• Korean Journal of Materials Research
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• v.26 no.1
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• pp.35-41
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• 2016

The electrical transport properties of $La_{0.5}Sr_{0.5}CrO_3$ below room temperatures were investigated by dielectric, dc resistivity, magnetic properties and thermoelectric power. Below $T_c$, $La_{0.5}Sr_{0.5}CrO_3$ contains a dielectric relaxation process in the tangent loss and electric modulus. The $La_{0.5}Sr_{0.5}CrO_3$ involves the transition from high temperature thermal activated conduction process to low temperature one. The transition temperature corresponds well to the Curie point. The relaxation mechanism has been discussed in the frame of electric modulus spectra. The scaling behavior of the modulus suggests that the relaxation mechanism describes the same mechanism at various temperatures. The low temperature conduction and relaxation takes place in the ferromagnetic phase. The ferromagnetic state in $La_{0.5}Sr_{0.5}CrO_3$ indicates that the electron - magnon interaction occurs, and drives the carriers towards localization in tandem with the electron - lattice interaction even at temperature above the Curie temperature.

• Progress in Superconductivity
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• v.12 no.1
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• pp.51-56
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• 2010

$^{13}C$ NMR (nuclear magnetic resonance) measurements have been performed to investigate the local electronic structure of a superconducting graphite intercalation compound $CaC_6$ ($T_c$ = 11.4 K). A large number of single crystals were stacked and sealed in a quartz tube for naturally abundant $^{13}C$ NMR. The spectrum, Knight shift, linewidth, and spin-lattice relaxation time $T_1$ were measured in the normal state as a function of temperature down to 80 K at 8.0 T perpendicular to the c-axis. The $^{13}C$ NMR spectrum shows a single narrow peak with a very small Knight shift. The Knight shift and the linewidth of the $^{13}C$ NMR are temperature-independent around, respectively, +0.012% and 1.2 kHz. The spin-lattice relaxation rate, $1/T_1$, is proportional to temperature confirming a Korringa behavior as for non-magnetic metals. The Korringa product is measured to be $T_1T\;=\;210\;s{\cdot}K$. From this value, the Korringa ratio is deduced to be $\xi$ = 0.73, close to unity, which suggests that the independent-electron description works well for $CaC_6$, without complications arising from correlation and many-body effects.

• Journal of the Institute of Electronics Engineers of Korea SC
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• v.42 no.2 s.302
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• pp.33-38
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• 2005

In this paper, the sensing unit of a non-invasive blood glucose sensor for home users, using a magneto-resonance absorption method, have been designed and manufactured. The sensor is capable of non-invasively determining blood glucose levels through measuring the 1H spin-lattice relaxation time in human body, The comparison of initial models, with different dimensions and shapes, for the sensing unit has led us to select the materials of the final model, which has adequate size and weight for home use. Through the design optimization using the FEM model, the dimension of final model has been determined to satisfy the required strength and uniformity of the magnetic field in the detecting area.

• Journal of the Korean Magnetic Resonance Society
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• v.26 no.1
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• pp.10-16
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• 2022

The phase transition temperatures of CsCoCl₃·2H₂O crystals are investigated via differential scanning calorimetry (DSC) and thermogravimetric analysis (TGA). Three endothermic peaks at temperatures of 370 K (=T_C1), 390 K (=T_C2), and 416 K (=T_C3) were observed for phase transitions from CsCoCl₃·2H₂O to CsCoCl₃·1.5H₂O, to CsCoCl₃·H₂O, and then to CsCoCl₃·0.5H₂O, respectively. In addition, the spin-lattice relaxation time T_1ρ in the rotating frame and T₁ in the laboratory frame as well as changes in chemical shifts for ¹H and ¹³³Cs near T_C1 were found to be temperature dependent. Our analyses results indicated that the changes of chemical shifts, T_1ρ, and T₁ are associated with structural phase transitions near temperature T_C1. The changes of chemical shifts, T_1ρ, and T₁ near T_C1 were associated with structural phase transitions, owing to the changes in the symmetry of the structure formed of H₂O and Cs⁺ ions. Consequently, the structural symmetry in CsCoCl₃·2H₂O crystals based on temperature is discussed by the environments of their H and Cs nuclei.

