Knight Shift Tensor Research Articles

NMR studies on antiferromagnetic fluctuation in [formula omitted

We have carried out 195Pt-NMR measurements on a heavy Fermion superconductor UPt3 at H∼1.5−2.0T to investigate the in-plane anisotropy in the normal state. For an applied field parallel to [112¯0] direction, split 195NMR line are observed, which has not been reported previously. Such a line splitting is explained by anisotropic Knight shift tensors associated with the local symmetry of Pt-site in UPt3.

Magnetic excitation and local magnetic susceptibility of the excitonic insulator Ta2NiSe5 investigated by Se77 NMR

$^{77}\mathrm{Se}$ NMR measurements were made on polycrystalline and single-crystalline samples to elucidate local magnetic susceptibility and magnetic excitation of ${\mathrm{Ta}}_{2}{\mathrm{NiSe}}_{5}$, which is proposed to undergo an exciton condensation accompanied by a structural transition at ${T}_{\mathrm{c}}=328\phantom{\rule{0.16em}{0ex}}\mathrm{K}$. We determine the $^{77}\mathrm{Se}$ Knight shift tensors for the three Se sites and analyze their anisotropy based on the site symmetry. The temperature dependence of the Knight shift is discussed on the basis of spin and orbital susceptibilities calculated for two-chain and two-dimensional three-band models. The large fraction of the Se $4p$ orbital polarization due to the mixing between Ni $3d$ and Se $4p$ orbitals is estimated from the analysis of the transferred hyperfine coupling constant. Also the nuclear spin-lattice relaxation rate $1/{T}_{1}$ is found not to show a coherent peak just below ${T}_{\mathrm{c}}$ and to obey the thermally activated temperature dependence with a spin gap energy of $1770\ifmmode\pm\else\textpm\fi{}40\phantom{\rule{0.16em}{0ex}}\mathrm{K}$. This behavior of $1/{T}_{1}$ monitors the exciton condensation as proposed by the theoretical study of $1/{T}_{1}$ based on the three-chain Hubbard model for the excitonic insulator.

Measurements of the NMR Knight shift tensor and nonlinear magnetization in URu2Si2

URu$_2$Si$_2$ exhibits an anomalous peak in the nonlinear magnetic susceptibility at the hidden order transition. In order to investigate this anomaly, we conducted direct magnetization measurements and investigated the detailed angular dependence of the $^{29}$Si nuclear magnetic resonance Knight shift tensor. We find that the nonlinear magnetization is smaller than previously reported, and the analogous nonlinear Knight shift tensor is below the detection limit. Our results suggest that the magnitude of the anomalous peak is sample dependent.

Sb-NMR/NQR studies of heavy fermion system YbRhSb

We report a study of 121Sb nuclear magnetic resonance (NMR) and nuclear quadrupole resonance (NQR) in a Yb-based heavy fermion system YbRhSb using a single crystal. Sharp 121Sb-NMR lines were observed for each crystal axis for B‖a,b,c. From comparison with observed Sb-NMR spectra and numerical simulations, electric field gradient (EFG) parameters and Knight shift parameters are obtained at 10 K. The obtained quadrupole frequency, asymmetry parameter, isotropic Knight shift and anisotropic principal values of Knight shift tensors are νQ = 18.8 MHz, , and , respectively. We also succeeded in observing 121Sb-NQR signals at around 19.5 and 37 MHz, which are reproduced by the nuclear quadrupole Hamiltonian with νQ = 18.8 MHz and η = 0.2. We mention the relation between the anisotropy of the Knight shift and magnetic susceptibility. Our NMR/NQR results suggest that the weak ferromagnetism in YbRhSb is ascribed to a canted antiferromagnetic state.

Solid state 27Al NMR investigation of Knight shift tensors of LnAl2 (Ln=Y, La and Lu) and correlation with DFT calculations

The atomic and electronic structures of LnAl2 (Ln=Y, La and Lu) on Al sites were characterized by 27Al solid state NMR spectroscopy. 27Al isotropic metallic shifts have been determined in these cubic laves phases under both static and magic angle spinning (MAS) conditions. Based on band structure calculations, we found a strong correlation of 27Al isotropic metallic shifts and s character of the density of states at the Fermi level on Al sites. We also found tetrahedral distortion of Al centered clusters, which can be well characterized by quadruple coupling constants and Knight shift anisotropy.

