Magnetic Hyperfine Shift Research Articles

Magnetic structure of the square cupola compound Ba(TiO) Cu4(PO4)4

The magnetic structure of the antiferromagnetic square cupola compound Ba(TiO)Cu$_4$(PO$_4$)$_4$ with the tetragonal structure is studied with 31P nuclear magnetic resonance techniques. The magnetic hyperfine shift K shows a clear splitting at the N\'eel temperature T$_N$ = 9.5 K, where the resonance splits into two lines when an external magnetic field is oriented along the c axis and into four lines when the field is along the a axis. In the paramagnetic region K(T) follows temperature dependence of the magnetic susceptibility $\chi(T)$. From K vs $\chi$ plot we determined nearly isotropic hyperfine field values Ha_hf = 765 mT/$\mu_B$ and Hc_hf = 740 mT/$\mu_B$ for the magnetic field oriented along a and c, respectively. From the rotation of the single crystal in the external magnetic field we determined eight different orientations of K-tensor in the paramagnetic region. In the antiferromagnetic state at T = 6 K we found that the local field at phosphorus is mainly due to dipolar field of coppers. Here the rotation of the single crystal shows eight different orientations of the local field Bint = 35.6 mT. The orientations correspond to the calculation of dipolar fields at phosphorus assuming magnetic quadrupolar configuration of magnetic moments $\varGamma_3(1)$ described previously [Nat. Commun. 7, 13039 (2016); Phys. Rev. B 96, 214436 (2017)].

A Novel Ordered Phase in SrCu2(BO3)2 under High Pressure

We report results of 11 B NMR and susceptibility measurements on the quasi two-dimensional frustrated dimer spin system SrCu 2 (BO 3 ) 2 under high pressure. At 2.4 GPa and in a magnetic field of 7 T, NMR lines split with decreasing temperature in two steps. A gradual splitting below T = 30 K breaking the four-fold symmetry of magnetic response is followed by a further sudden splitting below 3.6 K. The latter indicates a magnetic phase transition, which is also marked by a kink in the susceptibility at 1.44 GPa. From the magnetic hyperfine shift data, we conclude that the low- T phase has a doubled unit cell containing two types of dimers, one in a nearly singlet state and the other with a finite magnetization down to T = 0.

Structural Transitions and Magnetic Structure in NH4CuCl3via14N-NMR

We report results of 14N-NMR experiments on NH4CuCl3 at the magnetic field of 7 T, where the 1/4-magnetization plateau is observed at low temperatures. The quadrupole coupling parameter νz splits below 70 K, indicating a structural phase transition. At 4.2 K, eight N sites with distinct values of both νz and the magnetic hyperfine shift Kz are resolved in the NMR spectrum for general field directions. We then conclude that the magnetic structure in the 1/4-plateau does not break the symmetry of the crystal. Based on the NMR and the recent neutron scattering results by Rüegg et al. [Phys. Rev. Lett. 93 (2004), 037207], we propose that triplet dimers in the 1/4-plateau are formed not between the nearest neighbor pairs but over different chains.

NMR study of antiferromagnetic black sodalite Na 8(AlSiO 4) 6

27 Al and 29 Si NMR spectra and spin–lattice relaxation in heavily sodium-doped sodalite Na 8(AlSiO 4) 6 are presented. The magnetic hyperfine shifts of 27 Al and 29 Si have Curie–Weiss-type temperature dependences with the same Weiss parameter Θ=−168±5 K. From an abrupt broadening of the resonance lines the transition temperature to the antiferromagnetic phase T N =54±2 K is determined. Above 200 K thermally activated ionic motion (activation energy, E A/ k B=2000 K) is found in sodalite cages containing Na 4 3+ ions which is much slower than the motion ( E A/ k B=750 K) in the cages containing Na 3 3+ ions.

63,65Cu NMR investigation ofCuGeO3ssingle crystals:mThe uniform and the dimerized spin-Peierls phase

We report a Cu NMR study performed under high magnetic field on single crystals of the inorganic spin-Peierls ${\mathrm{CuGeO}}_{3}$ compound, in its uniform and dimerized phases. The temperature (T) dependence of the magnetic hyperfine shift, i.e., the local static spin susceptibility, is found to scale the macroscopic susceptibility. This allows the determination of the hyperfine coupling tensor, which can be well accounted for by the on-site coupling associated with the localized electronic spin of a ${\mathrm{Cu}}^{++}$ ion in an approximately axially symmetric environment. The nuclear spin-lattice relaxation rate (${\mathrm{T}}_{1}^{\mathrm{\ensuremath{-}}1g}$) in the dimerized phase is found to be activated for temperature below \ensuremath{\sim}${\mathrm{T}}_{\mathrm{SP}}$ /2. The magnetic-field dependence of the activation energy is in good agreement with that of the energy gap determined by neutron inelastic scattering. In the uniform phase, neither the magnitude of ${\mathrm{T}}_{1}^{\mathrm{\ensuremath{-}}1g}$ (an order of magnitude smaller) nor its T dependence (approximately linear in T instead of being nearly constant) correspond to the theoretical predictions for a simple S=1/2, one-dimensional Heisenberg antiferromagnet, unless we admit for a filtering of the antiferromagnetic fluctuations, due to a small supertransferred hyperfine coupling. As expected, we found no magnetic-field dependence of ${\mathrm{T}}_{1}$ (T\ensuremath{\gtrsim}1.5 ${\mathrm{T}}_{\mathrm{SP}}$ ) in the range 8.9--14.9 T.

