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Low Temperature Deposition of Magnetic Materials on Topological Materials

Description:

TECHNOLOGY AREA(S): Materials 

OBJECTIVE: Develop a technique/approach/methodology to deposit known crystalline ferromagnetic or antiferromagnetic insulators on topological materials such as Bi2Se3 at low temperature below 300~400°C. 

DESCRIPTION: Since Topological insulators (TIs) were discovered a decade ago, the understanding of this new physical phenomena progressed rapidly as evidenced in literature growth. However, the technological potential of this interesting new class of materials has not advanced sufficiently for technology realization. The goal of this topic is to address the traditionally weak link between knowledge generation and applied research/engineering to accelerate the pace of new technology development. Among the known TIs, high quality Bi2Se3 in combination with ferromagnetic (FM) and antiferromagnetic (AFM) materials forming a planar heterojunction is expected to provide a unique opportunity to develop energy efficient electronics ranging from low power switching and memory to energy harvesting. A TI channels electrical current through 100% spin polarized surface states ensuring a very highly efficient exchange interaction with adjacent magnetic materials. The resulting spin orbit torque transfer [1] enables magnetic order in an FM or AFM to be switched at much lower energies than can be achieved with conventional heavy metals. Proposed TI-based energy efficient electronics have, however, been hampered because standard approaches to epitaxy of magnetic materials such as molecular beam epitaxy and pulsed laser deposition require sample temperatures above what TIs can survive. Deposition of the TI on the magnetic material is also ill suited for device and circuit patterning and does not surmount the challenge. Because of the excitement and nascent nature of the field of topological materials, alternative methods for building heterostructures with other materials, ranging from mechanical approaches to low temperature chemical techniques have not yet been considered. Such techniques have been established in other electronic materials but have not been applied in the context of topological plus magnetic materials. This STTR topic therefore seeks an innovative technique/approach/methodology for the deposition of known insulating FM or AFM materials on topological materials such as Bi2Se3 (other well investigated TI materials with spin polarized topologically protected electronic surface states are also of interest) at low temperature (e.g. below 300°C) so that the integrity of the underlying TI material is maintained by its own chemical and physical stability. Key aspects to form the heterostructure are (i) the control of the formation of the terminating top atomic layer on the surface of TI materials, (ii) the formation of the first atomic layers of the deposited magnetic material on the TI material, and (iii) sustaining the magnetic order of the magnetic material. Layer by layer deposition preserving the underlying TI quality is highly desired under a set of available parameters such as temperature, pressure, deposited thickness and speed. The created interface/heterostructure, as demonstrated in Ref [1-2], is expected to be characterized by advanced measurement and analysis to determine the interface structure and the electronic and magnetic interactions between the two different materials. Understanding the relationship of the interface characteristics as well as the nature and extent of the electronic/magnetic interactions is expected for iterated tunings and optimizations. Alternative techniques to create structurally well-defined and atomically regular interfaces between magnetic materials (as an over-layer) and high quality TI materials (as a substrate) will be considered. 

PHASE I: Demonstrate low temperature deposition or alternative method for interfacing magnetic materials on dichalcogenide topological insulators. Theoretical and computational efforts may also be included. The results of Phase I should demonstrate a path forward toward optimized materials, interfaces and control over the interface exchange interaction. 

PHASE II: Demonstrate low temperature juxtaposition (deposition or other technique) of high quality magnetic insulators on high quality topological insulators. The “high quality” metric is defined by a heterostructure that retains the performance characteristics of the topological insulator and is suitable for control of the magnetic anisotropy or antiferromagnetic Neél order driven by electrical current through the topological insulator. Magnetic, electronic, structural and chemical characterization of the topological insulator(s) and magnetic insulator(s) post-interfacing is required. Structural and chemical analysis of the interface itself must be included. Analysis of the exchange interaction at the interface itself would be ideal. Delivery of samples is expected for government qualification of the resulting heterostructures. 

PHASE III: If sufficiently high quality heterostructures and interfaces are formed, this effort should further optimize the technique and include topological-magnetic device design and fabrication for energy efficient electronic devices in application areas such as THz detection, switching or energy harvesting. 

REFERENCES: 

1: A. R. Mellnik, J. S. Lee, A. Richardella, J.L.Grab, P. J. Mintun, M. H. Fischer, A.Vaezi, A.Manchon, E.-A.Kim, N. Samarth and D. C. Ralph "Spin-transfer torque generated by a topological insulator" Nature, 511, 449 (2014)

2:  doi:10.1038/nature13534.

3:  Y. G. Semenov, X. Duan and K. W. Kim, "Voltage-driven magnetic bifurcations in nanomagnet-topological insulator heterostructures" Phys. Rev. B 89, 201405(R) (2014)

4:  doi: 10.1103/PhysRevB.89.201405.

5:  Y. G. Semenov, X.-L. Li, and K. W. Kim, "Currentless reversal of Néel vector in antiferromagnets" Phys. Rev. B 95, 014434 (2014)

6:  doi:10.1103/PhysRevB.95.014434

KEYWORDS: Topological Insulator, Magnetic, Epitaxy, Deposition, Heterostructure, Interface, Energy Efficient Electronics, Manufacturing Process, Manufacturing Materials 

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