Temperature Dependence Of Knight Shift Research Articles

47Ti and 49Ti nuclear magnetic resonance in TiH 2

The NMR of 47Ti and 49Ti has been observed in TiH 2 in the temperature range 155–310 K. The Knight shift and spin-lattice relaxation rate ( T l T) − were found to be temperature dependent. The shift varied from 0.245 ± 0.002% at 310 K to 0.319 ± 0.002% at 155 K, whereas T 1 T varied from 22 ± 1 s K at 310 K to 48.8 ± 3 s K at 155 K. From the temperature dependences of Knight shift and magnetic susceptibility a core polarization hyperfine field of − (126 ± 8) kOe was deduced. Applying the tight binding approximation the data for the cubic phase (310 K) have been partitioned into spin (s,p,d) and orbital (p,d) contributions. In the tetragonal phase (below 310 K) a temperature dependence of the d band density of states at the Fermi level was deduced. An influence of the lower symmetry on the spin-lattice relaxation behaviour is discussed.

Pulsed nuclear magnetic resonance of 59Co in Co3S4

Nuclear magnetic resonance of 59Co in Co3S4, which had been considered to be a simple Pauli paramagnet, has been reinvestigated by a pulsed method. Free-induction decay or spin-echo signals from A and B sites in the spinel structure have been observed. The signal from the magnetic A site shows a temperature-dependent Knight shift, and disappears suddenly at 58 K with decreasing temperature, suggesting the onset of a magnetically ordered state. The hyperfine coupling constant is roughly estimated to be −10 kOe/μB from the K-χ plot. The signal from the nonmagnetic B site, which shows a textbooklike quadrupolar powder pattern, is strong at low temperatures but the effect of the magnetic A site on the B site was not detected. The nuclear spin-lattice relaxation shows the Korringa-type behavior with (T1T)−1=13±2(s K)−1 for 59Co at the A site.

Radio-Spectroscopic Studies of Magnetic Properties of High Temperature Superconductors

Abstract We have performed 17O and 63Cu NMR measurements in YBa2Cu3O7-δ (δ ≈ 0.15) oriented powder samples at CuO2 plane sites Cu(2) and 0(2, 3) in the temperature range 10-300 K. The temperature dependent Knight shift K(T) and spin lattice relaxation rate T1 -1-(T) of O(2, 3) yield K2T1T = const in accordance with the presence of free carriers at plane oxygen sites. A sharp decrease of T1 -1 of Cu(2) below 120 K is associated with the opening of a gap in the spectrum of antiferromagnetic spin fluctuations of localized copper 3 d9 electrons. The comparison of different temperature dependences of spin densities at the Cu and O sites shows the presence of two nearly independent spin systems. A close similarity of YBa2Cu3O7-δ a with heavy fermion superconductors is discussed.

NMR of 17 O and 63 Cu in uniaxially aligned superconductor YBa 2 Cu 3 O 7-δ

We have performed 17 O and 63 Cu NMR measurements in YBa 2 Cu 3 O 6.85 oriented powder samples at the CuO 2 plane sites Cu(2) and O(2,3) in the temperature range from 10 to 300 K. The temperature dependent Knight shift K and spin lattice relaxation rate T −1 1 of O(2,3) yield K 2 T 1 T = const in accordance with the presence of free carriers at the plane oxygen sites. A sharp decrease of T −1 1 of Cu(2) below T AF ≈ 1.5 T c is associated with the opening of a gap in the spectrum of antiferromagnetic spin fluctuations of localized copper 3d 9 electrons. Comparison of the different temperature dependences of spin densities at the Cu and O sites shows the presence of two nearly independent spin systems in close similarity with heavy fermion superconductors. A magnetic mechanism of high temperature superconductivity in doped CuO 2 layers is suggested.

Studies of the electronic phase transition in Lu5Ir4Si10 and Lu5Rh4Si10 by 175Lu-NMR.

