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.

Application of Nuclear Quadrupole Resonance with Mini Cubic Anvil Apparatus

Abstract: A wide variety of experimental methods under high pressure are now applied to various materials. For nuclear magnetic resonance (NMR) and nuclear quadrupole resonance (NQR) methods, high pressure measurements up to about 3.5GPa are performed conventionally because of the development of hybrid cylinder clamp cells. In this pressure range, we have examined the suitable pressure transmitting media, which can give more hydrostatic pressure to sample, by comparing the Cu-NQR spectral width of Cu2O and its pressure efficiency between room temperature and 4.2K. Further high pressures for the NMR/NQR methods can be achieved by an indenter-type clamp cell (up to about 5GPa), a modified Bridgman anvil cell (up to about 10GPa), and so on. However, these higher pressure measurements are not general at present stage because of their smaller sample space than that of the piston cylinder cell. Typically the diameter and the height of the sample space is ’ 1:7mm and h ’ 1:4mm for the indenter-type clamp cell and ’ 1:0mm and h ’ 1:0mm for the modified Bridgman anvil cell, while that for the piston cylinder cell is ’ 4:0mm and h ’ 20mm or larger. Moreover, it is quite difficult to obtain hydrostatic pressure above about 5GPa. This is because the pressure by the Bridgman anvil at higher pressures has a tendency of uniaxial stress to sample space. Cubic anvil apparatus has an advantage in this point since the cubic anvil apparatus can induce pressure nearly isotropically to sample space. It can also achieve high pressure up to about 20GPa. The line width of Cu-NQR of Cu2O is a good measure of pressure homogeneity since the pressure homogeneity inside pressure cell is strongly related to the broadening of NMR/NQR spectra. Hence, we performed Cu-NQR measurements of Cu2O up to about 7.5GPa with mini cubic anvil apparatus in order to obtain more hydrostatic pressure under 10GPa-class high pressure. Note that the sample space itself is comparable to that of the indenter-type cell and about four times larger than that of the modified Bridgman anvil cell; ’ 2:0mm diameter and h ’ 1:0mm height. This larger sample enables us to obtain strong enough intensity even at room temperature. To the best of our knowledge, this is the first report on the NMR/NQR measurement with the use of the cubic anvil apparatus. The Cu-NQR measurements of Cu2O were performed using a phase-coherent pulsed NQR spectrometer in the resonance frequency range 26–29MHz. We used Cu2O powder (99.9%) and glycerin mixed with the ratio of 20 : 1. Inside the sample coil, this mixture was set up. We consider that a small amount of the glycerin does not behave as pressure transmitting medium. We performed the NQR measurements at room temperature (about 300K). The obtained spin echo data were Fourier transformed to NQR spectra. Below about 3GPa, the line shape at a pressure was obtained at an excitation resonance frequency because the line shape was narrow enough to detect by measuring NQR pulse width. We used mini cubic anvil apparatus (Fig. 1) which is recently developed by Takeshita et al. We use nonmagnetic WC anvil top at present stage, but we can change other nonmagnetic and insulating anvil tops. Its overall volume including of cryostat is about 30 times smaller than that of conventional cubic anvil apparatus for low temperature measurements. Furthermore, the weight of its guide block is approximately 3 kg, which is about 7 times lighter than that of conventional one. However, its sample space is the same as that of the conventional one. The present maximum pressure of this apparatus is about 10GPa with the use of MgO gasket, but we used pyrophyllite gasket in this study, with which the maximum pressure of the apparatus is about 7.5GPa, in order to ensure reproducibility. Single-layer coil wound about 20 turns was used in our measurements ( 1⁄4 1:5mm, h 1⁄4 0:7mm). We used a 1 : 1 mixture of Fluorinert 70 and 77 (Fluorinert). In our previous Cu-NQR measurements of Cu2O with hybrid piston cylinder cell, the pressure homogeneity using Fluorinert medium was the worst among the available pressure media above 1GPa. We also used Fluorinert with the modified Bridgman anvil cell where the large pressure inhomogeneity exists. In this study, we examine the pressure homogeneity of the mini cubic anvil apparatus and compare the pressure homogeneity with various apparatus using the same pressure transmitting medium. We may expect the drastic improvement of the homogeneity with the cubic anvil apparatus even using the Fluorinert. Fig. 1. (Color online) A mini cubic apparatus and its guide block on the palm.

