Jeong-Woo Sohn
KAIST
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Featured researches published by Jeong-Woo Sohn.
Applied Physics Letters | 2013
Hyon-Seok Song; Kyeong Dong Lee; Jeong-Woo Sohn; See-Hun Yang; Stuart S. P. Parkin; Chun-Yeol You; Sung-Chul Shin
We investigate the intrinsic Gilbert damping constant in perpendicular magnetic anisotropy Co/Ni multilayer system by means of an all-optical method. We find that the intrinsic Gilbert damping constant does not depend on the stack number and the perpendicular magnetic anisotropy when the magnetic field is high enough. In contrast, the extrinsic Gilbert damping is strongly correlated with the inhomogeneous anisotropy distribution in the low-field regime, as observed in magneto-optical images. Intriguingly, the extrinsic Gilbert damping is consistently reduced with decreasing length scale in the measurements, providing a concrete means to determine the intrinsic Gilbert damping.
Applied Physics Letters | 2013
Hyon-Seok Song; Kyeong-Dong Lee; Jeong-Woo Sohn; See-Hun Yang; Stuart S. P. Parkin; Chun-Yeol You; Sung-Chul Shin
The relationship between Gilbert damping and magneto-crystalline anisotropy is studied here using an all-optical method in a perpendicular Co/Ni multilayer system by varying the Ti-buffer thickness. As the Ti-buffer thickness increases, the magneto-crystalline anisotropy is enhanced. The time-resolved Kerr signal of each sample is well described by its own intrinsic Gilbert damping constant in a wide range of the external magnetic field. Interestingly, we find that Gilbert damping constants increase linearly from 0.021 to 0.036 when the magneto-crystalline anisotropy of the samples varies from 2.4 to 3.4 Merg/cm3. Such a linear relationship implies that the spin-orbit interaction is the main source of the damping process through spin-lattice relaxation in our system.
Applied Physics Letters | 2011
Ji-Wan Kim; Hyon-Seok Song; Jae-Woo Jeong; Kyeong-Dong Lee; Jeong-Woo Sohn; T. Shima; Sung-Chul Shin
We have investigated the ultrafast magnetization dynamics of L10-ordered Fe50Pt50 thin film by means of a time-resolved magneto-optical Kerr effect measurement. We have found a high Gilbert damping value of α∼0.26, together with a very high precession frequency of f∼85 GHz and the shortest relaxation characteristic time of τ∼6.5 ps ever reported. We believe that L10-ordered FePt film with the unique property of a very high precession frequency and the shortest relaxation time will be very useful for the realization of picosecond spin switching.
Scientific Reports | 2015
Kyeong-Dong Lee; Dong-Jun Kim; Hae Yeon Lee; Seung-Hyun Kim; Jong-Hyun Lee; Kyung-Min Lee; Jong-Ryul Jeong; Ki-Suk Lee; Hyon-Seok Song; Jeong-Woo Sohn; Sung-Chul Shin; Byong Guk Park
The utilization of ferromagnetic (FM) materials in thermoelectric devices allows one to have a simpler structure and/or independent control of electric and thermal conductivities, which may further remove obstacles for this technology to be realized. The thermoelectricity in FM/non-magnet (NM) heterostructures using an optical heating source is studied as a function of NM materials and a number of multilayers. It is observed that the overall thermoelectric signal in those structures which is contributed by spin Seebeck effect and anomalous Nernst effect (ANE) is enhanced by a proper selection of NM materials with a spin Hall angle that matches to the sign of the ANE. Moreover, by an increase of the number of multilayer, the thermoelectric voltage is enlarged further and the device resistance is reduced, simultaneously. The experimental observation of the improvement of thermoelectric properties may pave the way for the realization of magnetic-(or spin-) based thermoelectric devices.
Applied Physics Letters | 2012
Sung Kim; Jeong-Woo Sohn; H.J. Kim; JiYeon Ku; Y. J. Park; Seung-nam Cha; Jong Min Kim
A theoretical model for the radially dependent effective piezoelectric coefficient and corresponding piezoelectric potential in intrinsic ZnO nanowires (NWs)/nanotubes (NTs) is presented. Substrate-bound ZnO structures oriented along the c-axis with diameters of 100–5000 nm (NWs) and inner diameters of 100–900 nm (NTs; fixed outer diameter, 1000 nm) were examined using finite element method analysis. The piezoelectric potential depended nonlinearly on the NT/NW size, which we explain using the effective piezoelectric coefficient and peak piezoelectric potentials. We propose that this coefficient can be used to judge the degree of enhancement of the piezoelectric potential in ZnO NWs/NTs.
Applied Physics Express | 2014
Kyeong-Dong Lee; Hyon-Seok Song; Ji-Wan Kim; Hyun Seok Ko; Jeong-Woo Sohn; Byong-Guk Park; Sung-Chul Shin
The magnetization dynamics of perpendicularly magnetized FePt films is studied using both magnetic-field-induction and all-optical methods. A critically damped trajectory was observed in this system, where the precession ended within subnanoseconds after a single large oscillation. Using the Landau?Lifshitz?Gilbert (LLG) calculation with an experimental configuration, the effective anisotropy and damping constant were obtained. A damping constant of approximately 0.2 was determined after both a magnetic field and a laser pulse were used. The laser-induced real-space trajectory was well explained by the modified LLG calculation taking into account the demagnetization and time-dependent anisotropy.
Applied Physics Express | 2015
Hyon-Seok Song; Kyeong-Dong Lee; Chun-Yeol You; See-Hun Yang; Stuart S. P. Parkin; Byong Guk Park; Jeong-Woo Sohn; Jung-Il Hong; Sung-Chul Shin
We studied the intrinsic and extrinsic Gilbert damping constants measured with an all-optical method in an exchange-biased IrMn/Cu/CoFe trilayer system with various Cu-spacer layer thicknesses. To understand the effect of the exchange bias on damping, the strength of the exchange bias was controlled by the Cu-spacer layer. When the external magnetic field is high enough compared with the exchange fields, the intrinsic Gilbert damping constant is independent of the exchange bias field. On the other hand, under a low external magnetic field, the extrinsic Gilbert damping is dominant because of the magnetic inhomogeneities, and is strongly correlated with the exchange bias field.
Current Applied Physics | 2016
Jeong-Woo Sohn; Hyon-Seok Song; Ji-Wan Kim; Il-Jae Shin; Byoung-Chul Min; Chun-Yeol You; Sung-Chul Shin
Current Applied Physics | 2016
Hyon-Seok Song; Kyeong-Dong Lee; See-Hun Yang; Jeong-Woo Sohn; Hyun Joong Kim; Chun-Yeol You; Byong-Guk Park; Stuart S. P. Parkin; Sung-Chul Shin; Jung-Il Hong
한국자기학회 학술연구발표회 논문개요집 | 2014
Kyeong-Dong Lee; Dong-Jun Kim; Byong-Guk Park; Seung-Hyun Kim; Jong-Hyun Lee; Jong-Ryul Jeong; Ki-Suk Lee; Hyon-Seok Song; Jeong-Woo Sohn; Sung-Chul Shin