Pulsed nuclear magnetic resonance of $^{175}\mathrm{Lu}$ (I=(7/2) was used to study the electronic phase transition of samples ${\mathrm{Lu}}_{5}$${\mathrm{Ir}}_{4}$${\mathrm{Si}}_{10}$ and ${\mathrm{Lu}}_{5}$${\mathrm{Rh}}_{4}$${\mathrm{Si}}_{10}$ under atmospheric pressure from 49 to 310 K. A calculation of the powder line shape in the quadrupole regime for I=(7/2 shows that the critical frequencies, particularly that of the singularity, are sensitive to the change of the electric-field-gradient (EFG) asymmetry and the Larmor frequency. From the singularity near \ensuremath{\nu}=${\ensuremath{\nu}}_{0}$, the EFG asymmetry of the lutetium nucleus is estimated to be \ensuremath{\eta}\ensuremath{\simeq}0.4. The temperature coefficient of the lutetium EFG asymmetry as estimated from the temperature-dependent shift is close to 3\ifmmode\times\else\texttimes\fi{}${10}^{\mathrm{\ensuremath{-}}5}$ ${\mathrm{K}}^{\mathrm{\ensuremath{-}}1}$. This small variation of the EFG asymmetry suggests that the crystal structure remains unchanged in the temperature range studied. The possible formation of charge-density-wave states at 83 and 145 K for the two compounds, respectively, is indicated by anomalous variations of the temperature-dependent Knight shift. A loss of the electronic density of states at the Fermi level, as inferred from the jump discontinuity of the Knight shift, is consistent with previous measurements of resistivity and the magnetic susceptibility on these samples. From the correlation of the Knight shift with the magnetic susceptibility, the hyperfine field is determined to be 0.5 and 0.7 MOe, a value consistent with the previous measurements of rare-earth metals. The NMR of $^{45}\mathrm{Sc}$ (I=(7/2) in ${\mathrm{Sc}}_{5}$${\mathrm{Ir}}_{4}$${\mathrm{Si}}_{10}$, isostructural with the above two compounds, was used as a baseline measurement to illustrate the anomalous behavior observed for $^{175}\mathrm{Lu}$ in ${\mathrm{Lu}}_{5}$${\mathrm{M}}_{4}$${\mathrm{Si}}_{10}$ (M=Ir,Rh).

Knight shift of 115In in REInAg 2 alloys and mixed valent YbInAu 2

Large temperature dependent Knight shift (KS) of 115In has been measured in REInAg 2 alloys with the Heusler structure, usually found in compounds of transition metals. In SmInAg 2, interaction of the excited state | J=7/2〉 with the ground state | J=5/2〉 is clearly observed. In mixed valent YbInAu 2, a weak maximum in KS at ≃100 K is discernible.

Theory of temperature-dependent knight shift in narrow-gap semiconductors

We derive a theory of the temperature-dependent Knight shift in narrow-gap semiconductors. As an example, we calculate the temperature variation of the Knight shift of 207Pb in p-PbTe, which agrees fairly well with experiment.

Exchange Enhanced Pauli Paramagnetism of ScCo2

The temperature dependence of magnetic susceptibility, χ, of a cubic Laves phase compound ScCo 2 was measured in the temperature range 4.2–1018 K and found to have a broad maximum at about 600 K. The temperature dependent Knight shift, K , of Sc was obtained from NMR experiment below room temperature. The K vs χ plot gives a straight line resulting in -41 kOe/ µ B as a transferred hyperfine field from Co. It was concluded that ScCo 2 is an exchange enhanced Pauli paramagnet of the same kind of YCo 2 and LuCo 2 .

Muon Knight shift investigations in LaAg1-xInx

Muon Knight shift measurements are performed in the pseudobinary intermetallic compound LaAg1-xInx (CsCl structure). Negative, temperature-dependent Knight shift values are found. This observation is discussed in terms of a negative transferred hyperfine field between the La 5d states and the muon, whose magnitude varies from -3 kG mu B-1 to -10 kG mu B-1 for 0<or=x<or=0.3.

NMR Study of Magnetic State of Co in Pseudobinary (Y1-xGdx)Co2System

The spin echo NMR of 59 Co in the (Y 1- x Gd x )Co 2 system was observed in both magnetically ordered and paramagnetic states. In YCo 2 , the Knight shift of 59 Co was found to be linear in susceptibility, leading to a hyperfine coupling constant of -89 kOe/ µ B . The zero-field center frequency in the ordered state and both the Knight shift and the relative integrated intensity in the paramagnetic state were observed for over all the concentration. The field dependence of integrated intensity and temperature dependence of Knight shift were also measured in the vicinity of the critical concentration. The results indicate the coexistence of two types of Co atoms in the whole concentration range; one has a magnetic moment which couples antiparallel with the Gd moment and the other has no moment.

Temperature-dependent Knight shift in cadmium

The temperature-dependent Knight shift in cadmium has been investigated using our recent results for the temperature-dependent spin susceptibility. Our calculation of the spin susceptibility includes the effect of lattice potential which includes the effect of electron-electron interaction via an effective one-particle approximation and spin-orbit interaction. Thermal effects of lattice expansion and electron-phonon interactions have been included in our calculation in a pseudopotential formalism. Our results for the temperature-dependent Knight shift show improvement on the earlier theoretical results and agree well with the experimental results.

