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Effcective Mass of Dilute Two-Dimensional Holes in a GaAs Heterostructure
Hwayong Noh 한국물리학회 2005 THE JOURNAL OF THE KOREAN PHYSICAL SOCIETY Vol.47 No.1
The eective mass of two-dimensional holes in GaAs has been measured in the dilute regime, where the system exhibits an apparent metal-insulator transition. The mass, determined from the temperature dependence of the Shubnikov-de Haas oscillation amplitudes, shows a strong depen-dence on density, decreasing from 0:8me to 0:4me as the hole density changes from 3 £ 1010 cm¡2 to 1:3 £ 1010 cm¡2. From the measurements under a strong in-plane magnetic ¯eld, it is found that the strong density dependence is related to the triplet interaction corrections.
Pradeep Raj Sharma,Tae Wan Kim,Hwayong Noh 한국자기학회 2021 한국자기학회 학술연구발표회 논문개요집 Vol.31 No.2
Two-dimensional (2D) van der Waals (vdW) ferromagnetic materials have emerged as promising candidates and are recently providing a huge platform for the study of spin-related phenomena and their potential applications. Here we report the thickness and temperature-dependent anomalous Hall and anomalous Nernst effect in h-BN/FGT/SiO₂ van der Waals heterostructures. Interestingly, we have observed the polarity reversal of AHE in a thin flakes of FGT ~15 nm. The anomalous Hall and Nernst effects in a few-layer FGT flake show single domain magnetic structure with nearly square-shaped hall signals and large coercivity, indicating strong perpendicular magnetic anisotropy (PMA). On the other hand, thick (bulk) FGT shows gradual switching with the magnetic field evolution, indicating the presence of multi-domain structures and demonstrate weak PMA. The variation of Curie temperature (TC) and HC with a flake thickness are also presented.
Gautam, Praveen,Sharma, Pradeep Raj,Kim, Y.K.,Kim, T.W.,Noh, Hwayong North-Holland Pub. Co 2018 Journal of magnetism and magnetic materials Vol.446 No.-
<P><B>Abstract</B></P> <P>We report experiments on the temperature dependence of anomalous Hall and anomalous Nernst effects in amorphous [CoSiB/Pt] multilayer films with perpendicular magnetic anisotropy down to low temperatures. The Hall resistance decreases slowly with decrease in temperature, remaining at about 88% of the room temperature value at 25K. On the other hand, the Nernst coefficient decreases rapidly with decreasing temperature and becomes about 10% of the room temperature value even at 100K. The coercive field determined from these measurements also shows a strong change with temperature, increasing by a factor of two at 25K as compared with that at room temperature.</P> <P><B>Highlights</B></P> <P> <UL> <LI> Anomalous Hall and anomalous Nernst effects are measured in [CoSiB/Pt] films. </LI> <LI> Temperature dependences of the two effects show clear distinction. </LI> <LI> Sharp decrease of Nernst effect can be understood from Mott relation. </LI> </UL> </P>
Effect of grain boundaries on electrical properties of polycrystalline graphene
Park, Sanghoon,Shehzad, Muhammad Arslan,Khan, Muhammad Farooq,Nazir, Ghazanfar,Eom, Jonghwa,Noh, Hwayong,Seo, Yongho Elsevier 2017 Carbon Vol.112 No.-
<P>Since it was discovered, synthesizing large area graphene sheets by chemical or epitaxial methods is the conventional method for the application of graphene's outstanding properties. Unfortunately, CVD grown graphene is polycrystalline in nature with grain boundaries (GBs) unlike exfoliated single crystal graphene flakes. These GBs are known as the main source of degrading mechanical, chemical and electrical properties of CVD graphene. Nematic liquid crystal was employed to visualize grains and boundaries and to calculate the atomic orientation of adjacent grains. Electrical performance of various GB devices was observed, and the role of grain boundaries on the ultimate electrical performance was investigated. The same work was carried out at low temperature (similar to 7 K) to minimize the perturbation of two-dimensional electron which originated from the graphene lattice vibration. Interestingly, it was observed that there was no significant effect of the grain boundaries on the overall electrical performance of devices even at low temperature. These results lead to the conclusion that the grain boundaries in polycrystalline graphene sheets are not the cause for degradation in the electrical performance, if the grains were stitched well at the boundary in the growth process. (C) 2016 Elsevier Ltd. All rights reserved.</P>
Ehsan Elahi,Ghulam Dastgeer,Pradeep Raj Sharma,Abdul Subhan Siddiqui,Hwayong Noh 한국자기학회 2021 한국자기학회 학술연구발표회 논문개요집 Vol.31 No.2
The metal-oxides spin valve junctions are the building blocks for spintronic devices and to utilize for miniaturized magnetic sensors. Here, we describe the fabrication and characterization of vertical spin valve based on CoFe/TiO₂/CoFe structure. CoFe was deposited on Si/SiO₂ substrate and TiO₂(1 nm) deposited on CoFe directly by an e-beam evaporator, in a high vacuum. A reasonable positive magnetoresistance (MR) is obtained via this vertical spin valve at low temperatures. We have observed a maximum value of MR about 0.33% at 28K and 0.20% at 300K. At various current bias, a significant variation in MR is observed. The value of MR was high at lower current (15 μA) and then decreased for the higher bias current which saturates at 40 μA. The decrement in MR at higher bias current can be accredited to the excitation of magnons, to band bending, and probably to the contribution of interface states at higher currents. This trend was also observed in other previous reports. The linear I-V curve demonstrates the ohmic trend of the TiO₂ and FM contacts. The demonstrated device identifies TiO₂ as favorable spacer material in spin valve and opens the way to integrate high-performance memory storage devices.