• 한국초전도저온공학회:학술대회논문집
• /
• 한국초전도저온공학회 2003년도 추계학술대회 논문집
• /
• pp.240-242
• /
• 2003

The properties of superconductor bearing are depend on shape of rotor, especially thickness of ferromagnetic shim between permanent magnets. The levitation forces and stiffness of superconductor bearings as the thickness of the ferromagnetic shim were calculated and measured, Frozen image model and difference of magnetization per unit volume of the superconductor were used to calculate stiffness for two models. The calculated values had similar trend with the measured one. From the results, an optimal design of the rotor was selected.

• 한국자기학회지
• /
• 제22권2호
• /
• pp.66-72
• /
• 2012

강자성 초전도체의 발견은 상극으로 알려진 강자성과 초전도성이 어떻게 상호작용하여 조화롭게 공존하는지에 대한 학문적인 연구뿐만 아니라 새로운 기술적인 응용을 위한 광범위한 탐구를 이끌고 있다. 본 해설논문에서는 강자성 초전도체에 대한 이해를 돕기 위하여, 먼저 초전도체의 쿠퍼쌍을 깨뜨리는 강한 자기장의 궤도 효과와 상자성 효과에 대하여 설명한다. 자기장의 이러한 효과 이외에도 초전도체/강자성체 복합 구조의 계면에서 발생하는 근접 효과에 의해 단일상 쿠퍼쌍은 강자성체를 지나가는 동안 불안정하여 아주 짧은 침투깊이를 가진다. 그러나 쿠퍼쌍이 홀-진동수 삼중상인 경우 안정되고 긴 유효길이를 가지게 되는데, 새로운 스핀 전자소자로서의 개발을 위해 그 연구의 중요성이 높아지고 있다. 마지막으로 다양한 강자성 초전도체와 양자구속효과에 의해 두 성질이 공존하는 저차원의 물질들을 소개한다.

• Progress in Superconductivity
• /
• 제2권1호
• /
• pp.43-46
• /
• 2000

We report on the tunneling spectroscopy of tunnel junctions using d-wave superconductor in relation to Andreev reflection. The zero bias conductance peak (ZBCP) which has maximum on [110] direction of ab-plane is observed on metal $Au/YBa_2Cu_3O_y$ tunnel junctions while it is suppressed on the ferromagnetic $Co/Au/YBa_2Cu_3O_y$ tunnel junctions. The effects of Andreev reflection on the differential conductance of each junction are dependent on the tunnel direction. For the $Co/Au/YBa_2Cu_3O_y$ junction, the suppression of Andreev reflection takes place by spin-polarized quasiparticles tunneling from a ferromagnetic material to a d-wave superconductor. By comparing these experimental results with recent theoretical works on Andreev reflection, the existence of Andreev bound state due to the d-wave symmetry of the pair potential is verified in high-$T_c$ superconductor.

• 한국초전도ㆍ저온공학회논문지
• /
• 제18권1호
• /
• pp.33-36
• /
• 2016

Suppression of the superconducting transition temperature ($T_c$) of NbN thin films in superconductor/ferromagnet multilayers has been investigated. Both superconducting NbN and ferromagnetic FeN layers were deposited on thermally oxidized Si substrate at room temperature by using reactive magnetron sputtering in an $Ar-N_2$ gas mixture. The thickness of FeN films was fixed at 20 nm, while the thickness of NbN films was varied from 3 nm to 90 nm. $T_c$ suppression was clearly observed in NbN layers up to 70 nm thickness when NbN layer was in proximity with FeN layer. For a given thickness of NbN layer, the magnitude of $T_c$ suppression was increased in the order of Si/FeN/NbN, Si/NbN/FeN, and Si/FeN/NbN/FeN structure. This result can be used to design a spin switch whose operation is based on the proximity effect between superconducting and ferromagnetic layers.

