• Journal of the Korean Magnetics Society
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• v.22 no.2
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• pp.66-72
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• 2012

The findings of ferromagnetic superconductor have attracted much attention not only for fundamental research to investigate how the antagonistic properties of ferromagnetism and superconductivity coexist peacefully but also for potential technological applications. Firstly, in order to help for understanding the ferromagnetic superconductor, I have explained the orbital and paramagnetic pair-breaking effects of magnetic field, which breaks the superconducting Cooper pairs. In addition to such effects of magnetic field, the singlet Cooper pairs become unstable upon going through the ferromagnetic materials by the proximity effect. The proximity effect occurs at the interface of thin films composing of superconductor and ferromagnet and leads to have very short penetration depth of Cooper pairs. However, a type of odd-frequency triplet in comparison with the singlet could be very stable and has a longer effective depth. It needs to be explored for the innovative spintronic devices. Finally, various ferromagnetic superconductors coexist and the lower-dimensional materials under the Quantum confinement effect have been introduced.

• Journal of the Korean Magnetics Society
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• v.9 no.6
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• pp.312-320
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• 1999

Effect of deposition conditions on the magnetic properties of SmCo/Cr prepared by a RF magnetron sputtering method was studied. We obtained the maximum coercivity of 3.2 kOe in the sample of Cr(50 nm)/SmCo(40 nm, 50W, 20 mT)/Cr(150 nm, 100 W, 30 mT). The coercivity of the SmCo/Cr depends largely on the roughness of the Cr underlayer and the composition of SmCo. The roughness of the Cr underlayer increased with increasing the Ar pressure and thickness, and promoted the isolation of SmCo grains which resulted in an enhanced coercivity. The composition of the SmCo was changed with RF power and Ar pressure due to the mass difference between Sm and Co and the resputtering phenomena. The maximum coercivity was obtained in the composition of about 20 at.% Sm. The mechanism of magnetization reversal of the present SmCo films changed from domain wall motion to domain rotation as the RF power and the Ar pressure increase. This was though to be due to the defects, such as the roughness of Cr surface, porous column boundaries etc., which inhibit domain wall movement.

• Journal of the Korean Magnetics Society
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• v.9 no.3
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• pp.159-165
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• 1999

Structural, magnetic and magnetoresistance behavior of NiFe/Ag multilayers prepared by a magnetron sputter under an Ar and $Ar/H_2$ atmosphere was studied. It was difficult to make a uniform multilayer by using an Ar atmosphere. However, the uniform multilayers could be fabricated by using an $Ar/H_2$ atmosphere. This was thought to be due to decrease in the energy of the sputtered atom and Ar content of the film. Typical magnetoresistance behavior of the discontinuous NiFe/Ag multilayers appeared when the uniform multilayer was formed and annealed. Substrate temperature did not improve the uniformity of the multilayers. Above 20$0^{\circ}C$ of the substrate temperature, the films were almost formed into granular alloys rather than multilayers.

• Journal of the Korean Magnetics Society
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• v.21 no.6
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• pp.204-207
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• 2011

We developed a time-resolved magneto-optical Kerr effect microscope system to investigate ultrafast magnetization dynamics. Based on the pump-probe method, 0.1-ps time resolution was achieved by use of a fs Ti:Sapphire laser. The magnetization dynamics was then measured on Pt/Co/Pt thin films with various Co thicknesses. All the samples exhibited ultrafast demagnetization within a few ps by direct heating of pump laser. Some thicker samples showed precessional motion of magnetization, from which the Gilbert damping constant was determined based on the Landau-Lifshitz-Gilbert equation.

• Journal of the Korean Magnetics Society
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• v.6 no.6
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• pp.405-410
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• 1996

Valence band photoemission spectroscopy (PES) measurements have been performed for $Co_{x}Pd_{100-x}$ alloy films using synchrotron radiation (x = 0, 25, 40, 65). Then the partial spectral weight distributions (PSW's) of Co 3d and Pd 4d electrons have been determined. The Co 3d PSW's exhibit some structures which are quite different from those of the Co film for x < 25 %, whereas they become very similar to those of the Co film for x > 40 %. For x < 25 %, the peak near the Fermi level ($E_F$) and a shoulder around 2 eV binding energy in the Co 3d PSW reflect large hybridization between Pd 4d and Co 3d electrons, suggesting that the hybridization might play an inportant role in determining perpendicualr magnetic anisotropy. The Pd 4d PSW's in Co-Pd alloy films are found to have larger FWHM's (full widths at half maximum), larger binding energies of the main peaks, and larger spectral intensities at $E_F$ than the PES spectrum of the Pd film. The FWHM of the Pd 4d PSW increases with decreasing Pd concentration, which are considered to reflect the disordering effect in the alloy formation or the change in the Pd 4d electronic structure due to hybridization between Co 3d and Pd 4d electrons.

• Journal of the Korean Magnetics Society
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• v.7 no.4
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• pp.191-195
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• 1997

$Co_{84}Hf_{16}$ (1300$\AA$, 2150$\AA$) thin films were prepared by dc magnetron sputtering method. To investigate the uniaxial anisotrpy of the sample, the saturation and effective magnetization of the thin films were measured by VSM and FMR, respectively. The spectroscopic splitting g factor were estimated from the ferromagnetic resonance curves. For 1300$\AA$, 2150$\AA$, the effective magnetization was measured at the temperatures from T=77K to T=300K. The results were analyzed in terms of Bloch's law $M_s(T)=M_s(0)(1BT^{3/2}CT^{5/2}$. The Bloch coefficient B and C were determined by fitting. $M_{eff}(0)$ was obtained by extrapolating $M_{eff}$ to 0 K. From this result, the spinwave stiffness constants D was also determined and the exchange stiffness constants $A_{eff}$ were calculated by Kittel's resonance conditions.