• Journal of the Korean Magnetic Resonance Society
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• v.2 no.1
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• pp.1-23
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• 1998

The motions of carbon-chain backbone in n-undecance and n-dodecane dissolved in CDCl3 are investigated by 13C NMR relaxation study. For this purpose a model of C - C backbone motions for these molecules is introduced that takes into account the cooperativities between rotations about two $\beta$-coupled C - C bonds. In this model it is assumed that the major conformational interconversions occurring in the inner part of the chain involve the type II jumps only, although at terminal part of the chain both type II and type III motions are assumed to take place. Information of the rate constants of these conformational transitions could be extracted by comparing the T1's calculated on the basis of the assumed model with those observed over the temperature range of 248 - 308 K. The calculations were performed according to the method proposed by Wittebort and Szabo. The activation energies, ranging from ca 12 to 20 kJ/mol, could be obtained from the Arrhenius plots of these calculated rate constants.

• Journal of Magnetics
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• v.5 no.3
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• pp.73-75
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• 2000

Undoped and Cr-doped samples of electrooptic material KTiOPO$_4$ were studied by $^{31}$P nuclear magnetic resonance (NMR). Spin-lattice relaxation time ($T_1$) measurements manifested phase transition behaviors that are attributed to changes in the dominant charge carriers in different temperature ranges.

• Bulletin of the Korean Chemical Society
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• v.21 no.11
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• pp.1071-1076
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• 2000

Temperature dependent data of 13C spin-lattice relaxation times and NOE factors for methylene carbons at 50.3MHz and 125.5 MHz have been used to probe the local chain dynamics of poly(butylene terephthalate) (PBT) in solution phase. The interpretation of the relaxation data for methylene chain carbons in PBT was attempted on the basis of several proposed motional models, among which the DLM model was found to be superior. Analysis based on the DLM model indicated that the motion of the $OCH_2groups$ was more restricted compared with the central methylene carbon, which is consistent with conclusions from solid state experiments reported by other investigators. Librational amplitudes of terminal and central carbon of PBT were estimated to be $29.84^{\circ}$ and $32.01^{\circ}respectively.

• Journal of the Korean Magnetic Resonance Society
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• v.23 no.2
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• pp.40-45
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• 2019

The phase transition temperatures and thermodynamic properties of $(NH_4)_2MnCl_4{\cdot}2H_2O$ grown by the slow evaporation method were studied using differential scanning calorimetry and thermogravimetric analysis. A structural phase transition occurred at temperature $T_{C1}$ (=264 K), whereas the changes at $T_{C2}$ (=460 K) and $T_{C3}$ (=475 K) seemed to be chemical changes caused by thermal decomposition. In addition, the chemical shift and the spin-lattice relaxation time $T_{1{\rho}}$ were investigated using $^1H$ magic-angle spinning nuclear magnetic resonance (MAS NMR), in order to understand the role of $NH_4{^+}$ and $H_2O$. The rise in $T_{1{\rho}}$ with temperature was related to variations in the symmetry of the surrounding $H_2O$ and $NH_4{^+}$.

• Journal of the Korean Magnetics Society
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• v.5 no.1
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• pp.54-57
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• 1995

We have studied the room temperature $^{1}H$ nuclear magnetic relaxation in anisotropic antiferromagnet $MnCl_{2}.4H_{2}O$ using a wide range of $^{1}H$ NMR (nuclear magnetic resonance) field. Being a system of dense paramagnetic $Mn^{++}$ ions at room temperature, $MnCl_{2}.4H_{2}O$ shows some features that can be expected from dilute paramagnetic systems, as well as some results that drastically deviate from the dilute paramagnetic approximations. Besides, $^{1}H$ nuclei exhibit an anomalous deviation in the spin-lattice relaxation time ($T_{1}$) around the field of 0.7 T.

• Korean Journal of Food Science and Technology
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• v.34 no.6
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• pp.1062-1066
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• 2002

Low field NMR was employed to discriminate the geographical origin of sesame seeds from Sudan, China, and Korea. Sudan sesame seeds had the lowest contents of moisture and crude fat. Chemical components of Korean and Chinese sesame seeds were similar, whereas relaxation times $(T_1-IR,\;T_1-SR)$ measeured through spin-lattice relaxation pluse techniques using 20 MHz NMR showed significant difference (p0.05). Canonical discriminant analysis could be used to identify the habitat of sesame seeds with over 90% accuracy of NMR results. Non-destructive and fast NMR techniques can be applied to classify Korean sesame seeds from those of other origins.