Temperature Dependence Of Knight Shift Research Articles

Intrinsic Spin Susceptibility and Pseudogaplike Behavior in Infinite-Layer LaNiO_{2}.

The recent discovery of superconductivity in doped infinite-layer nickelates has stimulated intensive interest, especially for similarities and differences compared to that in cuprate superconductors. In contrast to cuprates, although earlier magnetization measurement reveals a Curie-Weiss-like behavior in undoped infinite-layer nickelates, there is no magnetic ordering observed by elastic neutron scattering down to liquid helium temperature. Until now, the nature of the magnetic ground state in undoped infinite-layer nickelates was still elusive. Here, we perform a nuclear magnetic resonance (NMR) experiment through ^{139}La nuclei to study the intrinsic spin susceptibility of infinite-layer LaNiO_{2}. First, the signature for magnetic ordering or freezing is absent in the ^{139}La NMR spectrum down to 0.24K, which unambiguously confirms a paramagnetic ground state in LaNiO_{2}. Second, a pseudogaplike behavior instead of Curie-Weiss-like behavior is observed in both the temperature-dependent Knight shift and nuclear spin-lattice relaxation rate (1/T_{1}), which is widely observed in both underdoped cuprates and iron-based superconductors. Furthermore, the scaling behavior between the Knight shift and 1/T_{1}T has also been discussed. Finally, the present results imply a considerable exchange interaction in infinite-layer nickelates, which sets a strong constraint for the proposed theoretical models.

Momentum-resolved superconducting energy gaps of Sr2RuO4 from quasiparticle interference imaging

Sr2RuO4 has long been the focus of intense research interest because of conjectures that it is a correlated topological superconductor. It is the momentum space (k-space) structure of the superconducting energy gap [Formula: see text] on each band i that encodes its unknown superconducting order parameter. However, because the energy scales are so low, it has never been possible to directly measure the [Formula: see text] of Sr2RuO4 Here, we implement Bogoliubov quasiparticle interference (BQPI) imaging, a technique capable of high-precision measurement of multiband [Formula: see text] At T = 90 mK, we visualize a set of Bogoliubov scattering interference wavevectors [Formula: see text] consistent with eight gap nodes/minima that are all closely aligned to the [Formula: see text] crystal lattice directions on both the α and β bands. Taking these observations in combination with other very recent advances in directional thermal conductivity [E. Hassinger et al., Phys. Rev. X 7, 011032 (2017)], temperature-dependent Knight shift [A. Pustogow et al., Nature 574, 72-75 (2019)], time-reversal symmetry conservation [S. Kashiwaya et al., Phys. Rev B, 100, 094530 (2019)], and theory [A. T. Rømer et al., Phys. Rev. Lett. 123, 247001 (2019); H. S. Roising, T. Scaffidi, F. Flicker, G. F. Lange, S. H. Simon, Phys. Rev. Res. 1, 033108 (2019); and O. Gingras, R. Nourafkan, A. S. Tremblay, M. Côté, Phys. Rev. Lett. 123, 217005 (2019)], the BQPI signature of Sr2RuO4 appears most consistent with [Formula: see text] having [Formula: see text] [Formula: see text] symmetry.

Ferromagnetic spin fluctuations in the filled skutterudite SrFe4As12 revealed by As75 NMR-NQR measurements

$^{75}$As nuclear magnetic resonance (NMR) and nuclear quadrupole resonance (NQR) measurements have been carried out to investigate the magnetic and electronic properties of the filled skutterudite metallic compound SrFe$_4$As$_{12}$. The temperature dependence of Knight shift $K$ determined by the NQR spectrum under a small magnetic field ($\le$ 0.5 T) shows the similar temperature dependence of the magnetic susceptibility $\chi$ which exhibits a broad maximum at $T^\ast$ $\sim$ 50 K. The nuclear spin-lattice relaxation rate divided by temperature, 1/$T_1T$, increases with decreasing temperature and exhibits a broad maximum at $T$ $\sim$ 70 K, similar to the case of $\chi$. The temperature dependence of $K$ and $1/T_1T$ is reasonably explained by a simple model where we assume a concave-shaped band structure near the Fermi energy. Based on a Korringa ratio analysis using the $T_1$ and $K$ data, ferromagnetic spin fluctuations are found to exist in SrFe$_4$As$_{12}$. These results indicate that SrFe$_4$As$_{12}$ can be characterized to be a metal with ferromagnetic correlations and also the peculiar band structure responsible for the suppression of $1/T_1T$ and $K$ at low temperatures.

