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Giant Tunneling Magnetoresistance in Spin-Filter van der Waals Heterostructures (1801.08679v1)

Published 26 Jan 2018 in cond-mat.mes-hall

Abstract: Magnetic multilayer devices that exploit magnetoresistance are the backbone of magnetic sensing and data storage technologies. Here we report novel multiple-spin-filter magnetic tunnel junctions (sf-MTJs) based on van der Waals (vdW) heterostructures in which atomically thin chromium triiodide (CrI3) acts as a spin-filter tunnel barrier sandwiched between graphene contacts. We demonstrate tunneling magnetoresistance which is drastically enhanced with increasing CrI3 layer thickness, reaching a record 19,000% for magnetic multilayer structures using four-layer sf-MTJs at low temperatures. These devices also show multiple resistance states as a function of magnetic field, suggesting the potential for multi-bit functionalities using an individual vdW sf-MTJ. Using magnetic circular dichroism measurements, we attribute these effects to the intrinsic layer-by-layer antiferromagnetic ordering of the atomically thin CrI3. Our work reveals the possibility to push magnetic information storage to the atomically thin limit, and highlights CrI3 as a superlative magnetic tunnel barrier for vdW heterostructure spintronic devices.

Citations (936)

Summary

  • The paper demonstrates that increasing CrI₃ layers in vdW heterostructures boosts the spin-filter TMR up to 19,000% in four-layer devices.
  • The paper employs intrinsic antiferromagnetic ordering and a double spin-filter effect to correlate tunneling currents with magnetic states in bilayer and trilayer configurations.
  • The paper highlights that controlled magnetic configurations in 2D heterostructures can enable multi-level memory devices, advancing spintronics applications.

Giant Tunneling Magnetoresistance in Spin-Filter van der Waals Heterostructures

This paper presents an exploration into spintronics and magnetoresistance by investigating spin-filter magnetic tunnel junctions (sf-MTJs) formulated from van der Waals (vdW) heterostructures. Utilizing atomically thin chromium triiodide (CrI₃) layered with graphene contacts, the authors demonstrate a significant enhancement in tunneling magnetoresistance (TMR). They reveal that increasing the thickness of CrI₃ layers results in TMR reaching an unprecedented 19,000% in four-layer structures at low temperatures.

The research capitalizes on the intrinsic antiferromagnetic ordering present in CrI₃, wherein each layer aligns antiferromagnetically with its neighbor, contributing to the spin-filter effect. This layer-specific antiferromagnetic property obviates the need for separate spin filters and spacers and facilitates the realization of sharp atomic interfaces crucial for large spin-filter TMR (sf-TMR). The authors argue that as the number of CrI₃ layers increases, so does the sf-TMR, due to a series of aligned spin-filters acting in opposition across the tunnel junctions. This layered structure also allows for multiple magnetic resistance states, hinting at possibilities such as multi-bit functionalities, which could be groundbreaking for spintronics applications like MRAM technology.

For bilayer devices, the tunneling current and the reflective magnetic circular dichroism (RMCD) results corroborate the origin of the giant sf-TMR through a double spin-filtering effect when in antiferromagnetic alignment. It is shown that magnetic currents within bilayers exhibit a strong dependence on the external field, with peaks in sf-TMR of 530% and 310% for in-plane and out-of-plane configurations, respectively. For trilayer and four-layer devices, the sf-TMR magnitudes are greatly amplified to 3,200% and 19,000%, respectively, evidencing the multilayer approach’s efficacy.

The results also indicate an energy-dependent response in the current, attributable to anisotropic spin-orbit coupling and asymmetric interfaces of the device, possibly influenced by layer thickness variations in graphene contacts. The nuanced magnetic configuration of four-layer devices yields several resistance states, suggesting complex underlying magnetic arrangements. These observations suggest the potential to develop multi-level memory devices using vdW heterostructures. However, practical application may be limited presently by the temperature constraints, as these devices are commanded by phenomena that occur near cryogenic conditions.

In conclusion, this research paves the way for the exploration of 2D magnetic materials in spintronic applications with unprecedented performance. Future efforts could focus on maintaining competitive levels of sf-TMR at elevated temperatures for real-world applications and exploring methods for electrical switching between magnetic states. The advancement towards practical desensitization to external fields, alongside an exploration into precise control over complex magnetic states, could immensely benefit the landscape of data storage and magnetic sensing technologies.