Topological Antiferromagnetic Van der Waals Phase in Topological Insulator/Ferromagnet Heterostructures Synthesized by a CMOS‐Compatible Sputtering Technique

Abstract

Breaking time‐reversal symmetry by introducing magnetic order, thereby opening a gap in the topological surface state bands, is essential for realizing useful topological properties such as the quantum anomalous Hall and axion insulator states. In this work, a novel topological antiferromagnetic (AFM) phase is created at the interface of a sputtered, c‐axis‐oriented, topological insulator/ferromagnet heterostructure—Bi2Te3/Ni80Fe20 because of diffusion of Ni in Bi2Te3 (Ni‐Bi2Te3). The AFM property of the Ni‐Bi2Te3 interfacial layer is established by observation of spontaneous exchange bias in the magnetic hysteresis loop and compensated moments in the depth profile of the magnetization using polarized neutron reflectometry. Analysis of the structural and chemical properties of the Ni‐Bi2Te3 layer is carried out using selected‐area electron diffraction, electron energy loss spectroscopy, and X‐ray photoelectron spectroscopy. These studies, in parallel with first‐principles calculations, indicate a solid‐state chemical reaction that leads to the formation of Ni−Te bonds and the presence of topological antiferromagnetic (AFM) compound NiBi2Te4 in the Ni‐Bi2Te3 interface layer. The Neél temperature of the Ni‐Bi2Te3 layer is ≈63 K, which is higher than that of typical magnetic topological insulators (MTIs). The presented results provide a pathway toward industrial complementary metal−oxide−semiconductor (CMOS)‐process‐compatible sputtered‐MTI heterostructures, leading to novel materials for topological quantum devices.

Effects of Crystalline Disorder on Interfacial and Magnetic Properties of Sputtered Topological Insulator/Ferromagnet Heterostructures

“…(f) XRR plots and theoretical fitting for GBT, DBT, and CBT samples used for characterization of thickness and surface roughness. The data for CBT samples are similar to the ones in ref .…”

“…However, with significantly reduced crystallinity, surprisingly the granular Bi 2 Te 3 samples had a comparable enhanced spin-Hall conductivity as samples with the higher c- axis-oriented Bi 2 Te 3 . This can be attributed to the quantum confinement effect in smaller crystallite grains in granular TI. , Low-temperature m ( H ) and m ( T ) measurements revealed an AFM ordered phase in the predominantly Ni-diffused Bi 2 Te 3 interface from the formation of the topological AFM compound NiBi 2 Te 4 . Interestingly, the strength of the exchange interaction of the interfacial AFM phase, as monitored by the exchange bias, was found to weaken significantly with the increase in disorder of the Bi 2 Te 3 layer.…”

“…TIs possess large spin–orbit coupling (SOC) resulting in dissipation-less surface conducting statestopological surface states (TSS). − Introducing magnetic order in TIs leads to gap opening in the TSS bands and the possibility of dissipation-less quantum anomalous Hall (QAH) and axion insulator states. − Stimulated by these remarkable material properties, TIs are regarded as promising candidates for realization of energy efficient spintronic devices. TIs possess highly reactive surfaces, thus making them susceptible to the formation of interfacial phases when coupled with metallic films. − Because of their composition, these interfacial layers have the potential for hosting topologically nontrivial magnetic phases . The majority of the reported experiments have studied TIs grown from molecular beam epitaxy (MBE), − which is a standard technique for growing high-quality, crystalline-ordered thin films.…”

“…Magnetron sputtering, on the other hand, is the semiconductor industry’s accepted thin film deposition technique because of its potential for high throughput and large area film growth. Sputtering also allows easy deposition of TIs with varying crystalline disorder. − This opens up the possibility of exploration of their disorder-dependent electronic and magnetic properties.…”

“…Recently, the topological antiferromagnetic (AFM) compound NiBi 2 Te 4 was observed in the interface of highly c -axis-oriented sputtered Bi 2 Te 3 /Ni 80 Fe 20 heterostructures . Ni from the Ni 80 Fe 20 (Py) layer diffuses and reacts with Bi 2 Te 3 , and the reaction is promoted by the delocalized TSS electrons. − In addition, recent experiments have shown the presence of Dirac-like surface states even in amorphous Bi 2 Se 3 . In this work, the effects of crystalline structural disorder on the interface and magnetic properties of Bi 2 Te 3 /Py heterostructures are investigated.…”