetoresistance around ±0.7 T. Lower panels: anomalous Hall effect measurements performed on the two Fe 3 GeTe 2 electrodes forming the heterostructure. L1 and L2 represent layer 1 and layer 2 . E, Effective switching current as a function of in‐plane negative and positive bias field.…”

“…A more conventional MTJ architecture is composed of thin insulators sandwiched by two magnetic electrodes, such as Fe 3 GeTe 2 /h‐BN/Fe 3 GeTe 2 . In this structure, the bottom and top Fe 3 GeTe 2 layers are magnetically decoupled by the h‐BN layer, enabling them to switch independently (Figure D).…”

“…111 A more conventional MTJ architecture is composed of thin insulators sandwiched by two magnetic electrodes, such as Fe 3 GeTe 2 /h-BN/Fe 3 GeTe 2 . 109 In this structure, the F I G U R E 6 A, Schematic view of vdW-MTJ based on bilayer CrI 3 . 39 B, Tunneling current verses out-of-plane magnetic field at bias voltage (−290 mV) (upper panel) and the corresponding RMCD signal of device in A (lower panel).…”