NMR spectrum analysis for CrAs at ambient pressure

We report NMR spectrum analysis for CrAs, which was recently reported to be superconducting under pressure. The NMR spectrum obtained by the powdered single crystals shows a typical powder pattern reproduced by the electric field gradient (EFG) parameters and isotropic Knight shift, indicating anisotropy of Knight shift is not remarkable in CrAs. For the oriented sample, the spectrum can be understood by considering that the crystals are aligned for H∥b. The temperature dependence of Knight shift was successfully obtained from NMR spectrum with large nuclear quadrupole interaction.

Finite-size effects in the nuclear magnetic resonance of epitaxial palladium thin films

We have measured the NMR of ${}^{8}$Li${}^{+}$ implanted in a set of thin epitaxial films of Pd. We find a large, negative, strongly temperature-dependent Knight shift $K$ consistent with previous measurements on polycrystalline films. The temperature dependence of the shift exhibits a characteristic deviation from the susceptibility $\ensuremath{\chi}(T)$. In particular, at low temperature, $K(T)$ continues to follow a simple Curie-Weiss dependence. This result provides important insight into the origin of the low-temperature behavior of $\ensuremath{\chi}(T)$ in strongly paramagnetic metals. In addition, we find the room temperature shift depends on film thickness, with changes on the order of 20% between films 100 nm and 30 nm thick. We also observe a surface-related resonance in both Au-capped and uncapped films with a small positive shift. These features bear a striking similarity to the Pt NMR line shapes in much smaller Pt particles. However, they seem to originate, not from adsorbed species, but rather in confinement effects on the highly exhange-enhanced Pd $d$ band.

T-dependent Nuclear Hyperfine Coupling at the In Site in CeIrIn5

Temperature dependence of Knight shift K at 115 In sites in heavy fermion superconductor CeIrIn 5 has been determined for applied magnetic field parallel to a - and c -axes. The Knight shift versus the static susceptibility χ: ( K -χ) plot is non-linear at low temperatures in this compound, indicating that the hyperfine coupling constant depends on temperature. The T -dependence of hyperfine coupling constant is related with the modification of electronic state due to a heavy fermion formation. The non-linear relation between K and χ is discussed.

27Al and 63Cu NMR studies on intermetallic Kondo compound CeCu 3Al 2

Detailed 27Al and 63Cu nuclear magnetic resonance (NMR) experiments have been performed in between 4.5 and 295 K on a polycrystalline sample of CeCu 3Al 2 which has a Kondo temperature ∼ 11 K . The NMR spectral features and Knight shift measurements show that in this compound, Cu occupy both c and g lattice sites, while Al occupy only the g sites. From the temperature dependence of Knight shift ( K), the hyperfine fields for 63Cu and 27Al at the g sites have been estimated as 2.02(5) and 1.67 ( 5 ) kOe / μ B , respectively, and that for 63Cu at c sites as − 3.83 ( 5 ) kOe / μ B . Nuclear spin-lattice relaxation time ( T 1) measurements indicate that though the relaxation process is governed by fluctuations of magnetic interaction, nuclear quadrupolar interaction also has a significant contribution, especially towards relaxation of 63Cu in both c and g sites. For 27Al, K and T 1 have yielded the effective 4f-spin correlation rate 1 / τ 4 f . The behavior of its temperature dependence indicates that at low temperatures in CeCu 3Al 2, the valence state of cerium might not be stable.

Spectroscopic Study of75As and139La NMR on Layered Structure Ferromagnet LaCoAsO

75 As and 139 La field-swept NMR spectra were obtained for the novel weakly itinerant ferromagnet LaCoAsO with a two-dimensional layered structure above the Curie temperature of 55 K. By analyzing NMR spectra, temperature dependences of Knight shift K and nuclear quadrupole resonance frequency ν Q were obtained successfully for each nucleus. We confirmed from the so-called K –χ plots that the macroscopic magnetization of our LaCoAsO powder sample is intrinsic and does not contain the contribution from impurity phases. We estimated hyperfine coupling constants from the slope of K –χ plots and compared them with that of an iron-arsenide superconductor.

