• Journal of the Korean Magnetic Resonance Society
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• v.20 no.4
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• pp.114-120
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• 2016

Nitrogen vacancy-centered diamond has recently emerged as a promising material for various applications due to its special optical and magnetic properties. In particular, its applications as a fluorescent biomarker with small toxicity, magnetic field and electric field sensors have been a topic of great interest. Recent review (R. Schirhagl et al 2014) introduced those applications using single NV-center in nanodiamond. In this minireview, I introduce the rapidly emerging DNP (Dynamic Nuclear Polarization) field using optically-pumped NV center in diamonds. Additionally, the possibility of exploiting the optically-pumped NV center for polarization transfer source, which will produce a profound impact on room temperature DNP, will be discussed.

• Bulletin of the Korean Chemical Society
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• v.8 no.2
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• pp.115-118
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• 1987

The angular dependence of polarization of the A-band emission from RbCl:$Pb^{2+}$ is measured at 13.4 K to determine the symmetry axes of the $Pb^{2+}-v^-_c$ dipoles. The results indicate that these centers posess tetragonal symmetry. This implies that $v^-_c$ is situated in the next-nearest-neighbor (nnn) position to the $Pb^{2+}$ ion. The polarization ratio of the A-band emission measured at various temperatures is found to be independent of the temperature. The temperature independence of polarization confirms that, for the ion, the Jahn-Teller effect reduced by strong spin-orbit interaction does not give rise to thermal depolarization.

• Journal of the Korean Magnetics Society
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• v.26 no.6
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• pp.179-184
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• 2016

For an industrial spin-transfer torque (STT) MRAM, low switching current and high thermal stability are required, simultaneously. For this point of view, it is essential to find magnetic materials which satisfy high spin polarization and strong perpendicular magnetocrystalline anisotropy (MCA). In this paper, we investigate electronic structures and MCA energies of perovskite $CoFeX_3$ (X = O, F, S, Cl). For X = F and Cl, spin polarization at the Fermi level are 97 % and 96 %, respectively, which are close to a half metal. Furthermore, Co-terminated 5-monolayer (ML) $CoFeX_3$ (X = O, F, S, Cl) films show perpendicular MCA. In particular, the MCA energy of the Co-terminated $CoFeCl_3$ is about 1.0 meV/cell which is three times larger than that of a 5-ML CoFe film. Therefore, we expect to realize a magnetic material with high spin polarization and strong perpendicular MCA energy by utilizing group 6 and 7 elements in the periodic table, and to contribute to commercializing of the STT-MRAM.

• Journal of the Korean Magnetics Society
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• v.17 no.5
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• pp.194-197
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• 2007

Understanding the spin polarization (P) has been an ongoing research challenge. The $Co_{1-x}Mn_x$ (x=0.27, 1) and $Co_{1-x}Fe_x$ (x=0, 0.5, 1) films were prepared using UHV-MBE system. For these films, the magnetic properties and spin polarization were investigated using SQUID and Meservey-Tedrow technique, respectively. Although measured P is uncorrelated to the bulk magnetic moment (M) in Co-Fe and Ni-Fe alloy films, it correlates with M in some alloys such as Co-Mn and Ni-Cu. The results can be understood by the tunneling currents made up of the hybridized sp-d electrons near the Fermi-energy level. Our work shows the feasibility to tailor new materials with large P values.

• Proceedings of the Korean Magnestics Society Conference
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• 2007.05a
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• pp.264.2-264.2
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• 2007

• Journal of the Korean Magnetic Resonance Society
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• v.21 no.4
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• pp.126-130
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• 2017

In the developed NMR hyperpolarization techniques, Parahydrogen-Induced Polarization (PHIP) technique is widely utilized to overcome the low sensitivity of the NMR/MRI. Parahydrogen generator is essential to produce high spin order of parahydrogen molecule. Commercial parahydrogen generator is well developed with user-friendly systems. However, it has drawbacks of long preparation time (~ 2h including cooling down time of 1h) and high cost (~ 200 million won) for the commercial setup. We designed a simple and portable parahydrogen generating system with low cost (~ 2 million won), which produce polarization in less than 1 min. With the designed parahydrogen generator, we successfully performed the PHIP with Wilkinson's catalyst on styrene. This study will broaden the parahydrogen based polarization transfer study on many researchers by providing the simple portable and low cost parahydrogen generator.

• Electrical & Electronic Materials
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• v.7 no.2
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• pp.152-156
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• 1994

The rapid thermal annealing effects of Sol-Gel derived ferroelectric PZT thin films were investigated. It was found that rapid thermal annealing(RTA) of spin coated thin films on silicon typically >$800^{\circ}C$ for about 1 min. was changed to the perovskite phase. Rapid thermally annealed films recorded maximum remanent polarization of about 5 .mu.C/cm$^{2}$, coercive field of around 30kV/cm. The switching time for polarization reversal was about 220ns. The films of RTA process showed smooth surface, and high breakdown voltages of over 1 MV/cm and resistivity of $1{\times}{10^12}$ .ohm.cm at 1 MV/cm. It was verified that the polarization reversal of the PZT film was varied partially with applying the multiple short pulse.

• Journal of Magnetics
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• v.11 no.1
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• pp.8-11
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• 2006

Recently half-metallic full-Heusler alloy films have attracted significant interests for spintronics devices. As these alloys have been known to have a high spin polarization, very large TMR ratio is expected in magnetic tunnel junctions. Among these alloys, $Co_2MnSi$ full-Heusler alloy with a high spin polarization and a high Curie temperature is considered a good candidate as an electrode material for spintronic devices. In this study, the magnetic and structural properties of $Co_2MnSi$ Heusler alloy films were investigated. TMR characteristics of magnetic tunnel junctions with a $Co_2MnSi/SiO_2/CoFe$ structure were studied. A maximum MR ratio of 39% with $SiO_2$ substrates and 27% with MgO(100) substrates were obtained. The lower MR ratio than expectation is considered due to off-stoichiometry and atomic disorder of $Co_2MnSi$ electrode together with oxidation of the electrode layer.

• Korean Journal of Materials Research
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• v.15 no.2
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• pp.121-125
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• 2005

Magnetoelectric (ME) effects for lanthanum modified $BiFeO_3-PbTiO_3\;(BE-_xPT)$ solid solutions have been investigated. The value of magnetoelectric polarization coefficient, up is 10 times greater than that of $Cr_2O_3$. The results also show that up is due to a linear coupling between polarization and magnetization, and that up is independent of do magnetic bias and ac magnetic field. The ME effect is believed to be significantly enhanced due to breaking of the cycloidal spin state of a long-period spiral spin structure, via randomly distributed charged imperfections.

• Journal of the Korean Magnetics Society
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• v.19 no.4
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• pp.133-137
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• 2009

$MnGeP_2$ thin films grown on GaAs exhibit room-temperature ferromagnetism with $T_C{\sim}$320 K, based on both magnetization and resistance measurements. The coercive fields at 5, 250, and 300 K are 3870, 1380 and 155 Oe, respectively. The anomalous Hall effect was observed, indicating spin polarization of the carriers. Hysteresis has been observed in both magnetoresistance and Hall measurements. The current-voltage characteristics of a $MnGeP_2$ film grown on an n-type GaAs substrate display semiconducting behavior.