One of the main tasks in the investigation of 2-dimensional transition metal dichalcogenides is the determination of valley lifetimes. In this work, we combine time-resolved Kerr rotation with electrical transport measurements to explore the gate-dependent valley lifetimes of free conduction band electrons of monolayer WSe2. When tuning the Fermi energy into the conduction band we observe a strong decrease of the respective valley lifetimes which is consistent with both spin-orbit and electron-phonon scattering. We explain the formation of a valley polarization by the scattering of optically excited valley polarized bright trions into dark states by intervalley scattering. Furthermore, we show that the conventional time-resolved Kerr rotation measurement scheme has to be modified to account for photo-induced gate screening effects. Disregarding this adaptation can lead to erroneous conclusions drawn from gate-dependent optical measurements and can completely mask the true gatedependent valley dynamics.
Rare earth iron garnets (REIG’s) are important component materials in magnetic insulator based spintronics due to their low spin wave damping and electrically insulating properties. Yttrium iron garnet (YIG) has been the mainstay material because of its unusually low spin damping. However, YIG thin films thus far have in-plane magnetization. Recent studies on thulium iron garnet (TIG) thin films have demonstrated robust perpendicular magnetic anisotropy (PMA), however, spin damping in TIG films is significantly higher compared to YIG. It would be useful to have an insulating magnetic material that exhibits both low spin damping and robust, tunable PMA because of its potential for novel device configurations. In this study, we synthesized YIG-TIG solid solution powders across the compositional phase diagram and with different particle sizes using the polymeric steric entrapment technique in order to begin to decouple compositional effects from size and morphological effects. Powder characterization, including XRD, VSM, SEM and FMR techniques, was also performed to understand their magnetic behavior.
Ultrafast control of magnetic order in materials requires a fundamental understanding of how energy and angular momentum flow between electronic, magnetic, and vibrational degrees-of-freedom. We investigate the ultrafast response of Au/TmIG and Au/YIG bilayers to ultrafast laser heating of the Au electrons. In the picoseconds after heating, large interfacial spin currents occur due to a temperature imbalance between electrons and phonons in the metal, and magnons and phonons in the magnetic insulator. We utilize four different optical probes to develop a complete picture of the heat and spin transport in Au/TmIG and Au/YIG. Magneto-optic Kerr effect measurements of Au at a wavelength of 800 nm detects the spin accumulation in the normal metal that results from interfacial spin-currents. Magneto-optic Kerr effect measurements at 400 nm monitor the ultrafast magnetization dynamics of the garnet insulator that occur due to increases in magnon population. Finally, thermoreflectance measurements at 690 and 950 nm monitor the temperature evolution of the Au electrons and phonons, respectively. Together, these measurements allow us to estimate the magnitude of the transport coefficients responsible for the longitudinal spin-Seebeck effect in these systems. These coefficients include the electron-magnon conductance of the Au/TmIG and Au/YIG interfaces, the electron-phonon coupling in the Au layer, and the magnon-phonon coupling in the TmIG and YIG layers.
This paper presents a novel design concept for spintronic nanoelectronics that emphasizes a seamless integration
of spin-based memory and logic circuits. The building blocks are magneto-logic gates based on a hybrid
graphene/ferromagnet material system. We use network search engines as a technology demonstration vehicle
and present a spin-based circuit design with smaller area, faster speed, and lower energy consumption than the
state-of-the-art CMOS counterparts. This design can also be applied in applications such as data compression,
coding and image recognition. In the proposed scheme, over 100 spin-based logic operations are carried
out before any need for a spin-charge conversion. Consequently, supporting CMOS electronics requires little
power consumption. The spintronic-CMOS integrated system can be implemented on a single 3-D chip. These
nonvolatile logic circuits hold potential for a paradigm shift in computing applications.
Spin transport in graphene devices has been investigated in both local and non-local spin valve geometries. In the nonlocal
measurement, spin transport and spin precession in single layer and bilayer graphene have both been achieved with
transparent Co contacts. Gate controllable non-local spin signal was also demonstrated in this system. For the local
graphite spin valve device, we report MR up to 12% for devices with tunneling contacts. We observe a correlation
between the nonlinearity of the I-V curve and the presence of local MR and conclude that tunnel barriers can be
employed to surmount the conductance mismatch problem in this system. These studies indicate that the improvement of
tunnel barriers on graphene, especially to inhibit the formation of pinholes, is an important step to achieve more efficient
spin injection into graphene.
Conference Committee Involvement (17)
Spintronics XVIII
3 August 2025 | San Diego, California, United States
Spintronics XVII
18 August 2024 | San Diego, California, United States
Spintronics XVI
20 August 2023 | San Diego, California, United States
Spintronics XV
21 August 2022 | San Diego, California, United States
Spintronics XIV
1 August 2021 | San Diego, California, United States
Spintronics XIII
24 August 2020 | Online Only, California, United States
Spintronics XII
11 August 2019 | San Diego, California, United States
Spintronics XI
19 August 2018 | San Diego, California, United States
Spintronics X
6 August 2017 | San Diego, California, United States
Spintronics IX
28 August 2016 | San Diego, California, United States
Spintronics VIII
9 August 2015 | San Diego, California, United States
Spintronics VII
17 August 2014 | San Diego, California, United States
Spintronics VI
25 August 2013 | San Diego, California, United States
Spintronics V
12 August 2012 | San Diego, California, United States
Spintronics IV
21 August 2011 | San Diego, California, United States
Spintronics III
1 August 2010 | San Diego, California, United States
Spintronics II
2 August 2009 | San Diego, California, United States
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