Magnetic Proximity Effect as a Pathway to Spintronic Applications of Topological Insulators

Abstract: Spin-based electronics in topological insulators (TIs) is favored by the long spin coherence1,2 and consequently fault-tolerant information storage. Magnetically doped TIs are ferromagnetic up to 13 K,3 well below any practical operating condition. Here we demonstrate that the long range ferromagnetism at ambient temperature can be induced in Bi2-xMnxTe3 by the magnetic proximity effect through deposited Fe overlayer. This result opens a new path to interface-controlled ferromagnetism in TI-based spintronic devices.

Magnetic Proximity Effect in Topological Insulators and Its Implications for Spintronics

This paper investigates the potential for utilizing the magnetic proximity effect to induce room temperature ferromagnetism in topological insulators (TIs), specifically focusing on Bi_2-xMn_xTe₃ through the deposition of an Fe overlayer. The study expands on the capabilities of TIs in spintronic applications, addressing significant challenges related to their magnetic and conducting properties. By leveraging the unique properties of TIs and combining them with magnetic materials, the research provides insights into the possibilities of creating functional and controllable interfaces for future devices.

Key Findings

1. Interface-Controlled Ferromagnetism: The authors demonstrate that the deposition of a thin iron (Fe) overlayer on Mn-doped Bi_2-xMn_xTe₃ induces long-range ferromagnetism at ambient temperature. The induced ferromagnetism at the interface is suggested as a viable method for overcoming the limit of low Curie temperatures often associated with such materials for practical application.

2. Preservation of Topological Properties: Through the use of angle-resolved photoemission spectroscopy (ARPES), the study observes that the deposition of Fe not only induces magnetization but also preserves and emphasizes the topological surface states. This preservation is crucial as it implies that electronic properties vital for spintronic devices are retained even when magnetic materials are introduced.

3. Antiparallel Magnetic Coupling: X-ray Magnetic Circular Dichroism (XMCD) analysis reveals antiparallel alignment of Mn and Fe magnetizations. The interface supports long-range magnetization aligned in the surface plane, confirming that surface magnetization is distinct from the bulk magnetization observed below the intrinsic Curie temperature (T_C) of the TI.

4. Non-Alloying Behavior: The study explicitly confirms the non-alloying behavior of the Fe layer with the Mn-doped substrate. The distinct and separate magnetic signatures of Mn and Fe are evidence against any significant atomic intermixing, allowing both to maintain their unique magnetic properties.

Implications

The findings of this research offer significant theoretical and practical implications for the field of spintronics:

• Design of Spintronic Devices: The ability to induce and control room temperature ferromagnetism at TI interfaces broadens the operational scope for spintronic devices. The manipulation of topological surface states via magnetic proximity introduces a novel method for device engineering, potentially leading to innovative design frameworks for stable and efficient spin-based information processing systems.

• Enhanced Material Understanding: The clarification of interactions at FM/TI interfaces and the implications for surface versus bulk properties provide a deeper understanding of these complex materials. This knowledge facilitates targeted development in material science, particularly in applications where topological durability against magnetic perturbations is necessary.

• Future Research Directions: The paper posits that further exploration of the properties of topological surface states with both magnetic and non-magnetic overlays will be paramount. Investigating how band filling and structural modifications affect these interactions could unveil new phenomena that enhance the utility of TIs in technological applications.

Overall, the study paves the path for continued exploration in topological materials, particularly focusing on their integration into existing technological frameworks via strategic layering with magnetic substances. This research forms a cornerstone for advancing the application potential of TIs within the burgeoning arena of spintronics.