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7. Microscopic control of $^{29}$Si nuclear spins near phosphorus donors in silicon

Author

Järvinen, J., Zvezdov, D., Ahokas, J., Sheludyakov, S., Vainio, O., Lehtonen, L., Vasiliev, S., Fujii, Y., Mitsudo, S., Mizusaki, T., Gwak, M., Lee, SangGap, Lee, Soonchil, and Vlasenko, L.

Subjects
Physics - Atomic and Molecular Clusters, Condensed Matter - Mesoscale and Nanoscale Physics
Abstract

We demonstrate an efficient control of $^{29}$Si nuclear spin orientation for specific lattice sites near $^{31}$P donors in silicon crystals at temperatures below 1 K and in high magnetic field of 4.6 T. Excitation of the forbidden electron-nuclear transitions leads to a pattern of narrow holes and peaks in the ESR lines of $^{31}$P. The pattern originates from dynamic polarization the $^{29}$Si nuclear spins near the donors via the solid effect. This method can be used for initialization of qubits based on $^{29}$Si nuclear spins in the all-silicon quantum computer. In comparison, polarization of $^{29}$Si performed by pumping the allowed ESR transitions, did not create any patterns. Instead, a single narrow spectral hole was burnt in the ESR line. The difference is explained by a rapid spin diffusion during the microwave pumping of the allowed transitions.

Published
2014
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8. Efficient Dynamic Polarization of Phosphorus Nuclei in Silicon in Strong Magnetic Fields and Low Temperatures

Author

Järvinen, J., Zvezdov, D., Ahokas, J., Sheludyakov, S., Vainio, O., Lehtonen, L., Vasiliev, S., Fujii, Y., Mitsudo, S., Mizusaki, T., Gwak, M., Lee, SangGap, Lee, Soonchil, and Vlasenko, L.

Subjects
Condensed Matter - Mesoscale and Nanoscale Physics
Abstract

We demonstrate that the dynamic nuclear polarization (DNP) of phosphorus donors in silicon can be very effective in a magnetic field of 4.6 T and at temperatures below 1 K. The DNP occurs due to the Overhauser effect following a cross relaxation via the forbidden flip-flop or flip-flip transitions. Nuclear polarization values $P>0.98$ were reached after 20 min of pumping with 0.4 $\mu$W of microwave power. We evaluated that the ratio of hyperfine state populations increased by three orders of magnitude after 2 hours of pumping, and an extremely pure nuclear spin system containing $<10^{-11}$ of the other spin state can be created. An inverted DNP has been obtained by pumping the low field ESR line of P followed by the flip-flip cross relaxation. This transition has much smaller relaxation rate and required substantially longer pumping times. We found that the nuclear polarization dynamics deviates substantially from a simple exponential function. The evolution of the polarization is characterized by two time constants $T^{'}_{ac}\approx$15 s in the beginning, and $T^{"}_{ac}\approx$1100 s for long pumping time. Temperature dependence of the nuclear relaxation rate of $^{31}$P was studied down to 0.75 K, below which the relaxation time became too long to be measured. The nuclear polarization followed a bi-exponential time dependence during relaxation. We suggest that the non-exponential behavior of DNP dynamics and the subsequent relaxation is mediated by the nuclei of $^{29}$Si surrounding $^{31}$P donors, which affect the transition probabilities of the forbidden cross-relaxation processes.

Published
2014
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9. Inductive Detection of Magnetostrictive Resonance

Author

Park, Jang-ik, Lee, SangGap, Yu, Insuk, and Seo, Yongho

Subjects
Condensed Matter - Other Condensed Matter
Abstract

We have developed an inductive method to detect the magnetostrictive resonance signal and applied it to an ultrasonic magnetostrictive transducer sample. Slab shaped ferrite samples are mounted in an RF coil and actuated by pulse modulated RF magnetic field. A DC magnetic field is also applied and the resonance signal from the sample is detected by the same coil after the RF field is turned off. The detector system is similar to a conventional pulse NMR system with quadrature detection. The detected signal is sensitive to the bias DC field strength and direction as well as the dimension of the sample., Comment: 4 pages 5 figures

Published
2006

11. Advancing Magnetic Field Homogeneity in 9.4 T Non-NMR Magnet With Ferromagnetic Shimming

Author

Yang, Hongmin, Jang, Jae Young, Hwang, Young Jin, Lee, SangGap, Lee, Wooseung, and Ahn, Minchul

Abstract

This study explores the possibility of achieving magnetic field homogeneity comparable to that of nuclear magnetic resonance (NMR) magnets in a low temperature superconducting (LTS) magnet originally designed for physical property measurements. The LTS magnet used in the experiment has a significant advantage due to its large spatial margin for improving the magnetic field homogeneity of the NMR magnet, as it has a room-temperature (RT) bore diameter of 102 mm. However, certain low-order gradients pose a serious problem due to the shape of the magnet. Additionally, the absence of other shimming devices, typically present in NMR magnets, makes it difficult to improve magnetic field homogeneity. This study was conducted to determine whether it is possible to overcome these limitations and upgrade the field homogeneity of the magnet solely using multiple ferromagnetic shimming technology. This research addresses the enhancement of magnetic field homogeneity by effortlessly applying ferromagnetic shimming to the non-NMR LTS magnet, which incorporates both shimming to minimize specific gradients and traditional lattice structure shimming.

