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The impact of defects on the performance of spintronic devices has traditionally been viewed as detrimental.
However, this perspective oversimplifies the complex roles that defects can play in enhancing device
functionality. In this talk, the role of defects—whether inherent or deliberately implemented—within the
spacer layer of spintronic nanodevices, and harnessing them for various strategic applications, ranging from
information encoding to energy generation, will be discussed.
The first type of defects that will be discussed are the oxygen vacancies, an inherent structural defect
occurring in the MgO spacer (tunneling) layer of a class of spintronic devices popularly known as magnetic
tunnel junctions (MTJs). Flowing an electrical current that is both of high areal density and large spin
polarization across a MTJ can, through spin-transfer torque (STT), alter the relative magnetic orientation
of the MTJ’s ferromagnetic electrodes. This effect has enabled key next-generation MTJ applications and
commercialized products ranging from radiation immune standalone and embedded non-volatile memories
(STT-MRAMs), microwave radar generation and detection, to artificial neurons for stochastic and brain-
inspired neuromorphic computing. Yet, even as MTJs are now downscaled to 2nm, basic experimental data
challenge the accepted understanding of these spintronic devices operate. We demonstrate that oxygen
vacancies in the MgO tunnel barrier play a crucial role in the STT mechanism. Transport spectroscopy,
ferromagnetic resonance experiments and ab-initio calculations reveal that the high conductivity of STT-
ready MTJs, and the STT effect therein, is mediated by oxygen vacancy complexes within the MgO barrier.
This case study on the ‘simple’ MgO oxide should more broadly inspire the oxide electronics community
as it goes nanoscale to implement the ‘more than Moore’ paradigm.
The talk will then shift to the potential advantages of replacing the inorganic spacer layer (MgO) in existing
MTJs by molecular spacer layer (CoPc), spin-flip excitations in CoPc antiferromagnetic molecular spin
chain, and applications of these spintronic nanodevices for information encoding.
Finally, the second types of defects that will be discussed are the paramagnetic centers (defects arising due
to the magnetic disorder), deliberately implemented in CoPc molecular spacer layer of inorganic-organic
(hybrid) spintronic nanodevices. These deliberately implemented Co paramagnetic centers along with
Fe/C60 spintronic selectors with tunneling assymetry give rise to non-zero spontaneous current flow across
these spintronic nanodevices at room temperature. We reported the record large enduring spontaneous
currents (>90mins), and output power as high as 27nW(450nW) at 300K(40K). Our results leapfrog prior
research and indicate that further developing this technology could help in accelerating the transition to
clean energy.
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References:
1. Kandpal L M Localized States in the Spacer Layer of Spintronic Nanodevices, Doctoral Thesis,
Université de Strasbourg, France (2021)
2. Schleicher F,... Kandpal L M, ........and Bowen M Consolidated Picture of Tunnelling Spintronics
across Oxygen Vacancy States in MgO Journal of Physics D: Applied Physics 52 305302 (2019)
3. Kandpal L M,....... and Bowen M Oxygen Vacancy driven Spin-Transfer Torque across MgO
Magnetic Tunnel Junctions, under review in npj Spintronics-Nature (2024)
4. Katcko K,..... Kandpal L, ... and Bowen M Encoding Information on the Excited State of a Molecular
Spin Chain Advanced Functional Materials 31 2009467 (2021)
5. Chowrira B*, Kandpal L*, .........and Bowen M Quantum Advantage in a Molecular Spintronic
Engine that Harvests Thermal Fluctuation Energy Advanced Materials 34 2206688 (2022),
*contributed equally |