• Journal of the Korean Magnetics Society
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• v.25 no.6
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• pp.185-188
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• 2015

We have investigated nuclear magnetic resonance of $^{23}Na$ nucleus in $NaMgCl_3$ single crystal in the temperature range 200 K~410 K using FT-NMR spectrometer. The spin-lattice relaxation times $T_1$ of $^{23}Na$ nucleus residing at cubic symmetry in the host crystal was measured as a function of temperature. The $T_1$ of $^{23}Na$ nucleus decreased with increasing temperature. The nuclear spin-lattice relaxation rate $1/T_1$ of $^{23}Na$ in $NaMgCl_3$ single crystal was proportional to the temperature T. This behavior is explained with the characteristic feature of the direct process between the nuclear spins and single phonon, $1/T_1$ being proportional to the absolute temperature. The activation energy calculated was $E_a=4.82J/mol$.

• Journal of the Korean Magnetic Resonance Society
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• v.15 no.2
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• pp.146-156
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• 2011

The line widths and spin-lattice relaxation times of protons in $[N(C_2H_5)_4]_2CoCl_4$ and $[N(CH_3)_4]_2CoCl_4$ single crystals were investigated in the temperature range 160-400 K. The temperature dependences of the spin-lattice relaxation times are attributed to the molecular motions of the ethyl and methyl groups in the $[N(C_2H_5)_4]^+$ and $[N(CH_3)_4]^+$ ions respectively. The NMR line widths indicate that the ethyl groups in $[N(C_2H_5)_4]_2CoCl_4$ have one more degree of freedom than the methyl groups in $[N(CH_3)_4]_2CoCl_4$. The experimental results are interpreted in terms of the reorientations of the methyl and ethyl groups.

• Journal of the Korean Magnetic Resonance Society
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• v.14 no.2
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• pp.76-87
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• 2010

The structural phase transition of $Cs_2MnCl_4{\cdot}2H_2O$ single crystals was investigated by determining the $^{133}Cs$ spin-lattice relaxation time $T_1$. The number of resonance lines in the $^{133}Cs$ spectrum changes from seven to one near 375 K, which means that above 375 K the Cs sites are symmetric. Further, the $T_1$ of the $^{133}Cs$ nucleus undergoes a significant change near 375 K, which coincides with the change in the splitting of the $^{133}Cs$ resonance lines. The change in $T_1$ near $T_C$ is related to the loss of $H_2O$, and means that the forms of the octahedra of water molecules surrounding $Cs^+$ are disrupted.

• Journal of the Korean Magnetic Resonance Society
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• v.17 no.2
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• pp.86-91
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• 2013

Detailed information about the structural nature of three-coordinate borons in ${\beta}-BaB_2O_4$ is obtained through $^{11}B$ MAS NMR and $^{11}B$ single-crystal NMR. The three-coordinate $BO_3$ of the two borons B(1) and B(2) in ${\beta}-BaB_2O_4$ were distinguished. The spin-lattice relaxation time in the laboratory frame $T_1$ for B(1) and B(2) slowly decreases with increasing temperature, whereas the spin-lattice relaxation time in the rotating frame $T_{1{\rho}}$ for B(1) and B(2), which differs from $T_1$, is nearly constant. The B(1) and B(2) of the two types were distinguished by $^{11}B$ MAS NMR and $^{11}B$ single-crystal NMR.

• Journal of the Korean Magnetic Resonance Society
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• v.22 no.4
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• pp.107-114
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• 2018

In this exploration, the nuclear magnetic resonance of the $^{207}Pb$ nucleus in $PbWO_4:Mn^{2+}$ and $PbWO_4:Dy^{3+}$ Single Crystals using FT-NMR spectrometer is investigated. The line width of the resonance line for the $^{207}Pb$ nucleus decreases as temperature increases due to motional narrowing. The chemical shift of $^{207}Pb$ NMR spectra also increases as temperature decreases for both crystals. The spinlattice relaxation times $T_1$ of $^{39}K$ nucleus were calculated as a function of temperature (180 K~400 K). The $T_1$ of $^{207}Pb$ nucleus decreases as temperature increases. The dominant relaxation mechanism at the studied temperature range can be deduced as the Raman process, which is the coupling between lattice vibrations and the nuclear spins. This deduction is substantiated by the fact that the nuclear spin-lattice relaxation rate $1/T_1$ of the $^{207}Pb$ nucleus in $PbWO_4:Mn^{2+}$ and $PbWO_4:Dy^{3+}$ single crystal is proportional to $T^2$, or temperature squared. The activation energies for the $^{207}Pb$ nucleus in $PbWO_4:Mn^{2+}$ and $PbWO_4:Dy^{3+}$ single crystals are $E_a=49{\pm}1meV$ and $E_a=47{\pm}2meV$, respectively.