Local spin susceptibility in the orbital-frustrated vanadium oxide BaV10O15

BaV10O15 having a bilayer triangular lattice exhibits a semiconductor-insulator transition accompanied by the structural phase transition at Tc ∼130 K. We show the microscopic properties of the phase transition investigated by 51V NMR measurements on a single crystal. We have observed 51V NMR spectra from two of the three inequivalent V sites at high temperatures. The Knight shift tensors are determined at 300 K for the two V sites. The local spin susceptibility strongly depends on the V sites and temperature despite the nearly independent magnetic susceptibility. Each spectrum is split into two below 200 K far above Tc, suggesting a charge/order ordering transition. The local spin susceptibilities of the three sites gradually vanish with decreasing temperature, consistent with the V trimer formation. The microscopic evidence for the spin singlet state is clearly observed below Tc.

Rotation of hyperfine fields at the V site in the multiband metal K2V8O6

51V nuclear magnetic resonance measurements are conducted on a single crystal of the mixed valence compound K2V8016 with 1.25 3d electrons per one V site. We determine the 51V Knight shift tensor, 51K, in the metallic state. 51K has the small anisotropy despite the conduction electrons in the anisotropic 3d orbitals. The principal axis of 51K rotates continuously on cooling temperature in the metallic state without breaking the lattice symmetry, I4/m. Taking into account the isotropic spin susceptibility, the thermal variation is attributed to a change in the hyperfine field tensor reflecting the 3d orbital shape.

15N NMR studies of layered nitride superconductor LixZrNCl

NMR measurements were carried out on pristine ZrNCl and LixZrNCl. From the 15N-Knight shift study, the isotropic Knight shift, the traceless chemical (orbital) shift tensor and the traceless Knight shift tensor were determined as Kiso=−71ppm, (σ1, σ2, σ3)=(−55, −55, 110)ppm and (K1, K2, K3)=(48, 48, −96)ppm, respectively. In the superconducting state, the fractional change of the 15N NMR shift for H∥ab was observed, evidencing that the pairing symmetry is a spin-singlet state.

Formula omitted] and [formula omitted] MAS NMR and magnetic characterization of [formula omitted

11 B and 89 Y MAS NMR spectra at room temperature and magnetization in the temperature range (2–300 K) were measured on a powder specimen of Y B 4. The three different 11 B Knight shifts (34.7, 12.6 and 5.4 ppm) for the crystallographic sites B1(4e), B2(4h) and B3(8j), respectively, were observed in a magnetic field of 17.6 T. The 89 Y isotropic Knight shift (294.6 ppm) and K x x , K y y and K z z components of the Knight shift tensor have been determined. The spin–lattice relaxation times, T 1 ( 11 B ) = 4.5 s and T 1 ( 89 Y ) = 5.5 s , were measured at room temperature. Analysis of the magnetization data have indicated that Y B 4 is a diamagnetic compound with the temperature independent component of its magnetic susceptibility equal to − 5.9 ∗ 1 0 − 9 ( m 3 / kg ) . Some of these data were referred to those of CaB 4 − x C x ( x = 0.21 ) , LaB 4 , NdB 4 and Y 5 Si 2 B 8 .

Analysis of 11B NMR Powder Lineshape of MgB2 in the Normal Conductive Phase

11 B nuclear magnetic resonance (NMR) measurements have been performed on MgB 2 powder sample at several magnetic fields ranging from 6.3 to 21.9 T. The isotropic Knight-shift, as well as quadrupole coupling frequency, was accurately determined from magic-angle spinning (MAS) spectra by analyzing its magnetic-field dependence. These NMR parameters were then used to interpret its static powder-pattern spectra observed at various magnetic fields, which reflect both the anisotropic Knight-shift tensor and the second-order quadrupole coupling tensor. We found that the Knight-shift tensor and the quadrupole coupling are both axially symmetric and their relative orientation to the molecular frame was also determined. This is the first experimental determination of the anisotropy of the Knight-shift of MgB 2 in a powder form from an exact analysis of the powder lineshape of the 11 B NMR spectra. The anisotropy was found to be very small (∼4 ppm), being in consistent with previous observations indicating that ani...

Hyperfine Interactions in the Heavy-Fermion Superconductor UBe13: 9Be NMR Studies

9 Be NMR measurements have been performed for a single crystal UBe 13 with T c ≈0.86 K. For an applied field parallel to [001] direction, we observed a well-split 9 Be NMR line with the sharp line-width of ≈10 Oe, guaranteeing the high-quality of the single crystal from the microscopic viewpoint. We also calculated the electric field gradient ( 9 EFG) tensor at Be(II) site using the band-structure calculation based on an FLAPW-LDA method. From the field-angle dependence of 9 Be-NMR spectra together with the result of the band-structure calculation, we identified the 9 EFG and 9 Be Knight shift tensors. The Knight shift of UBe 13 is enhanced by a factor of hundreds compared to that of a pure Be metal, suggesting the local spin density at Be 2 s and 2 p orbitals is enhanced through the hybridization with 5 f electrons. The isotropic and anisotropic hyperfine fields are obtained as A iso ≈436 Oe/µ B , ( A s 1 , A s 2 , A s 3 )≈(192,44,-236) Oe/µ B . The anisotropic part can be explained by the spin-dipolar f...

