Topic
Nuclear quadrupole resonance
About: Nuclear quadrupole resonance is a research topic. Over the lifetime, 3531 publications have been published within this topic receiving 38801 citations. The topic is also known as: Nuclear quadrupole resonance spectroscopy & NQR.
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TL;DR: In this paper, the properties of hydrogen defect centers in two group III nitrides, AlN and GaN, and relevant studies by µSR spectroscopy were reviewed. But the results obtained by a form of nuclear quadrupole resonance were not considered.
Abstract: This paper reviews recent work on the properties of hydrogen defect centres in two group III nitrides, AlN and GaN, and relevant studies by µSR spectroscopy, i.e. muon spin rotation, relaxation and resonance. We highlight, especially, results obtained by a form of nuclear quadrupole resonance. Implanted positive muons are used to mimic and model the behaviour of interstitial protons. The resultant defect centres exhibit both metastability and bistability. In AlN, they remain as positive ions but partition themselves between a highly mobile species and one that is trapped and immobilized to temperatures as high as 800 K in cage-like sites adjacent to nitrogen. The barrier to escape from the cage is 0.86 eV. In n-type GaN, the cage-site positive ions are stable only up to 200 K; above this temperature they capture electrons to convert to negatively charged centres, analogues of hydride ions, relocating to sites antibonding to gallium. These latter escape from the cage sites around 600 K with an activation energy of 1.5 eV to join more mobile negative ions diffusing via channel sites with an activation energy of 0.65 eV. Data on the neutral paramagnetic centre suggest that hydrogen can act as a shallow-donor in at least one other member of this family of materials, namely InN.
11 citations
TL;DR: In this article, the temperature dependence of the nuclear quadrupole resonance frequency νQ and spin-lattice relaxation time T1 of the 35Cl nuclei in powdered samples of K2PdCl6 were measured.
Abstract: Measurements of the temperature dependence of the nuclear quadrupole resonance frequency νQ and spin–lattice relaxation time T1 of the 35Cl nuclei in powdered samples of K2PdCl6 are reported. The d...
11 citations
TL;DR: In this article, a close relationship between the magnetic ordering and the structural disorder in the Al layers isolated from the Pd layers is demonstrated, and it is pointed out that the exchange coupling via the al layers along the c-axis, which leads to the AF ground state, critically depends on the occupation and distribution of Al atoms.
Abstract: Systematic measurements of the NQR spectrum and the nuclear-spin-lattice relaxation rate, 1/ T 1 , of 27 Al in the heavy-fermion antiferromagnetic (AF) compound CePd 2 Al 3 have revealed that the magnetic nature dramatically changes from showing long-range and inhomogeneous AF ordering for annealed and as-cast polycrystals, respectively, to a disappearance of any type of magnetic ordering for single crystals. A close relationship between the magnetic ordering and the structural disorder in the Al layers isolated from the Ce–Pd layers is demonstrated. The exchange coupling via the Al layers along the c -axis, which leads to the AF ground state, critically depends on the occupation and distribution of Al atoms as proposed by Mentink et al . It is pointed out that the randomness remaining inevitably in the Al layers masks the intrinsic magnetic excitation in the AF ordered state.
11 citations
TL;DR: In this article, the orientation dependence of the Zeeman split quadrupole resonance frequencies has been measured at 4.2°K and the components of the field gradient tensor determined, and it is concluded that PrCl3 remains paramagnetic down to 1.7°K.
Abstract: The 35Cl and 37Cl pure quadrupole resonances have been observed in PrCl3. At 4.2°K the frequencies are 4.5667±0.0001 and 3.6001±0.0001 Mc/sec for 35Cl and 37Cl, respectively, and at 77°K they are correspondingly 4.5607±0.0001 and 3.5955±0.0002 Mc/sec. The orientation dependence of the Zeeman split quadrupole resonance frequencies has been measured at 4.2°K and the components of the field gradient tensor determined. The asymmetry parameter η is 0.58±0.02. No evidence of a transition to an ordered state was observed, and it is concluded that PrCl3 remains paramagnetic down to 1.7°K. A shift in the Zeeman frequencies with temperature was found and is attributed to the hyperfine interaction of the Cl nuclei with the Pr electronic ground state. The results are compared with the results of a calculation of the field gradient from a point charge model, and are also discussed in terms of covalent bonding.
11 citations
TL;DR: In this paper, the Zeeman effect of the 81Br and 35Cl nuclear quadrupole resonance on single crystals of para-bromophenol and para-chlorophenol was studied with high precision.
Abstract: The Zeeman effect of the 81Br and 35Cl nuclear quadrupole resonance has been studied with high precision on single crystals of para‐bromophenol and para‐chlorophenol, respectively. The results substantially agree with previous x‐ray and NQR studies of para‐chlorophenol (x‐ray studies are known only for this substance). In p‐bromophenol, four physically inequivalent sites were found, instead of two, as reported by other authors. Values of the asymmetry parameter are, respectively, ηBr = 0.0534 ± 0.001, ηCl = 0.071 ± 0.001 (34.12 MHz), and ηCl = 0.096 ± 0.001 (34.35 MHz).
11 citations