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Sr2FeMoO6 nanosized compound with dielectric sheaths for magnetically sensitive spintronic devices
Nikolay Kalanda,김동현,Sergey Demyanov,유성조,Marta Yarmolich,Alexander Petrov,오석근 한국물리학회 2018 Current Applied Physics Vol.18 No.1
Single-phase agglomerated Sr2FeMoO6-d powders with the iron and molybdenum cations superstructural ordering of 88% were synthesized by sol-gel technique from the Sr(NO3)2 and Fe(NO3)3$9H2O solutions with pH ¼ 4. The ultrasound dispersion enabled us to obtain 75 nm grains. Powders were pressed with 4 GPa to receive the ceramics. The additional annealing at 700 K promoted the appearance of 7.5% SrMoO4 phase. The nanocomposite with dielectric sheaths around the grains was obtained. Magnetization temperature dependences in zero-field cooled mode revealed inhomogeneous magnetic states. At temperature below 19 K, the superparamagnetic state is observed. Temperature increase leads to a realization of the stable superparamagnetic and metastable ferrimagnetic states, blocked by magnetic anisotropy energy. The resistivity temperature dependences have the semiconducting conductivity type. The charge transfer due to the hopping conductivity on the localized states in the energy band near the Fermi level dominates at 260e300 K. At 130e200 K the charge transfer is realized by electrons tunneling through the energy barrier. The electrons inelastic tunneling on conducting channels between grains, through the localized states in the dielectic interlayer dominates at low temperatures. The resistivity decreases in magnetic fields and the negative tunneling magnetoresistive effect reaching 41% occurs.
김연중,김태우,윤종성,김명규 한국해양공학회 2019 韓國海洋工學會誌 Vol.33 No.6
Numerous deaths and substantial property damage have occurred recently due to frequent disasters of the highest intensity according to the abnormal climate, which is caused by various problems, such as global warming, all over the world. Such large-scale disasters have become an international issue and have made people aware of the disasters so they can implement disaster-prevention measures. Extensive information on disaster prevention actively has been announced publicly to support the natural disaster reduction measures throughout the world. In Japan, diverse developmental studies on disaster prevention systems, which support hazard map development and flood control activity, have been conducted vigorously to estimate external forces according to design frequencies as well as expected maximum frequencies from a variety of areas, such as rivers, coasts, and ports based on broad disaster prevention data obtained from several huge disasters. However, the current reduction measures alone are not sufficiently effective due to the change of the paradigms of the current disasters. Therefore, in order to obtain the synergy effect of reduction measures, a study of the establishment of an integrated system is required to improve the various disaster prevention technologies and the current disaster prevention system. In order to develop a similar typhoon search system and establish a disaster prevention infrastructure, in this study, techniques will be developed that can be used to forecast typhoons before they strike by using artificial intelligence (AI) technology and offer primary disaster prevention information according to the direction of the typhoon. The main function of this model is to predict the most similar typhoon among the existing typhoons by utilizing the major typhoon information, such as course, central pressure, and speed, before the typhoon directly impacts South Korea. This model is equipped with a combination of AI and DNN forecasts of typhoons that change from moment to moment in order to efficiently forecast a current typhoon based on similar typhoons in the past. Thus, the result of a similar typhoon search showed that the quality of prediction was higher with the grid size of one degree rather than two degrees in latitude and longitude.
Tran Dang Thanh,오석근,김동현,유성조,S.E. Demyanov,N.A. Kalanda,M.V. Yarmolich,L.V. Kovalev 한국물리학회 2014 Current Applied Physics Vol.14 No.6
In this work, the magnetic properties and critical behavior around ferromagneticeparamagnetic (FM ePM) phase transition in Ba1.7La0.3FeMoO6 compound have been investigated in detail. This compound exhibits a second-order magnetic phase transition with Curie temperature TC ¼ 345 K. The critical exponents b, g, and d that are determined by using the modified Arrott plots (MAP), the KouveleFisher (KF) and the critical isotherm analysis agree very well. Our results indicate a coexistence of short-range and long-range ferromagnetic (FM) interactions in Ba1.7La0.3FeMoO6 compound. The existence of long-range FM interactions in this compound can be associated with the crystal structure of materials with longrange Fe/Mo ordering parameter and strength of double-exchange interaction, whereas the existence of the short-range FM interactions can be explained by magnetic inhomogeneity and FM clusters.
Handoko, D.,Lee, S.-H.,Kalanda, N. A.,Yu, S.-C.,Oh, S. K.,Kim, D.-H.,Yang, D. S.,Petrov, A. V.,Yarmolich, M. V.,Demyanov, S. E. IEEE 2015 IEEE transactions on magnetics Vol.51 No.11
<P>We report our investigation on structural and magnetic properties of double perovskite Sr<SUB>2</SUB>FeMoO<SUB>6</SUB> (SFMO) films fabricated at different annealing temperatures. Structural properties have been investigated by means of X-ray absorption near-edge spectra and extended X-ray fine structure, where a change of oxidation state has been observed depending on the annealing temperature. It is found that the oxidation state becomes more deficient for a lower annealing temperature, indicating a lower number of unoccupied Fe states with decreasing Mo coordination number. Ordering degree of Fe and Mo ions in SFMO films is found to strongly correlate to the oxidation state, resulting in the subsequent magnetic property change.</P>