Fabrication of Magnetic Spider Silk and Other Silk-Fiber Composites Using Inorganic Nanoparticles

C NMR study of the organic superconductor k-(ET)2Cu[N(CS)2]Br via MAS and cross-polarization techniques with C-enriched ET molecules. The Knight shift tensor of the central carbon atoms has been derived. A lowering of the symmetry below 273 K has been deduced from the splitting of the C MAS NMR lines of the central carbons. A distortion of the organic lattice occurs below about 200 K when the motion of the ethylene groups is frozen. The incommensurate character of the distortion is implied by the inhomogeneous broadening of the NMR lines. This feature rules out the commensurate nature claimed from earlier diffuse X-ray scattering experiments.

NMR study of trialuminide intermetallics

We present a systematic study of the ${\mathrm{DO}}_{22}$-structure trialuminide intermetallic alloys using ${}^{27}\mathrm{Al}$ NMR spectroscopy. The quadrupole splittings, Knight shifts, and spin-lattice relaxation times on ${\mathrm{Al}}_{3}\mathrm{Ti}$, ${\mathrm{Al}}_{3}\mathrm{V}$, ${\mathrm{Al}}_{3}\mathrm{Nb}$, and ${\mathrm{Al}}_{3}\mathrm{Ta}$ have been identified. Knight-shift tensors were isolated by observation of quadrupole satellite lines and fitting to the central-transition powder patterns. The results are associated with the local electronic density of states for each crystallographic site. Universally small isotropic Knight shifts and long ${T}_{1}$'s are consistent with low Fermi-surface densities of states indicating the importance of Fermi-surface features for the phase stability of these alloys. Larger anisotropic Knight shifts occurring at aluminum site I indicate strong hybridization at this site, and the electric-field-gradient tensors confirm the strong $\mathrm{ab}$ plane bonding configuration. Local-moment magnetism is found in ${\mathrm{Al}}_{3}\mathrm{V}$, yet electrically this material appears very similar to the other ${\mathrm{DO}}_{22}$ aluminides.

Determination of the spin density distribution in the organic conductor DMTM(TCNQ)2 with 13C magic angle spinning NMR

13C magic angle spinning (MAS) NMR experiments on the organic conductor N,N-dimethylthiomorpholinium bis-tetracyanoquino-dimethane [DMTM(TCNQ)2]isotopically enriched at the position of the C-2 carbons of TCNQ are reported. Two isotropic resonances are resolved above the structural phase transition at 272 K, both exhibiting large positive isotropic and anisotropic Knight shifts. Sideband analysis of the MAS spectra has yielded the complete Knight shift tensors above T c, in the insulating state. From the Knight shifts the hyperfine couplings and spin densities at the C-2 sites were calculated and were found to be in good agreement with molecular calculations. Below T c, the sideband pattern displays two sets of 13C-2 lines indicating a spin density distribution between two sites of 0·59 :0·41.

Determination of the spin density distribution in the organic conductor DMTM(TCNQ)2 with 13C magic angle spinning NMR

13C magic angle spinning (MAS) NMR experiments on the organic conductor N,N-dimethylthiomorpholinium bis-tetracyanoquino-dimethane [DMTM(TCNQ)2]isotopically enriched at the position of the C-2 carbons of TCNQ are reported. Two isotropic resonances are resolved above the structural phase transition at 272 K, both exhibiting large positive isotropic and anisotropic Knight shifts. Sideband analysis of the MAS spectra has yielded the complete Knight shift tensors above T c, in the insulating state. From the Knight shifts the hyperfine couplings and spin densities at the C-2 sites were calculated and were found to be in good agreement with molecular calculations. Below T c, the sideband pattern displays two sets of 13C-2 lines indicating a spin density distribution between two sites of 0·59 :0·41.

Knight shift, electric-field gradient, and electronic state in the spin-Peierls compound CuGeO3: 63,65Cu NMR in a single crystal.

