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Large magnetic anisotropy in canted antiferromagneticSr2IrO4single crystals
Hong, Yunjeong,Jo, Younjung,Choi, Hwan Young,Lee, Nara,Choi, Young Jai,Kang, Woun American Physical Society 2016 Physical Review B Vol.93 No.9
<P>The magnetocrystalline contribution to magnetic anisotropy was studied in the canted antiferromagnetic state of layered Sr2IrO4 single crystals. We performed torque measurements in magnetic fields up to 9 T under various magnetic field orientations. The strong dependence of torque on the magnetic field revealed that the magnetic easy axis is along the in-plane direction and that the observed field-induced weak ferromagnetic order is attributed only to the in-plane component of the external magnetic field. The dependence of torque on the angle produces a twofold symmetric sawtoothlike shape. A simple model consisting of canted antiferromagnetic and magnetic induction terms showed good agreement with themeasured torque. These results showthat magnetic anisotropy is closely related to the anisotropy of the exchange between antiferromagnetic moments whose canting is mediated by the Dzyaloshinsky-Moriya interaction. Our study demonstrates that torque magnetometry can be extended to the investigation of the magnetic anisotropy of complex magnetic phases.</P>
Modified torque magnetometry to determine magnetic anisotropy
Joonyoung Choi,In Hyuk Jo,Younjung Jo 한국자기학회 2021 한국자기학회 학술연구발표회 논문개요집 Vol.31 No.1
We present a novel method for magnetic anisotropy measurement using membrane-type surface stress sensor (MSS). This sensor has a silicon membrane supported by four beams incorporating piezoresistive paths [1]. We modified the on-chip aluminum interconnect on the MSS to obtain more magnetic information of the material and used it for torque measurement. Angle-dependent torque measurement of magnetic materials were preformed by rotating the device with respect to the applied magnetic field. Instead of one existing Wheatstone Bridge, we modified the on-chip aluminum interconnect to become two Wheatstone bridge circuits. These variations will allow simultaneous investigation of magnetic responses according to different crystallographic directions in a two-dimensional plane.
임은지(Eunji Lim),김봉조(Bong-Jo Kim),이철순(Cheol-Soon Lee),차보석(Boseok Cha),이소진(So-Jin Lee),서지영(Jiyeong Seo),최재원(Jae-Won Choi),이영지(Young-Ji Lee),이윤정(Younjung Lee),이동윤(Dongyun Lee) 대한노인정신의학회 2021 노인정신의학 Vol.25 No.1
Objective: To investigate perceptions of coronavirus disease-19 (COVID-19) associated with anxiety caused by the COVID-19 epidemic in the elderly who are vulnerable to mental health problems. Methods: This study used data of a survey on perceptions of COVID-19 and changes in mental health of 1,000 out of residents in a province of Korea in April 2020. The survey included questions about psychological perceptions for COVID-19. Subjects were dived into two groups (<60 and ≥60). Binary logistic regression analyses were performed for evaluating the association between anxiety and perceptions about COVID-19 in each group. Results: Results of binary logistic regression analyses revealed that only ‘fear of getting infected myself’among perceptions for COVID-19 was associated with anxiety in the elderly aged more than 60 years. However, in adults aged less than 60 years, all perceptions for COVID-19 except impairment of performance were associated with such anxiety. Conclusion: We found that the anxiety for COVID-19 in elderly with age over 60 years was associated with ‘fear of getting infected myself’ rather than ‘fear of family or people around them’, unlike adults aged less than 60 years. These results can be applied in strategies for psychological quarantine against COVID-19 among the elderly.
Dependence of superconductivity on the crystallinity of Nb films on Si wafers
Joonyoung Choi,Chang-Duk Kim,Younjung Jo 한국초전도저온공학회 2021 초전도와 저온공학 Vol.23 No.4
Among elemental metals, niobium (Nb) has the highest superconducting transition temperature (Tc) at ambient pressure. Thus, Nb films have been used in superconducting electronics and radio frequency cavity applications. In this study, the depositional factors determining the crystallinity and Tc of Nb films were investigated. An Nb film grown at a sputtering temperature of 240°C exhibited the maximum crystallinity of Nb and the minimum crystallinity of niobium oxide. X-ray photoelectron spectroscopy confirmed a maximum atomic percent of niobium and a minimum atomic percent of oxygen. A sputtering power of 210 W and a sputtering time of 50 min were the optimal conditions for Nb deposition, and the Tc of the optimized film (9.08 K) was close to that of bulk Nb (9.25 K). Transmission electron microscopy images of the thick film directly confirmed the removal of the typical in-plane compressive strain in the (110) plane caused by residual stress.