• Journal of the Korean Magnetic Resonance Society
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• v.16 no.2
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• pp.111-121
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• 2012

The spin-lattice relaxation times, $T_1$, and spin-spin relaxation times, $T_2$, of the $^{27}Al$ and $^{87}Rb$ nuclei in $RbAl(CrO_4)_2{\cdot}2H_2O$ crystals were investigated. The presence of only one resonance line for the $^{27}Al$ nuclei indicates that the results in a dynamical averaging of the crystal electric field that produces a cubic symmetry field. The changes in the temperature dependence of $T_1$ are related to variations in the symmetry of the octahedra of water molecules surrounding $Al^+$ and $Rb^+$. The $T_1$ values for the $^{27}Al$ and $^{87}Rb$ nuclei are different due to differences in the local environments of these ions. We also compared these $^{27}Al$ and $^{87}Rb$ NMR results with those obtained for $RbAl(CrO_4)_2{\cdot}2H_2O$ crystals. The relaxation mechanisms of $RbAl(XO_4)_2{\cdot}nH_2O$ (X=Cr and S) crystals are characterized by completely different NMR behaviors.

• Journal of the Korean Magnetic Resonance Society
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• v.10 no.2
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• pp.197-202
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• 2006

[ $^{11}B$ ] nuclear magnetic resonance (NMR) measurements were performed on the single crystals of $TbB_4$ to investigate local electronic structure and 4f spin dynamics. $^{11}B$ NMR spectrum, Knight shift, spin-lattice and spin-spin relaxation rates were measured down to 4K at 8T. $^{11}B$ NMR shift and linewidth are huge and strongly temperature dependent due to the 4f moments. In addition, both are proportional to magnetic susceptibility, indicating that the hyperfine field at the boron site originates from the 4f spins of Tb. Below $T_N$, the single broad resonance peak of $^{11}B$ NMR splits into several peaks reflecting the local magnetic fields due to antiferromagnetic spin arrangements. The longitudinal and the transverse relaxation rates, $1/T_1\;and\;1/T_2$, independent of temperature above $T_N$, decreases tremendously confirming huge suppression of spin fluctuation below $T_N$.

• Journal of Magnetics
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• v.1 no.1
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• pp.1-3
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• 1996

The $YBa_2Cu_3O_{7-x}$ structure has been fluorinated by a gas phase exchange technique. The ${^19}F$NMR (nuclear magnetic resonance) spin-lattice relaxation rate (1/T1) measurements on a fluorinated sample gave superconducting energy gap of $2\Delta=4.6kT_c$.

• 한국초전도학회:학술대회논문집
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• v.9
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• pp.247-250
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• 1999

We have performed $^{63,65}$Cu nuclear quadrupole resonance (NQR) measurements on Zn and Ni doped YBa$_2Cu_3O_7$ (YBa$_2Cu_{3-x}M_xO_7$, M=Zn or Ni, x = 0.00 ${\sim}$ 0.09). Doping effects are markedly different in relaxation rates as well as in superconducting transition temperatures. Both the spin-lattice and the spin-spin relaxation rates decrease for Zn doped YBCO. However, those increase for Ni doped YBCO. This contrast in local electronic dynamics provides a clear microscopic evidence that Zn forms no local moment, while Ni develops a local moment. Consequently, the antiferromagnetic spin fluctuation is suppressed by Zn doping whereas it is preserved by Ni doping.

• Elastomers and Composites
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• v.43 no.4
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• pp.259-263
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• 2008

An effect of low-temperature long-term thermal degradation on a degree of crystallinity of a low density polyethylene (LDPE) was investigated by using $^1H$ solid state nuclear magnetic resonance (SSNMR). Firstly, the long-term thermal treatment makes a color of LDPE from white to pale yellow which is indicative of thermal oxidation. Secondly, it makes the $^{1}H$ NMR spin-spin and spin-lattice relaxation times ($T_1$) to be long. Lastly, the degree of crystallinity of the semicrystalline aged-LDPE also decreases with thermal treatment. Above all, the $T_1$ increase is envisaged to be due to either a decrease of the amorphous regions governing overall spin-lattice relaxation mechanism in LDPEs or a dynamically restricted motion of specific molecular motions by intermolecular hydrogen bonding or crosslinking. However, since the decrease of crystallinity implies an increase of amorphous regions by the thermal treatment, the former case is contrast to our results. Accordingly, we concluded that the latter effect is responsible for the $T_1$ increase.