Nuclear Quadrupole Resonance of N 14 in Ethylenediamine

Abstract: The temperature dependence of the nuclear quadrupole resonance of N 14 in C 2 H 4 (NH 2 ) 2 was studied between 77°K and 280°K. The resonance lines were measured with a Pound-Watkins' type recording spectrometer by applying frequency modulation. The curve of resonance frequency vs. temperature exhibited a break around 180°K. It could be attributed to a phase transition of the crystal structure. Another break suggesting the phase transition was also observed around the liquid nitrogen temperature. The quadrupole coupling constant eQq and the asymmetry parameter η were 3.9965 Mc and 0.313 at the liquid nitrogen temperature. By assuming hybridized atomic orbitals of sp 3 type for the nitrogen bonds, two alternative models were employed. In one model three nitrogen bonds have equal s-hybridization, and in the other model s-hybridization of the N-C bond is different from that of the N-H bonds. It was shown that the latter model was suitable.

Simple Bridge for Pulsed Nuclear Magnetic Resonance

Abstract: An asymmetrical rf bridge for pulsed magnetic resonance experiments is described. The balancing adjustments, which can be made quickly and easily, ensure a proper impedance match to transmitter and receiver. The bridge is particularly well suited for pure nuclear quadrupole resonance experiments.

Nuclear magnetic resonance in the antiferromagnetic heavy-fermion system UCu5: spin reorientation at 1 K

Abstract: The magnetic properties of UCu5 with the C15b-type cubic crystal structure, which shows an antiferromagnetic transition at 15 K and, further, an unidentified transition at 1 K, were investigated by using the nuclear magnetic resonance (NMR) and nuclear quadrupole resonance (NQR) techniques. The measurements were performed for both crystallographically inequivalent Cu sites with cubic and trigonal symmetry in all the paramagnetic, antiferromagnetic and unidentified states. The results clearly indicate that the low-temperature state below I K is another antiferromagnetic state with a different spin structure from the high-temperature state. From the temperature variation of the field-swept spectrum, we propose a non-collinear quadruple-q (4-q) structure for the state between 15 and 1 K, which is different from the structure previously proposed by Murasik et al based on their neutron diffraction result. Furthermore, we propose a collinear single-q (1-q) structure for the state below 1 K, which cannot be distinguished from the 4-q structure by neutron diffraction. Assuming a simple model for hyperfine interactions and the magnetic structures, we consistently explain the complicated zero-field spectra obtained both above and below 1 K. The analysis shows clearly the spin reorientation at 1 K and that the variation of the local field at Cu sites is reasonably interpreted in terms of only the spin reorientation. The analysis also indicates that the electric field gradient changes significantly at 1 K, which is in contrast to no change at 15 K. The relation between the spin reorientation and the gap formation at 1 K is discussed.

Applications of adiabatic half passage to NQR

Abstract: The application of nuclear quadrupole resonance (NQR) to the detection of materials can be hampered by the low sensitivity of the technique. The use of surface coils for remote detection only exacerbates this problem. In this paper we demonstrate the advantages of adiabatic half passage (AHP) for NQR detection ofI=1 spins in powder samples. Under optimal conditions, AHP provides a 15% sensitivity enhancement over traditional optimized, pulsed excitation. AHP excitation is independent of ω1 over more than an order of magnitude variation in radio-frequency (rf) field strength, and can provide up to a factor of two or more sensitivity enhancement over traditional pulsed excitation in inhomogeneous rf magnetic fields. In pulsed spin-locking-type experiments, AHP as a prepulse can provide near constant signal amplitude over a factor of two variation in rf magnetic field strength.