63Cu and 199Hg NMR in overdoped HgBa 2CaCu 2O 6+δ

We report on 63Cu and 199Hg NMR spectra and nuclear spin-lattice relaxation rate (1/ T 1) measurements, and the Cu NQR spectrum, in HgBa 2CaCu 2O 6+δ powder sample with T c = 101 K. The results agree with previous NMR studies in the overdoped regime of the cuprates, showing antiferromagnetic correlations and no spin-gap behaviour in the normal state. The Cu quadrupole coupling frequency 63 ν Q and orbital magnetic hyperfine shift 63 K orb c are relatively low, which might be connected to a strong in-plane CuO hybridization. The position of the 199Hg NMR spectrum is essentially determined by an orbital shift. However, the observed identical T-dependence for both 199 T 1 and 63 T 1 reveals the presence of an hyperfine field transferred from Cu spins, whose fluctuations are essentially responsible for the nuclear relaxation of 199Hg. We discuss the implications of these findings, compared to recent NMR results in Hg-1201 [23].

An Interpretive Basis of the Proton Nuclear Magnetic Resonance Hyperfine Shifts for Structure Determination of High-Spin Ferric Hemoproteins. Implications for the Reversible Thermal Unfolding of Ferricytochromec‘ fromRhodopseudomonas palustris

An NMR approach to determining the solution molecular structure of a high-spin ferric hemoprotein, 13 kDa ferricytochrome c‘ from Rhodopseudomonas palustris (Rp), has been investigated. In parallel with the use of appropriately tailored 1D and 2D experiments to provide scalar and dipolar correlations for the strongly relaxed and hyperfine-shifted heme cavity residues, we explore an interpretive basis of the large hyperfine shifts for noncoordinated residues which could provide constraints in solution structure determination for high-spin ferric hemoproteins. It is shown that the complete heme can be uniquely assigned in spite of the extreme relaxation properties (T1s 1−8 ms). Sufficient scalar connectivities are detected for strongly relaxed protons (T1 ≥ 4 ms) to uniquely assign residues on both the proximal and distal sides of the heme. The spatial correlations indicate that the structure is homologous to the four-helix bundle observed for other cytochromes c‘. The pattern of large hyperfine shifts for noncoordinated residues is shown to be qualitatively reproduced by the dipolar shifts for a structural homolog based on an axial zero-field splitting of ∼12 cm-1. It is concluded that, when this approach is combined with more conventional 2D methods for the diamagnetic portion of the protein, a complete structure determination of a five-coordinate ferric hemoprotein should be readily attainable. It is shown that the ferricytochrome c‘ unfolds reversibly at high temperature and that there exists at least one equilibrium intermediate in this unfolding that is suggested to involve helix separation from the heme.

17O NMR in high- Tc superconductor Tl 2Ba 2CaCu 2O y

17O NMR measurements have been performed between 10 and 400 K on an overdoped sample of Tl 2Ba 2CaCu 2O y ( T c = 103 K). The electric field gradient parameters were deduced for all the oxygen sites. The temperature dependence of the magnetic hyperfine shift was measured for all these sites. No thermal variation of the shift was detected down to T c for oxygen in the TlO reservoir plane. As for oxygen in the CuO 2 plane the temperature dependence of the shift is similar to that for 205Tl NMR line from thallium defects in the Ca layer measured in the same powder sample. This similarity is consistent with the single spin fluid model. The spin contribution to 17K iso( T) and magnetic hyperfine constant 17A iso were deduced.

Further copper NMR studies of the electron superconductor Nd 2CuO 3.7F 0.3

The temperature dependence of the magnetic shifts in the normal state of the anion-doped superconductor Nd 2CuO 3.7F 0.3 are presented. The shifts due to the neodymium moments are subtracted off, to leave magnetic hyperfine shifts with a linear temperature dependence. In contrast to YBCO the temperature-dependent term in the shift for B applied parallel to the c-axis of the tetragonal crystal is about seven times larger than the shift when B is applied perpendicular to the c-axis.

