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Crystallographic and Magnetic Properties of LiCoPO4 at Low Temperature
이찬혁,김삼진,김철성 한국물리학회 2010 THE JOURNAL OF THE KOREAN PHYSICAL SOCIETY Vol.56 No.2
Polycrystalline LiCoPO4 powder was synthesized by using a solid-state reaction method. The temperature dependences of the crystallographic characteristics were analyzed by using highresolution powder neutron diffraction at various temperatures. We found that the octahedron formed with one cobalt and six oxygen ions was distorted in one direction at low temperature. Above 23 K, the distances between cobalt and each of two oxygen ions were about 2.11 °A; however at temperatures below 23 K, the distances changed to about 2.05 and 2.15 °A, respectively. The temperature dependence of the magnetization was also measured by using a superconducting quantum interference device magnetometer at temperatures ranging from 5 to 100 K. Although LiCoPO4showed an anti-ferromagnetic behavior, a rapid increase in magnetization was observed at temperatures below 8 K and a large coercivity of 335 Oe was observed at 5 K. The N´eel temperature (TN)of LiCoPO4 was determined to be 23 K.
이찬혁,전승호,채주희,왕수정,정병민,신현준,류한욱,양태호,서만욱,신병수 대한신경과학회 2017 대한신경과학회지 Vol.35 No.3
Hypereosinophilic syndrome is a rare disorder involving the eosin concentration being elevated to more than 1500/μL in the peripheral blood for 6 months, and it causes various complications in the heart, skin, and nervous and respiratory systems. The simultaneous occurrence of neurological complications of hypereosinophilic syndrome is rare. Here we report a patient with hypereosinophilic syndrome who suffered from acute cerebral infarction and peripheral neuropathy during the same period.
Neutron Diffraction and Magnetic Properties of Ba2Co2Fe12O22: Co2Y
이찬혁,임정태,김철성,김성백 한국물리학회 2013 THE JOURNAL OF THE KOREAN PHYSICAL SOCIETY Vol.62 No.12
Polycrystalline Y-type barium cobalt ferrite (Ba2Co2Fe12O22; Co2Y) was synthesized using bythe conventional ceramic method. At temperatures below 260 K, the crystal structure of Co2Y wasdetermined to be hexagonal with the space group R¯3m. It showed a soft ferrimagnetic behaviorwith Hc = 113 Oe at 297 K and the N´eel temperature (TN) was determined to be 615 K. Most of thesuper-lattice peaks of Co2Y coming from the spin structure decreased with increasing temperature. However, the super-lattice peak at 21.8 increased with increasing temperature at temperaturesabove 200 K. In addition, we observed a change in the slope of the zero-field cooled magnetizationunder a low field of 0.01 T at 215 K due to a magnetic structure transition from a helical to aferrimagnetic spin structure.
Neutron Diffraction and Mössbauer Studies of LiFePO_4
이찬혁,김철성,이인규,문승제,김삼진 한국물리학회 2011 THE JOURNAL OF THE KOREAN PHYSICAL SOCIETY Vol.58 No.3
The crystal structure of LiFePO_4 has been determined to be orthorhombic (Pnma) from neutron diffraction measuerment. The temperature dependence of the magnetization was measured by using a SQUID magnetometer. The microscopic interaction was investigated with ^57Fe Mössbauer spectroscopy. At temperature below T_N = 51 K, LiFePO_4 exhibited an anti-ferromagnetic behavior while at temperature below 23 K, we observed abrupt increase in magnetization and magnetic hyperfine field (H_(hf)). The electric quadrupole splitting (ΔE_Q) reached its maximum value at 23 K and decreases steadily with decreasing temperature below 23 K. This indicated that the orbital angular momentum L was quenched by strong crystalline field in the asymmetric octahedral structure at temperature above 23 K. ΔE_Q decreased due to spin-orbit coupling, and the orbital angular moment contribution enhances H_(hf) at temperatures below 23 K.
Heat-treatment Effect on Z-type Hexaferrite for RF Device Application
이찬혁,조광래,김철성 한국물리학회 2015 THE JOURNAL OF THE KOREAN PHYSICAL SOCIETY Vol.66 No.1
The Z-type hexaferrite Ba1.5Sr1.5Co2Fe24O41 was synthesized by using a solid state reactionmethod under various heat-treatment conditions. The crystal structure and magnetic properties athigh frequency were characterized by on x-ray diffractometer, network analyzer, vibrating samplemagnetometer, and M¨ossbauer spectrometer. The Ba1.5Sr1.5Co2Fe24O41 samples prepared by usingthe step calcination (SC12) process showed the considerably improved permeability and magneticloss compared to those prepared by using the other processes due to the complete formation of Ztypephase from the calcination. When Co2Z sample prepared by using SC12 process was sinteredat 1125 C and cooled at a slow rate, the value of magnetic loss tanμ remained below 0.1 up to750 MHz, and at 750 MHz, the values of permeability, permittivity, and dielectric loss were μ0 =7.9, "0 = 10.9, and tan" = 0.01, respectively.