Published
2024
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12. Exploring the Effects of Partial Electrical Connectors on HTS Coils: A Case Study of Insulated Coil and Paraffin-Impregnated NI Coil

Author

Lee, Wooseung, Yang, Hongmin, Park, Dongkeun, Hwang, Young Jin, Im, Chaemin, Kim, Jaemin, Hahn, Seungyong, and Lee, SangGap

Abstract

This study explores the influence of the Partial-Electrical-Connector (PEC) on High-Temperature Superconducting (HTS) coils. The PEC method emerges as a promising alternative to the conventional No-Insulation (NI) technique, establishing a direct current path between turns through partially soldered metal foils, such as copper, on the coil surface. This innovative approach achieves comparable performance to NI without necessitating a complete path between turns, offering advantages even in insulated or paraffin-impregnated coils. For the investigation, an insulated HTS coil and two NI HTS coils with paraffin impregnation are prepared. These coils undergo testing under overcurrent conditions, and their performance is compared with PEC-applied samples. The results demonstrate that coils with PEC application exhibit definitive current bypass characteristics. This finding highlights the potential of PEC to effectively create current bypass paths in both insulated and paraffin-impregnated coils.

Published
2024
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15. Analyzing the Effects of Hot-Spot Locations on the Current Bypass Characteristics in a PEC

Author

Lee, Wooseung, Yang, Hongmin, Jeong, Uijin, Jang, Jae Young, and Lee, SangGap

Abstract

A Partial Electrical Connector (PEC) offers a promising self-protection mechanism for high-temperature superconducting (HTS) coils, providing an alternative to no-insulation (NI) coils. Unlike NI coils, PEC-applied coils have limited current bypass paths, potentially limiting their self-protection capabilities. This study investigates how the location of hot-spots, created by heaters positioned at different sections within the coil, affects the performance of PEC. By analyzing voltage and center field responses, we found that the proximity of the heater to the PEC significantly influences the efficiency of current bypass. Specifically, closer hot-spots result in more effective current redirection through the PEC. These findings provide valuable insights for optimizing PEC patterns, potentially enhancing protection mechanisms for larger HTS coils by improving current bypass capabilities based on hot-spot location.

Published
2025
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19. Experimental Study of a Room-Temperature Shimming Technology Employing Genetic Algorithm for NMR/MRI Superconducting Magnets

Author

Jang, Jae Young, Hwang, Young Jin, Kim, Jaemin, Song, Seunghyun, Kim, Geonyoung, Choi, Kibum, Hahn, Seungyong, Ahn, Minchul, and Lee, SangGap

Abstract

We present a recently developed shimming method that uses a system of room-temperature (RT) orthogonal shimming coils to improve the spatial field homogeneity of high-resolution nuclear magnetic resonance (NMR) and magnetic resonance imaging (MRI) superconducting magnets. Conventional RT shimming methods require recursive routines of field mapping and RT shim coil current adjustments, which lead to a less effective and time-consuming process. In this paper, we introduce a new RT shimming method that utilizes a process of gradual and automatic search to find an optimal operating point with a genetic algorithm (GA), a type of optimization technique. The proposed algorithm is capable of determining the optimal set of currents for a system of shimming coils to create the best spatial field homogeneity by minimizing the NMR spectral linewidth. We used a commercial 600-MHz NMR magnet with a full NMR spectral linewidth at half maximum (FWHM) of 2.2 ppm, as determined by an NMR test sample contained in a cylindrical glass tube with a diameter of 5 mm to demonstrate that the shimming method can improve the FWHM to 0.15 ppm. The results demonstrate the strong potential of the proposed RT shimming methodology for the auto-shimming process of NMR/MRI applications.

Published
2023
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31. Switching through intermediate states seen in a single nickel nanorod by cantilever magnetometry.

Author

Lee, SangGap, Moore, Eric W., Hickman, Steven A., Longenecker, Jonilyn G., and Marohn, John A.

