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Proximity Effect in Superconductor/Dilute Magnetic Metal Hybrid Structures
엄종화 한국물리학회 2003 THE JOURNAL OF THE KOREAN PHYSICAL SOCIETY Vol.42 No.3
The low-temperature resistance, R(T), of narrow AuFe Kondo wires in proximity to superconducting Al lms has been measured. As the temperature, T, is lowered, R(T) shows a rapid drop below the superconducting transition of the Al lms. As the temperature is lowered further, R(T) starts to increase, eventually exceeding the normal state resistance of the AuFe wire. While the rapid drop in the high-temperature resistance can apparently be attributed to the superconducting proximity eect in AuFe wires, the behavior of the low-temperature resistance can be attributed to the Kondo eect, but is moderately suppressed by long-range superconducting pairing correlations.
Coexistence of the Kondo and the Superconducting Proximity Effects in AuFe/Al Loops
엄종화,기동건,이후종,송종한,김태곤,신윤석 한국물리학회 2006 THE JOURNAL OF THE KOREAN PHYSICAL SOCIETY Vol.48 No.3
We present measurements of the transport properties of hybrid loops consisting of a Kondo AuFe .lm and a superconducting Al .lm. The temperature dependence of the resistance and the signi.cant phase modulation of the resistance indicate the existence of the superconducting proximity eect over the range of ≫0.5 ¹m in AuFe wires with Fe concentrations of 26 ppm and 70 ppm. The magnetoresistance oscillation of AuFe/Al hybrid loops shows a reentrant behavior in temperature. The electronic phase coherence in the Kondo AuFe wires has been further con.rmed by the weak localization measurement.
Nonlocal voltage in a spin field effect transistor with finite channel width
엄종화,구현철,장준연,한석희 한국물리학회 2011 Current Applied Physics Vol.11 No.3
Spin transport in the two-dimensional electron gas with strong spin―orbit interaction is examined by using a simple phenomenological simulation. The large spin―orbit interaction and the randomized electron trajectory due to the impurity scattering make the nonlocal voltage of a spin field effect transistor undetectable in the diffusive regime. However, the spin-precessional phase accumulates coherently in the ballistic regime and the nonlocal voltage is given by a function of spin―orbit interaction parameter. If the distance between injector and detector is comparable to the mean free path, a sinusoidal oscillation of nonlocal voltage is restored even for a wide channel.
Effect of Gate Voltage on the Transport Properties in Thin Crystalline Graphite Films
오영만,엄종화 한국물리학회 2011 THE JOURNAL OF THE KOREAN PHYSICAL SOCIETY Vol.59 No.1
Graphite films are deposited on top of Si substrates from natural graphite by using mechanical exfoliation. The carrier type alternation has been confirmed by observing the Hall coefficient as a function of back gate voltage to the Si substrate. The electrons and the holes coexist at the back gate voltage (V_g) corresponding to the charge neutrality point, where the mobility and the mean free path show broad minima. The mean free time and the phase coherence time show a strong dependence on V_g. A weak localization effect is also found in the magnetoresistivity at low temperatures. However, a fit to the weak localization effect model reveals a deviation from the theoretical prefactor in the model equation for a 2-dimensional system. The weak localization effect is weakened quickly as the temperature rises above 10 K.
Gate Field Effect on Spin Transport Signals in a Lateral Spin-Valve Device
구현철,권재현,장준연,한석희,엄종화 한국물리학회 2008 THE JOURNAL OF THE KOREAN PHYSICAL SOCIETY Vol.53 No.5
The gate field effect on spin transport signals was detected in lateral ferromagnet-semiconductor hybrid devices. In the diffusive model, the change in the channel resistance induces a spin transport signal difference, but a non-local measurement shows that ΔR is almost constant with varying the gate voltage. The reason is that the spin diffusion length is slightly decreased with decreasing gate voltage due to the stronger spin-orbit interaction. At T = 20 K, the spin diffusion length can be decreased by 2.5 % by applying a gate voltage of -3 V. The gate field effect on spin transport signals was detected in lateral ferromagnet-semiconductor hybrid devices. In the diffusive model, the change in the channel resistance induces a spin transport signal difference, but a non-local measurement shows that ΔR is almost constant with varying the gate voltage. The reason is that the spin diffusion length is slightly decreased with decreasing gate voltage due to the stronger spin-orbit interaction. At T = 20 K, the spin diffusion length can be decreased by 2.5 % by applying a gate voltage of -3 V.
Large spontaneous Hall angle in [Co, CoFe/Pt] multilayer
이하나,Y.J. Cho,엄종화,S.J. Joo,신경호,김태완 한국물리학회 2010 Current Applied Physics Vol.10 No.2
We have quantitatively investigated the Hall effect in [Co, CoFe/Pt] multilayer films. The [Co, CoFe/Pt]multilayers exhibit large spontaneous Hall resistivity (ρH) and Hall angle (ρH/ρ). Even though the Hall resistivity in [Co, CoFe/Pt] multilayer films (2.7–4 × 10-7 Ω cm) is smaller than that of amorphous RE–TM alloy films which show large spontaneous Hall resistivity (<2 × 10-6 Ω cm), the Hall angle of multilayer (6–8%) is almost twice than that in amorphous rare earth–transition metal alloy films (~3%). The Hall angle provides evidence of the effects of the exchange interaction of the Hall scattering. The exchange is between conduction electron spins and the localized spins of the transition metal. The large Hall angle of [Co, CoFe/Pt] multilayer can be considered due to the high spin polarization and high Curie temperature of Co and CoFe transition metal layers. Even though the role of interfaces and surfaces in the magnetic properties of multilayer films may dominate that of the bulk, the Hall effects in [Co, CoFe/Pt]multilayer may be mainly dominated by the bulk effect.