• Journal of the Institute of Electronics Engineers of Korea SC
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• v.45 no.4
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• pp.29-34
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• 2008

Generally, for conventional 3-D Hall sensor it is general that the sensitivity for $B_z$ is about 1/10 compared with those for $B_x$ or $B_y$. Therefore, in this work, we proposed 3-D Hall sensor with new structures. We have increased the sensitivity about 6 times to form the trench using anisotropic etching. And we have increased the sensitivity for the $B_z$ by 80 % compared with those of $B_x$ and $B_y$ using deposition of the ferromagnetic thin films on the bottom surface of the wafer to concentrate the magnetic fluxes. Sensitivities of the fabricated sensor with Ni/Fe film for $B_x,\;B_y$, and $B_z$ were measured as 361mV/T, 335mV/T, and 286mV/T, respectively. It has also showed sine wave of Hall voltages over a $360^{\circ}$ rotation. A packaged sensing part was $1.2{\times}1.2mm^2$. The measured linearity of the sensor was within ${\pm}3%$ of error. Resolution of the fabricated sensor was measured by $1{\times}10^{-5}T$.

• Journal of the Korean Magnetics Society
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• v.24 no.2
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• pp.35-40
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• 2014

We investigate magnetism and magnetocrystalline anisotropy of CoFe thin films, using VASP code in GGA. In this study Co-terminated and Fe-terminated 5-layer CoFe thin films are employed. The Co-terminated CoFe thin film shows two total energy minima at 2-dimensional lattice constants of $2.45{\AA}$ and $2.76{\AA}$. The film of $2.45{\AA}$ has fcc-like structure and the film of $2.76{\AA}$ has bcc-like structure similarly to a bulk CoFe alloy. And the fcc-like film is more stable by the energy difference of about 160 meV compared to the bcc-like film. The Fe-terminated CoFe film shows very complicated behaviour of total energy which is suspected to be closely related to its complex magnetic structure. The Co-terminated CoFe film of $2.76{\AA}$ shows perpendicular magnetocrystalline anisotropy (MCA), while the film of 2.45 does parallel MCA. The Fe-terminated CoFe film also exhibits similar MCA behaviour.

• Proceedings of the Korean Vacuum Society Conference
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• 2010.02a
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• pp.14-15
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• 2010

Recently there has been growing interest in topological insulators or the quantum spin Hall (QSH) phase, which are insulating materials with bulk band gaps but have metallic edge states that are formed topologically and robust against any non-magnetic impurity [1]. In a three-dimensional material, the two-dimensional surface states correspond to the edge states (topological metal) and their intriguing nature in terms of electronic and spin structures have been experimentally observed in bulk Bi1-xSbx single crystals [2,3,4]. However, if we want to know the transport properties of these topological metals, high purity samples as well as very low temperature will be needed because of the contribution from bulk states or impurity effects. In a recent report, it was also shown that an intriguing coupling between the surface and bulk states will occur [5]. A simple solution to this bothersome problem is to prepare a topological metal on an ultrathin film, in which the surface-to-bulk ratio is drastically increased. Therefore in the present study, we have investigated if there is a method to make an ultrathin Bi1-xSbx film on a semiconductor substrate. From reflection high-energy electron diffraction observation, it was found that single crystal Bi1-xSbx films (0${\sim}30\;{\AA}A$ can be prepared on Si(111)-$7{\times}7$. The transport properties of such films were characterized by in situ monolithic micro four-point probes [6]. The temperature dependence of the resistivity for the x=0.1 samples was insulating when the film thickness was $240\;{\AA}A$. However, it became metallic as the thickness was reduced down to $30\;{\AA}A$, indicating surface-state dominant electrical conduction. Figure 1 shows the Fermi surface of $40\;{\AA}A$ thick Bi0.92Sb0.08 (a) and Bi0.84Sb0.16 (b) films mapped by angle-resolved photoemission spectroscopy. The basic features of the electronic structure of these surface states were shown to be the same as those found on bulk surfaces, meaning that topological metals can be prepared at the surface of an ultrathin film. The details will be given in the presentation.

• Journal of the Korean Magnetics Society
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• v.8 no.6
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• pp.380-387
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• 1998

In this paper, a sensor material with Fe/Zr multilayer thin film, in which the change in the magnetization and strain with hydrogenation is maximized, were developed. Compositionally modulated (CM) Fe/Zr multilayers with a $Fe_{80}Zr_{20}$ composition and modulation wavelengths ($\lambda$) $3~50{\AA}$ were deposited by sequentially sputtering (RF diode) elemental Fe and Zr targets. The films were electrolytically hydrogenated to select the optimum Fe/Zr multilayers that show the maximum increases in the magnetization and strain with hydrogenation. The changes in the magnetic properties of the thin films after hydrogenation, were measured using a hysteresis graph and a vibrating sample magnetometer (VSM), and the strains induced in the films by hydrogenation were also measured using a laser heterodyne interferometer (LHI). The optimum sensor material selected was incorporated in a fiber-optic hydrogen sensor (that can sense indirectly amount of hydrogen injected) by depositing it directly on the sensing arm of a single-mode fiber Michelson interferometer. The developed sensor holds significant promise for non-destructive test evaluation (NDE) applications because it is expected to be useful for detecting easily and accurately the subsurface corrosion in structural systems.