Subjects
*MAGNETIZATION, *NICKEL, *NANORODS, *CANTILEVERS, *COLD (Temperature), *MAGNETIC fields
Abstract

In-plane to out-of-plane magnetization switching in a single nickel nanorod affixed to an attonewton-sensitivity cantilever was studied at cryogenic temperatures. We observe multiple sharp, simultaneous transitions in cantilever frequency, dissipation, and frequency jitter associated with magnetic switching through distinct intermediate states. These findings suggest a new route for detecting magnetic fields at the nanoscale. [ABSTRACT FROM AUTHOR]

Published
2012
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32. Design, construction and 13 K conduction-cooled operation of a 3 T 100 mm stainless steel cladding all-REBCO magnet

Author

Jang, Jae Young, primary, Yoon, Sangwon, additional, Hahn, Seungyong, additional, Hwang, Young Jin, additional, Kim, Jaemin, additional, Shin, Kang Hwan, additional, Cheon, Kyekun, additional, Kim, Kwanglok, additional, In, Sehwan, additional, Hong, Yong-Ju, additional, Yeom, Hankil, additional, Lee, Hunju, additional, Moon, Seung-Hyun, additional, and Lee, SangGap, additional

Published
2017
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40. A Novel Fault Diagnosis Method for High-Temperature Superconducting Field Coil of Superconducting Rotating Machine.

Author

Song, Seunghyun, Ko, Tae Kuk, Choi, Yojong, and Lee, SangGap

Subjects
ROTATING machinery, SUPERCONDUCTING coils, FAULT diagnosis, FAST Fourier transforms, DIAGNOSIS methods, POWER resources
Abstract

In this paper, a new method is presented for sensitive quench detection in high-temperature superconductor (HTS) rotating machinery. The normal zone propagation velocity of an HTS is about 1000 times slower than that of a low-temperature superconductor. Therefore, the propagation of normal zone resistance, which occurs when the HTS transits from the superconducting state to the normal state, is also slower. Thus, it is difficult to detect the abnormal signals by voltage measurement using voltage taps. Moreover, the monitoring signal includes noise generated by interaction between the HTS rotating machinery and the industrial environment. Therefore, when quenching occurs in the HTS rotating machinery, a thermal runaway occurs in the hot spot. Furthermore, the magnetic energy stored in the HTS coil can damage the machinery. For these reasons, a new method is proposed for sensitive quench detection that reduces the noise generated from the power supply and from the HTS rotating machinery, using both an RLC resonance circuit and fast Fourier transform analysis. [ABSTRACT FROM AUTHOR]

Published
2020
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47. Microscopic control ofSi29nuclear spins near phosphorus donors in silicon

Author

Järvinen, J., primary, Zvezdov, D., additional, Ahokas, J., additional, Sheludyakov, S., additional, Vainio, O., additional, Lehtonen, L., additional, Vasiliev, S., additional, Fujii, Y., additional, Mitsudo, S., additional, Mizusaki, T., additional, Gwak, M., additional, Lee, SangGap, additional, Lee, Soonchil, additional, and Vlasenko, L., additional

Published
2015
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48. Efficient dynamic nuclear polarization of phosphorus in silicon in strong magnetic fields and at low temperatures

Author

Järvinen, J., primary, Ahokas, J., additional, Sheludyakov, S., additional, Vainio, O., additional, Lehtonen, L., additional, Vasiliev, S., additional, Zvezdov, D., additional, Fujii, Y., additional, Mitsudo, S., additional, Mizusaki, T., additional, Gwak, M., additional, Lee, SangGap, additional, Lee, Soonchil, additional, and Vlasenko, L., additional

Published
2014
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50. Sustainable Method for the Large-Scale Preparation of Fe3O4 Nanocrystals.

Author

Lee, SungWoo, Yoon, Jae‐Sik, Kang, Sungkyoung, Kwon, Kihyun, Chang, Ki Soo, Lee, SangGap, Choi, Sang‐Il, Jeong, Jong‐Ryul, Lee, Gaehang, Nam, Ki Min, and Davies, P.

Subjects
NANOCRYSTAL synthesis, IRON oxides, DECANOL, THERMAL analysis, CHEMICAL decomposition, POROUS materials
Abstract

In this work, a facile synthetic process is reported for the large-scale synthesis of Fe3O4 nanocrystals. Thermal decomposition of Fe(acac)3 (100 g) in 1-hexadecanol produced Fe3O4 nanocrystals with well-controlled sizes and morphologies. The nanocrystals were spherically shaped with average diameters of 7.8 ± 0.6, 6.5 ± 0.4, and 5.9 ± 0.2 nm when prepared at 300°C, 270°C, and 250°C, respectively. Mechanisms of crystal formation were elucidated on the basis of gas chromatography-mass spectroscopy analysis, enabling the large-scale preparation of Fe3O4 nanocrystals. To provide an environmentally benign route, Fe3O4 nanocrystals were prepared with recycled solvent which was recovered from the initial experiment. The resulting porous Fe3O4 nanocrystals had larger average sizes than those of the initial nanocrystals. Structural characterization was performed using transmission electron microscopy and powder X-ray diffraction. [ABSTRACT FROM AUTHOR]

Published
2016
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