$^{63,65}\mathrm{Cu}$ NMR measurements have been performed to study Knight shift and electric-field gradient (EFG) tensors in the spin-Peierls (SP) compound ${\mathrm{CuGeO}}_{3}$, which undergoes the SP transition at ${\mathit{T}}_{\mathrm{SP}}$\ensuremath{\sim}14 K, using a single crystal. From the numerical analysis of the $^{63,65}\mathrm{Cu}$ NMR spectra based on a nuclear Hamiltonian including Zeeman and electric quadrupole interactions, we have precisely determined the principal values and axes of the Knight shift and EFG tensors. Based on theses results, the orbital susceptibility and hyperfine interaction are discussed within a ${\mathrm{Cu}}^{2+}$ single-ion model in a rhombic crystal field. Consequently, the crystal field parameters are obtained. \textcopyright{}1996 The American Physical Society.

An 17O NMR study of Hg 0.5Tl 0.5Ba 2(Ca 1−xSr x) 2Cu 3O 8+δ

We have obtained 17O nuclear magnetic resonance spectra of magnetically aligned Hg 0.5Tl 0.5Ba 2(Ca 1−xSr x) 2Cu 3 O 8+δ at 300 K. The principal components of the electric-field gradient and the Knight-shift tensors are obtained for all oxygen sites in this mercury-based triple Cu-O layered superconductor. The results show that both the EFG and Knight shift tensors of the inner CuO 2 plane oxygens are considerably smaller than those of the outer CuO 2 plane oxygens, indicating a smaller spin susceptibility and a reduced hole density in the inner CuO 2 plane.

Single-spin fluid, spin gap, and d-wave pairing in YBa2Cu4O8: A NMR and NQR study.

We present results of $^{17}\mathrm{O}$ and $^{63,65}\mathrm{Cu}$ nuclear magnetic resonance (NMR) and nuclear quadrupolar resonance (NQR) studies in the normal and superconducting state of the 82-K superconductor ${\mathrm{YBa}}_{2}$${\mathrm{Cu}}_{4}$${\mathrm{O}}_{8}$. The various components of the Cu and O Knight-shift tensors show strong but similar temperature dependences over the temperature range from 8.5 to 300 K in both the ${\mathrm{CuO}}_{2}$ planes and the chains, supporting the picture that there is only one spin component in the planes and the chains, although with different susceptibilities. The oxygen data obey the Korringa relation. This may be interpreted as Fermi-liquid behavior of the electronic system far away from the antiferromagnetic wave vector. The temperature dependence of both the planar Cu and O shift tensors and the planar Cu spin-lattice relaxation rate suggest the opening of a pseudo-spin-gap well above ${\mathit{T}}_{\mathit{c}}$. The very different temperature dependence of 1/${\mathit{T}}_{1}$ at the planar O and Cu sites points to the reduced role of the antiferromagnetic correlated spin fluctuations at the O site. The data favor the conclusion that ${\mathrm{YBa}}_{2}$${\mathrm{Cu}}_{4}$${\mathrm{O}}_{8}$ is a d-wave superconductor. Evidence is provided by three data sets: the chain Knight shifts, the ratio of the planar copper and oxygen relaxation rates, and the individual low-temperature behavior of these rates.

NMR properties of hcp Ru metal — first detection of the99Ru and101Ru NMR in a paramagnetic solid

Results of nuclear magnetic resonance (NMR) measurements on hexagonal close-packed Rumetal are presented. The field spectra of both isotopes, having a nuclear spinI of 5/2, show a shape characteristic for quadrupolar disturbed NMR. From a simulation of these spectra, the electric field gradientVzz has been determined to be (37±0.5)×10−13 esu/cm3 in agreement with recent band structure calculations. The Knight shift tensor elements deduced from the spectra areKx=Ky=0.46±0.02% andKz=0.56±0.02%. These rather high and positive shifts are completely in line with that of the neighboring elements in the periodic system and have primarily to be ascribed to the Van Vleck contribution. This part of the Knight shift is also responsible for the rather strong anisotropy, that has been found.

Nuclear magnetic resonance line shape of 139La in non-stoichiometric lanthanum hydrides at low temperatures

The 139La nuclear magnetic resonance of lanthanum hydrides in LaH 2+ x ( x = 0.32, 0.38, 0.40, 0.74) was measured over the temperature range 2.3 to 303 K. A single, temperature-dependent line width was found in LaH 2.74 above 250 K, whereas a complex spectrum was observed at lower temperatures. The low temperature line shape can be described as the superposition of two resonances with the same intensity but different electric field gradients and Knight shift tensors. They were correlated with two lanthanum sites in the LaH 2.75 superlattice proposed on the basis of neutron diffraction and specific heat measurements. For the LaH 2.32-LaH 2.40 samples, the spectrum can also be decomposed into two resonances. However, in this case, one line can be attributed to the LaH 2.5 superlattice and the origin of the second line is briefly discussed.