Magnetic nuclear spin-lattice relaxation in NMR of orthorhombic crystals in the presence of strong quadrupole coupling

A review is given of some NMR techniques developed in experiments on high-temperature superconductors. Multiexponential relaxation which appears in the T1 measurements when NMR lines are split by quadrupole interactions is discussed for the case of magnetic relaxation. The change in the form of relaxation is followed as the quadrupole Hamiltonian starts to perturb the otherwise pure Zeeman spin states (defined by Iz). Orthorhombic symmetry is assumed in the analysis, which is shown to greatly simplify the data reduction to obtain the magnetic hyperfine shift, the electric field gradient and the nuclear spin-lattice relaxation rate.

Spin-lattice relaxation, NQR 63Cu and NMR 205Tl in Tl 2Ba 2CuO 6+δ

We measured the nuclear spin-lattice relaxation rate of 63Cu and 205Tl, the magnetic hyperfine shift of 205Tl, and the NQR of 63Cu in the raw of Tl 2Ba 2CuO 6+δ with different T c( δ) in the range 3–400 K, to investigate low-frequency spin dynamics in perovskite CuO 2 layers. The possibility is discussed of explaining the obtained results in terms of the “antiferromagnetic Fermi liquid” model proposed by Monien, Millis and Pines. We found that T c is lowered and growth of the uniform spin susceptibility χ( q = 0) takes place which is accompanied by a decrease in the intensity of a short-wave AF spin correlation between copper atoms in the CuO 2 plane.

In vivo sodium chemical shift imaging

The shift reagents thulium(III) 1,4,7,10-tetraazacyclododecane N,N',N",N"'tetramethylenephosphonate (TmDOTP5-), and dysprosium(III)triethylenetetramine-hexaacetate (DyTTHA3-) are compared in this work for their uses in sodium chemical shift imaging (NaCSI). In a series of experiments using phantoms we evaluated the relative contributions of bulk magnetic susceptibility (BMS) effects and hyperfine shifts to the induced 23Na chemical shift for these two shift reagents. The ratios of BMS effects to hyperfine shifts suggest that TmDOTP5- should be a more effective shift reagent than DyTTHA3- for 23Na NMR spectroscopy as well as NaCSI. The dependence on pH and free Ca2+ concentration of the 23Na NMR frequency shift induced by TmDOTP5- was evaluated. It was found that TmDOTP5- produces good spectral resolution under physiologic conditions. Examples presented from in vivo NaCSI experiments using TmDOTP5- to study diffusion in the posterior chamber of the rabbit eye and to monitor the rate of clearance of aqueous fluid from the anterior chamber demonstrate the effectiveness of this new shift reagent and of the NaCSI technique for in vivo studies.

17O NMR in YBa2Cu3O6.65. Discrimination between t-J and two-band models

17 O NMR has been performed between 10 and 360 K on an oriented powder of YBa 2 Cu 3 O 6.65 ( T c =60 K). The temperature dependence of the magnetic hyperfine shift (MHS) tensors has been followed for the O(2,3) and O(4) sites. For O(4) nuclei, the MHS stays constant above T c , whereas for the O(2,3) sites it scales linearly with the macroscopic susceptibility χ m . This demonstrates that the origin of the temperature dependence of χ m is to be found within the CuO 2 plane. Two methods are presented to discriminate between the t - J model and two-band models: (a) the comparison of the temperature dependence of the isotropic K iso and the axial part K ax of the O(2,3) MHS, (b) a scaling between the experimentally measured products K 2 iso T 1 T in 17 O and 89 Y. From the second method, our results indicate the existence of an oxygen 2p-band with a density of states per spin direction of 0.11 to 0.19 eV -1 at -1 .

Analysis of the 63,65Cu NMR data as a function of oxygen concentration in YBa 2Cu 3O 7−δ

We compare the 63,65Cu NMR data at δ = 0 and 0 < δ ⩽ 0.35 in single crystal samples of YBa 2Cu 3O 7−δ. The lack of δ-dependence in the c component of the magnetic hyperfine shift (MHS) and in the nuclear spin-lattice relaxation rate is associated with the existence of localized Cu (3d) holes. For δ ≠ 0 samples, in addition to the variation of the number of free charge carriers, the system is perturbed by the presence of oxygen vacancies acting as local defects. In the concentration range (0 < δ < 0.1), the 2D character of the oxygen p-holes seems to be reinforced. This may change the coupling between localized Cu (3d) and mobile O (2p) holes, as reflected in the temperature dependence of antiferromagnetic fluctuations of Cu spins. The data on MHS show a strong suppression of its spin component, even for δ = 0.1.