Temperature dependence of Knight shifts for 12 B in Pt

The Knight shift of a short lived β-emitting nucleus 12B (I=1, T 1/2=20 ms) implanted into Pt has been measured as a function of temperature (140–600 K) by means of the β-NMR method. The relation between the Knight shift and the susceptibility for Pt was deduced, which shows the similar tendency to that for the case of 12B in Pd.

Electronic structure of theNa16Rb8Si136andK16Rb8Si136clathrates

We have calculated the electronic structure and the equations of state of the ${\mathrm{Na}}_{16}{\mathrm{Rb}}_{8}{\mathrm{Si}}_{136}$ and ${\mathrm{K}}_{16}{\mathrm{Rb}}_{8}{\mathrm{Si}}_{136}$ clathrates. These compounds are based on the type II silicon clathrate structure. The smaller Na (or K) atoms occupy the 20-atom cages, while the Rb atoms occupy the 28-atom cages. Equation of state, electronic band structure, and density of states calculations were performed using density functional theory in the local density approximation (LDA). The ``guest'' impurity atoms inside the cages modify the material electronic structure. Guest atom electrons occupy the ${\mathrm{Si}}_{136}$ conduction band states, resulting in a Fermi level shift into the conduction band of the ``parent'' ${\mathrm{Si}}_{136}$ framework. In qualitative agreement with the rigid-band model, the band structures display no major modifications due to the inclusion of the alkali metal guests. However, the electronic densities of states of the filled clathrates show two sharp peaks and a dip near the Fermi level. This feature may help to qualitatively explain the temperature-dependent Knight shift observed for the NMR-active nuclei in ${\mathrm{Na}}_{16}{\mathrm{Rb}}_{8}{\mathrm{Si}}_{136}$. We compare our calculations with experimental results for ${\mathrm{Na}}_{16}{\mathrm{Rb}}_{8}{\mathrm{Si}}_{136}$.

2D NMR study in the novel superconductor [formula omitted

We studied the 2D NMR spectrum on the novel superconductor Na 0.35 CoO 2 · 1.3 H 2 O . The temperature dependence of Knight shift at 2D in the normal state is parallel to that of magnetic susceptibility and the hyperfine coupling constant is estimated as 0.16 kOe / μ B . The resonance frequency in the low temperatures does not change below T c , which is contrast to that in 59Co site.

Phonon dispersion in the intermetallic compounds AuGa 2 and PtGa 2

The intermetallic compounds AuGa 2 and PtGa 2 have been studied extensively in recent years because of their rather surprising temperature dependent Knight shift and magnetic susceptibility. To gain some information on its vibrational properties, we have investigated the lattice dynamical properties of AuGa 2 and PtGa 2 by applying a modified rigid ion model. The phonon dispersion curves (PDCs) have been obtained for the principal symmetry directions. A comparison is made between the interatomic interactions and phonons of the two compounds. The calculated PDCs reveal that these compounds do not show any anomaly in their phonon properties. The calculated results are in good agreement with experiments.

Temperature-dependent hyperfine interactions in CePdAl

Nuclear magnetic resonance have been performed to study hyperfine interactions in CePdAl. The temperature dependence of Knight shift( K) and susceptibility( χ) is highly anisotropic as expected from its crystal structure. Non-linearity of K– χ plot was observed only when the magnetic field was perpendicular to c-axis. Two-dimensional short-range correlations are discussed.

Electronic structure of a 12:7 pyrene hexafluoroantimonate salt analyzed by solid state NMR

High-resolution 13C nuclear magnetic resonance (NMR) with 1H cross-polarization and 1H (gated) decoupling under magic angle spinning is measured for the quasi-one-dimensional organic conductor (Pyrene)12(SbF6)7 at temperatures between 170 and 270K. The spectra indicate that no neutral pyrene or solvent molecules are built-in to the crystal structure. The temperature-dependent Knight shift of two inequivalent carbon sites is analyzed.

17O NMR study on YBa 2Cu 4O 8

The temperature dependence of Knight shift 17 K in oriented polycrystalline samples of YBa 2Cu 4O 8 has been measured by the nuclear magnetic resonance (NMR) technique. From the detailed experiments, we obtained a remarkable result that both K ax and K aniso at the planar oxygen sites do not scale with K iso, while K iso scales with a uniform susceptibility. So far, while the single-spin freedom model has been believed from the scaling of these observables one another, this result claims that the single-spin freedom model should be reconsidered.