• 한국초전도ㆍ저온공학회논문지
• /
• 제18권2호
• /
• pp.5-7
• /
• 2016

We present an experimental investigation of the superconducting transition temperatures, $T_c$, of superconductor/ferromagnet bilayers with varying the thickness of ferromagnetic layer. FeN was used for the ferromagnetic (F) layer, and NbN and Nb were used for the superconducting (S) layer. The results were obtained using three different-thickness series of the S layer of the S/F bilayers: NbN/FeN with NbN thickness, $d_{NbN}{\approx}9.3nm$ and $d_{NbN}{\approx}10nm$, and Nb/FeN with Nb thickness $d_{Nb}{\approx}15nm$. $T_c$ drops sharply with increasing thickness of the ferromagnetic layer, $d_{FeN}$, before maximal suppression of superconductivity at $d_{FeN}{\approx}6.3nm$ for $d_{NbN}{\approx}10nm$ and at $d_{FeN}{\approx}2.5nm$ for $d_{Nb}{\approx}15nm$, respectively. After shallow minimum of $T_c$, a weak $T_c$ oscillation was observed in NbN/FeN bilayers, but it was hardly observable in Nb/FeN bilayers.

• 한국초전도학회:학술대회논문집
• /
• 한국초전도학회 2000년도 High Temperature Superconductivity Vol.X
• /
• pp.141-144
• /
• 2000

We report on the influence of d-wave pairing symmetry in high-T$_c$ superconductor by tunneling spectroscopy. The zerobias conductance peak(ZBCP) which is produced by tunneling through the ab-plane is observed on both of metal Au/YBa$_2$Cu$_3$O$_y$(N/S) tunnel junctions and ferromagnet Co/Au/ YBa$_2$Cu$_3$O$_y$(F/N/S) tunnel junctions. The effects of Andreev reflection on the differential conductance of each junctions are dependent on the tunnel direction. For the S/N/F junction, it appears the suppression of the ZBCP due to the suppression of Andreev reflection at the interface between a ferromagnetic material and a d-wave superconductor. By comparing these experimental results with recent theoretical works on Andreev reflection, the existence of Andreev bound state is verified in high-T$_c$ superconductor, due to the d-wave symmetry of the pair potential.

• 한국초전도학회:학술대회논문집
• /
• 한국초전도학회 2003년도 High Temperature Superconductivity Vol.XIII
• /
• pp.9-9
• /
• 2003

• Progress in Superconductivity
• /
• 제3권1호
• /
• pp.70-73
• /
• 2001

We report the spin injection and transport properties of three terminal devices of Co/Au/$YBa_2$$Cu_3$$O_{y}$(F/N/S) tunnel junctions by injection of spin-polarized quaiparticles using a cobalt ferromagnetic injector. The observed current gain depends on the thickness of Au interlayer and is directly related to the nonequilibrium magnetization due to spin relaxation effects. The tunnel characteristic of a F/N/S tunnel junctions exhibited a zero bias conductance peak (ZBCP). The suppression of the ZBCP was observed due to the suppression of Andreev reflection at the interface, which is due to the spin scattering processes at the interface between a ferromagnetic and a d-wave superconductor.r.

• 한국초전도학회:학술대회논문집
• /
• 한국초전도학회 1999년도 High Temperature Superconductivity Vol.IX
• /
• pp.200-205
• /
• 1999

In the ferromagnetic phase with electrons for La$_{1-x}$(Ca or Sr)$_x$MnO$_3$, films, a remnant resistivity of the order of 10$^{-8}$ ${\omega}$m is observed up to 100 K and increases exponentially with temperature up to T$_c$ and above one Tesla as a function of magnetic field strength (a positive magnetoresistivity). The phase below T$_c$ is regarded as a polaronic state with a polaronic tunneling conduction. Possible p-wave condensation (or superconductor) with a parabolic density of states and the phase separation are discussed on the basis of the two-fold degeneracy of ${\varrho}_{\delta}$ orbitals.

• Journal of Magnetics
• /
• 제13권4호
• /
• pp.128-131
• /
• 2008

We have investigated the electronic structures and magnetic properties of both undoped and doped bcc Ni using the full-potential linearized augmented plane wave (FLAPW) band method. A ferromagnetic ground state is obtained at the equilibrium volume of bcc Ni. When the system is under strain, the nonmagnetic ground state is stabilized. When the Ni is doped with V, the $Ni_{16-x}V_x$ material loses its magnetic properties when x > 2. We have also discussed the possible superconducting properties of $Ni_{16-x}V_x$.