APS March Meeting Poster Presentation.

1. Interface and spintronic device characteristics of layered insulators
(BN, Bi2Se3) grown in amorphous form using magnetron sputtering
Yub Raj Sapkota, Duston Wetzel, and Dipanjan Mazumdar, Department of Physics, Southern Illinois University Carbondale, IL, 62901
Abstract: The last two decades have witnessed the emergence of several layered insulators such as hexagonal Boron nitride (BN) and Topological Insulator Bismuth selenide (Bi2Se3).
Their application in spintronics is still an active area of research. In this work, we have investigated the interface, transport, and magnetotransport properties of amorphous BN and
Bi2Se3 in a tunnel magnetoresistance geometry with ferromagnetic Cobalt layers. We observed tunneling and magnetoresistance behavior with BN barriers, whereas interdiffusion issues
likely impeded the observation of magnetoresistance effect with insulating Bi2Se3.
• Sputtered Bi2Se3/FM bilayers showed giant Spin–Orbit
Torque[1], and Tunnel magnetoresistance effect with Bi2Se3
insulating layer is predicted theoretically to exceed 1000%[2].
Some tunnel magnetoresistance devices is also reported with
CVD grown h-BN [3].
• We have previously demonstrated that the properties of Bi2Se3
can be tailored as a function of thickness, particularly below 6
quintuple layers, which is very suitable for spintronics
applications [4,5].
• We present a detailed interface study and preliminary magneto-
transport properties of Co-Bi2Se3-Co and Co-BN-Co pseudo
spin-valves in a tunnel magnetoresistance geometry. All layers
are grown in amorphous form using magnetron sputtering.
1) DC Mahendra, R. Grassi, JY Chen, M. Jamal, J-P Wang, Nature
Materials 17 800 (2018)
2) M. Gotte , T Paananen, G. Reiss, T. Dahm Phys. Rev. App. 2
054010 (2014)
3) M. Piquemal-Banci, et. al. Appl. Phys. Lett 108 102404 (2016)
4) Y R. Sapkota, and D Mazumdar, J. Appl. Phys. 120 105306 (2018)
5) Y.R Sapkota, A . Alkabsh, A. Walber, H. Samassekou and D.
Mazumdar, Appl. Phys. Lett. 110 181901 (2017)
• X-ray reflectivity data on trilayer Co-Bi2Se3-Co was difficult to model, possibly due to large
interdiffusion at both the bottom and top interfaces (fig. c).
• Linear IV curve observed on Bismuth selenide-based TMR device, indicating metallic behavior.
This is possibly due to large interdiffusion as inferred from the x-ray reflectivity data.
• Non-linear current-voltage characteristics was obtained on Co-BN-Co micropillars consistent
with tunneling behavior (fig. d).
• Preliminary MR results on Co-BN-Co also indicated evidence of tunnel magnetoresistance effect
at room temperature (inset of fig. d). Values between 1-10% was obtained on different devices.
Introduction
(a) (b)
Introduction
References
Interface and device properties of amorphous Bi2Se3 and BN with Cobalt
Conclusion
Experimental
• High purity Bismuth selenide and Boron nitride targets were
sputtered under r.f. conditions and Cobalt under dc conditions in
a high vacuum sputtering chamber (< 10-8 Torr).
• All layers were grown at room temperature to inhibit diffusion.
• 500 mm circular micropillar devices were defined during growth
using shadow mask technique.
• Transport and magnetoresistance (MR) measurements were
performed using two-probe method in a custom-made probe
station at room temperature.
Co/Bi2Se3
Co/BN/Co
Co/Bi2Se3/Co Co/Bi2Se3/Co
Co/BN/Co
XRR of Co-Bi2Se3 bilayer
• We were able to obtain a reasonable fit to
the x-ray reflectivity data on Co/Bi2Se3
bilayer only after introducing an extra
interfacial layer.
• Our analysis reveal a 1 nm interfacial
layer in Co/Bi2Se3 as shown in Figure (a).
Such an interfacial layer is surprising
since the layers were deposited at room
temperature to minimize diffusion.
• Average roughness of each layer was also
high that will likely lead to significant
spin-scattering.
XRR of Co-BN-Co trilayer
Reasonable fit to trilayer Co-BN-Co was
obtained without the addition of any extra
interfacial layer as shown in fig (b). This
indicates that diffusion is minimal with
relatively sharper interfaces compared to
Co/Bi2Se3.
(c) (d)
• BN tunnel barriers show sharp interfaces
with ferromagnetic Cobalt, whereas an
interfacial layer is detected at the interface
of Bi2Se3 and Co.
• Robust tunneling IV behavior leading to
Tunnel MR is observed with BN barriers
whereas Bi2Se3 shows metallic transport
characteristics.
• Interdiffusion issues with Bi2Se3 and Co is
likely detrimental for spintronics
applications.
This work is supported by NSF CAREER grant (ECCS: Award#1846829)