59CoNMR studies of metallicNaCo2O4

${}^{59}\mathrm{Co}$ NMR studies have been performed in metallic ${\mathrm{NaCo}}_{2}{\mathrm{O}}_{4}$ in the temperature range 350--100 K. The powder patterns predominantly correspond to typical second-order quadrupolar splitted central transition of two inequivalent cobalt sites. Features of magnetic interaction are also present. The analysis of the NMR line shape shows that the electric field gradient (EFG) experienced by one of the two sites (site 1) is independent of temperature, whereas around 47% increment in EFG has been observed for site 2 as the temperature is lowered from 350 to 100 K. ${}^{59}\mathrm{Co}$ NMR shift for each site is almost isotropic in character which varies linearly with susceptibility and basically consists of two parts. Both the sites suffer a large temperature independent shift due to the contribution from orbital paramagnetism $({\ensuremath{\chi}}_{\mathrm{vv}})$ which is analogous in metals to the Van Vleck paramagnetic susceptibility. The temperature-dependent Knight shift for site 1 reveals a negative hyperfine coupling constant ${(A}_{\mathrm{hf}}^{d})$ arising from inner s core polarization by the d electrons which are itinerant in character. A positive ${A}_{\mathrm{hf}}^{d}$ observed for site 2 cannot be interpreted directly in a metallic system such as ${\mathrm{NaCo}}_{2}{\mathrm{O}}_{4}.$ A comparison of the magnitude of ${A}_{\mathrm{hf}}^{d}$ with those of other cobalt oxides suggests that the nucleus which is being probed by NMR, belongs to a diamagnetic cobalt state. Thus the present NMR results together with the susceptibility indicate the presence of ${\mathrm{Co}}^{3+}$ ion with S = 0 and the magnetic ${\mathrm{Co}}^{4+}$ ion.

NMR evidence of BCS superconductivity in Y(Ni 1− xPt x) 2B 2C

13 C and 11 B NMR studies have been made on the quaternary superconductor Y(Ni 1− x Pt x ) 2B 2C with x=0 and 0.4. Temperature dependence of Knight shift and spin-lattice relaxation rate (SLRR) in the normal state was explained consistently among all the observed nuclei by Korringa mechanism without taking account of antiferromagnetic spin fluctuation. Bellow the superconducting transition temperature we observed a Hebel–Slichter peak in case of 13 C SLRR. These results mean that the borocarbide is a normal metal and a phonon-mediated superconductor

NMR studies of frustrated spin structure in UNi 4B

We have measured 11B NMR spectra in the hexagonal antiferromagnetic compound UNi 4B (Néel temperature T N = 20 K) over the temperature range 2–260 K. Spectra in the paramagnetic state yield a quadrupole splitting frequency of 0.215 ± 0.016 MHz and temperature-dependent Knight shifts. For applied field in the basal plane a Knight shift versus susceptibility plot yields a total hyperfine field of 1.14 ± 0.15 kOe/ μ B. The observed 11B line below T N in a c-axis field-oriented powder sample exhibits a partial powder pattern due to three magnetically inequivalent boron sites. The width of this line is consistent with the magnetic structure determined by neutron diffraction, using the transferred hyperfine field derived from paramagnetic-state 11B spectra, and therefore confirms the presence of the frustrated U spins.

Anomalous Knight Shift in CeP and CeAs

Anomalous temperature dependence of Knight shift with a peak structure including pressure effect in CeP and CeAs was studied based on the magnetic polaron model. It was shown that the simple crystal field model can induce a peak but cannot reproduce the whole temperature dependence consistently. On the other hand, the magnetic polaron model can reproduce the entire structure consistently including the pressure effect, in particular in CeP, but some problem remains in CeAs.

27Al nuclear magnetic resonance spectra in CeAl 3 at low temperature

We have measured the nuclear magnetic resonance, NMR, spectra of CeAl 3 at 3.964 MHz, 2.095 MHz and 0.937 MHz in the temperature range between 0.04 K and 20 K. The complicated NMR absorption line of CeAl 3 powder is shown to have more than one component, corresponding to at least two inequivalent Al sites. Below 0.9 K the relative intensity of a broad asymmetric structure increases, and the width of the NMR spectrum shows a rapid increase. At fields of the order of two kilogauss the asymmetry is strongly supressed. The temperature dependence of the asymmetry and width of the spectrum below 0.9 K, can neither be explained in terms of a temperature dependent Knight shift nor in terms of conventional magnetic ordering.