NMR study of 63,65 Cu in YBa 2 Cu 3 O 7 to 6.65 single crystals

Abstract We report 63 Cu NMR nuclear spin-lattice relaxation rates (NSLRR) and magnetic hyperfine shift (K cc ) of copper Cu(2) in the CuO 2 planes of YBa 2 Cu 3 O 7−δ as a function of temperature and δ. The independence of K cc and NSLRR (above 120 K) on δ associated with the existence of localized Cu(3d) holes. We comment on the difference in the NSLRR between the δ = 0 and δ ≠ 0 samples which appear below 120 K. It is interpreted as an indirect consequence of the changes in the oxygen 2p electronic band caused by the introduction of oxygen vacancies in the system.

NMR study of 17 O in high T c superconducting oxides

We present the temperature dependence of the Magnetic Hyperfine Shift tensors of 17 O nuclei for the sites within the CuO 2 plane (site O(I)) and in the BaO, LaO, SrO plane (O(II) site) in the compounds YBa 2 Cu 3 O 7 , YBa 2 Cu 3 O 6.65 , La 1.85 Sr 0.15 CuO 4 and Bi 2 Sr 2 CaCu 2 O 8 . For O(I) sites, the isotropic part of the tensor reflects the polarisation of the Oxygen 2s orbitals by the neigboring Cu d-holes and the temperature dependence of the susceptibility. We show that in YBa 2 Cu 3 O 6.65 , the spins of the oxygen p-holes have their own degree of freedom above 120 K.

17O NMR study of YBa 2Cu 3O 7−δ ( Tc=92 K)

We have performed 17O NMR in YBa 2Cu 3O 7 oriented powder samples in the temperature range 10–360 K for the orientation H 0∥ c and H 0⊥ c. The Electric Field Gradient (EFG) and Magnetic Hyperfine Shift (MHS) tensors have been determined for the four oxygen sites in the structure. The isotropic (axial) part of the MHS tensor were found to be equal to 0.21 (0.08)% for the O(2,3) site in the CuO 2 plane and to 0.04(0.05)% for the bridging oxygen O(4). Both were found temperature independent in the normal state. Below T c, they vanish to zero and the data for the MHS K cc [ O(2,3)] show that this decrease is faster than expected from BCS theory. The coupling between the localized spins at the Cu (2) sites and the mobile oxygen p-holes is discussed in the light of these results.

NMR evidence for localized spins on Cu(2) sites from Cu NMR in YBa2Cu3O7 and YBa2Cu3O6.75 single crystals.

We report $^{63}$,65Cu NMR spectra and nuclear spin-lattice relaxation data for ${\mathrm{YBa}}_{2}$${\mathrm{Cu}}_{3}$${\mathrm{O}}_{7}$(${\mathrm{T}}_{\mathrm{c}}$=91 K) and ${\mathrm{YBa}}_{2}$${\mathrm{Cu}}_{3}$${\mathrm{O}}_{6.75}$(${\mathrm{T}}_{\mathrm{c}}$${=5}_{7}$ K) single crystals between 45 and 300 K. An analysis of the spin-lattice relaxation rates gives evidence for localized electronic spins on the planar Cu(2) sites. In ${\mathrm{YBa}}_{2}$${\mathrm{Cu}}_{3}$${\mathrm{O}}_{6.75}$ both fourfold and twofold oxygen-coordinated Cu(1) are observed; the latter experience the same quadrupolar coupling (${\ensuremath{\nu}}_{Q}$\ensuremath{\simeq}31.5 MHz) as the Cu(2) sites but a nearly zero magnetic hyperfine shift and a much slower relaxation rate (${d}^{10}$ configuration).

Proton nuclear magnetic resonance hyperfine shifts as indicators of tertiary structural changes accompanying the Bohr effect in monomeric insect hemoglobins.

Proton nuclear magnetic resonance hyperfine shifts as indicators of tertiary structural changes accompanying the Bohr effect in monomeric insect hemoglobins.

K39Nuclear Magnetic Resonance in KMnF3and Temperature Dependence of the Generalized Order Parameter at the Structural Phase Transition

The $^{39}\mathrm{K}$ nuclear-magnetic-resonance spectrum in KMn${\mathrm{F}}_{3}$ single crystal displays, below the structural phase transition at 186 \ifmmode^\circ\else\textdegree\fi{}K, a second-order quadrupole shift of the central line superimposed to the magnetic hyperfine shift. From the analysis of the data the value of the quadrupole coupling constant below ${T}_{C}$ is derived and is shown to be proportional to the square of the rotational displacement parameter for the Mn${\mathrm{F}}_{6}$ octahedra. The temperature dependence of this generalized order parameter below ${T}_{C}$ is described by a critical exponent $\ensuremath{\beta}=\frac{1}{2}$ but shows a renormalization of the transition temperature of about 10% ascribed to large critical fluctuations starting about 15 \ifmmode^\circ\else\textdegree\fi{}K from the transition temperature. Near the transition temperature a critical exponent $\ensuremath{\beta}$ of about $\frac{1}{3}$ is obtained.