Dependence of superconductivity on the crystallinity of Nb films on Si wafers
Joonyoung Choi,Chang-Duk Kim,Younjung Jo 한국초전도저온학회 2021 한국초전도저온공학회논문지 Vol.23 No.4
Among elemental metals, niobium (Nb) has the highest superconducting transition temperature (Tc) at ambient pressure. Thus,Nb films have been used in superconducting electronics and radio frequency cavity applications. In this study, the depositionalfactors determining the crystallinity and Tc of Nb films were investigated. An Nb film grown at a sputtering temperature of 240°Cexhibited the maximum crystallinity of Nb and the minimum crystallinity of niobium oxide. X-ray photoelectron spectroscopyconfirmed a maximum atomic percent of niobium and a minimum atomic percent of oxygen. A sputtering power of 210 W and asputtering time of 50 min were the optimal conditions for Nb deposition, and the Tc of the optimized film (9.08 K) was close to thatof bulk Nb (9.25 K). Transmission electron microscopy images of the thick film directly confirmed the removal of the typicalin-plane compressive strain in the (110) plane caused by residual stress.
Changes in superconducting properties of Nb films irradiated with Kr ion beam
Minju Kim,Joonyoung Choi,Chang-Duk Kim,Younjung Jo 한국초전도저온학회 2024 한국초전도저온공학회논문지 Vol.26 No.1
This study investigated the effect of Kr ion beam irradiation on the superconducting properties of Nb thin films, which are known for their high superconducting transition temperature (T_c) at ambient pressure among single elements. Using the Stopping and Range of Ions in Matter (SRIM) program, we analyzed the distribution of Kr ions and displacement per atom (DPA) after irradiation, finding a direct correlation between irradiation amount and DPA. In samples with stronger beam energy, deeper ion penetration, fewer ions remained, and higher DPA values were observed. X-ray diffraction (XRD) revealed that the Nb (110) peak at 38.5° weakened and shifted with increasing irradiation. T_c decreased in all samples after irradiation, more significantly in those with higher beam energy. Irradiation raised resistivity of the film and lowered the residual-resistivity ratio (RRR). AC susceptibility measurements were also consistent with these findings. This research could potentially lead to more efficient and powerful superconducting devices and a better understanding of superconducting materials.
Hussain, Tayyaba,Oh, Myeong-jun,Nauman, Muhammad,Jo, Younjung,Han, Garam,Kim, Changyoung,Kang, Woun Elsevier 2018 PHYSICA B-CONDENSED MATTER - Vol.536 No.-
<P><B>Abstract</B></P> <P>We report the temperature-dependent resistivity <I>ρ</I>(<I>T</I>) of chalcogenide NiS<SUB>2-<I>x</I> </SUB>Se<SUB> <I>x</I> </SUB> (<I>x</I> = 0.1) using hydrostatic pressure as a control parameter in the temperature range of 4–300K. The insulating behavior of <I>ρ</I>(<I>T</I>) survives at low temperatures in the pressure regime below 7.5kbar, whereas a clear insulator-to-metallic transition is observed above 7.5kbar. Two types of magnetic transitions, from the paramagnetic (PM) to the antiferromagnetic (AFM) state and from the AFM state to the weak ferromagnetic (WF) state, were evaluated and confirmed by magnetization measurement. According to the temperature–pressure phase diagram, the WF phase survives up to 7.5kbar, and the transition temperature of the WF transition decreases as the pressure increases, whereas the metal–insulator transition temperature increases up to 9.4kbar. We analyzed the metallic behavior and proposed Fermi-liquid behavior of NiS<SUB>1.9</SUB>Se<SUB>0.1</SUB>.</P>