Magnetic properties of electrons and holes in metallic Si:P and Si:B

We present new NMR data on the ${\mathrm{P}}^{31}$ resonance in Si:P and ${\mathrm{B}}^{11}$ resonance in Si:B for samples in the impurity concentration range from 5 \ifmmode\times\else\texttimes\fi{} ${10}^{18}$ to 9 \ifmmode\times\else\texttimes\fi{} ${10}^{19}$ ${\mathrm{cm}}^{\ensuremath{-}3}$. The data give further information about the magnetic properties of the charge carriers in these metallic samples. These data, taken in conjunction with recent NMR data for ${\mathrm{Si}}^{29}$ by Sasaki, Ikehata, and Kobayashi in Si:P in the same concentration range place certain restrictions upon models which have been introduced to interpret magnetoresistance and spin-susceptibility data. Both ${\mathrm{P}}^{31}$ and ${\mathrm{Si}}^{29}$ data in Si:P exhibit a temperature dependence of linewidth and Knight shift for $T$ below 4.2 K. The results are compared to the ESR spin-susceptibility measurements of Quirt and Marko and of Ue and Maekawa. It is observed that the temperature dependence of the Knight shift and linewidth can be almost entirely accounted for by the temperature dependence of the spin susceptibility. The NMR data support a simple model in which all donor electrons or acceptor holes participate in a single, interacting system. They give no confirmation to the existence of the local magnetic moments which have been invoked to explain the negative magnetoresistance in $n$-type heavily doped semiconductors, but can also not rule out the existence of such moments.

X-ray study of anharmonicity in AuGa2

Au${\mathrm{Ga}}_{2}$ has been studied extensively in recent years because of its rather surprising temperature-dependent Knight shift and magnetic susceptibility. To gain some information on its vibrational properties we have measured the temperature dependence of the integrated x-ray intensities of various Bragg reflections from 300 to 625\ifmmode^\circ\else\textdegree\fi{}K. We have detected the anharmonic anisotropic Ga atom vibration. The ratio of the anharmonic to harmonic potential coefficients for the Ga atom is about half that of other ionic fluorite compounds. The vibrational mean-square amplitudes of Au and Ga are found to be equal to within experimental error, while in other fluorite compounds these relative amplitudes differ by 50%. The temperature dependence of the x-ray intensities was found to be anomalously large. To fit the data a conventional quasiharmonic treatment would require a Gruneisen parameter ${\ensuremath{\gamma}}^{\ensuremath{'}}=4.6$ which is more than twice the value expected from measured expansion coefficients, specific heat, and bulk modulus. We show that this large value of ${\ensuremath{\gamma}}^{\ensuremath{'}}$ is most likely associated with the ${C}_{11}\ensuremath{-}{C}_{12}$ shear modulus which appears to be both volume and temperature dependent. This temperature dependence is shown to be consistent with the thermal depopulation of the high density of states just below ${\ensuremath{\epsilon}}_{F}$ and is consistent with the high-temperature Knight-shift behavior.

NUCLEAR MAGNETIC RESONANCE IN LIQUID MANGANESE

We report measurements of the Knight shift (κ55) and spin-lattice relaxation time (T1) for Mn55 in liquid Mn and in the solid γ (FCC) and δ (BCC) phases over the temperature range 1 350 ⩽ T ⩽ 1 575 K. The value of κ55 in liquid Mn at 1 525 K is - 0.820 ± 0.005 % and 1/T1 is 2.2 ± 0.1 × 104 s-1. Detailed analysis of the temperature dependent Knight shifts and magnetic susceptibilities (χ) show that the d-spin susceptibility (χd) is responsible for roughly 75 % of the total susceptibility, the remainder being due mainly to orbital paramagnetism (χorb). The values of χd in liquid and solid δ-Mn are equal to within about 2 % and both are greater than in γ-Mn by about 10 %. Core polarization hyperfine couplings in the range - 225 ± 25 kG/Bohr magneton are deduced for all three phases. The relaxation rates in liquid and solid are consistent with Korringa relaxation by itinerant d-electrons.

A Model Pseudopotential in Metallic Properties

AbstractA new pseudopotential model (distinct from the Ashcroft model) having only one parameter rc (core radii) of the metal has been proposed. The present model as well as Ashcroft's model have been used in evaluation of several properties like electrical resistivity and thermoelectric power of liquid metals, electrical resistivity of solid metals, temperature dependence of Knight shift at constant volume and constant pressure, and Fermi energy and density of states of simple metals. A new correction term for thermoelectric power has been given, which gives a better result for lithium and cesium. The results obtained have been compared with possible experimental and theoretical data. Good agreement has been achieved.

Superconducting and Other Electronic Properties ofLa3In,La3Tl, and Some Related Phases

The low-temperature specific heats of ${\mathrm{La}}_{3}$In and ${\mathrm{La}}_{3}$Tl were measured in the superconducting and the normal state, the latter being stabilized in a magnetic field of 90 kOe. From these data, the thermodynamic critical fields and other thermodynamic properties could be determined. High and strongly varying electronic densities of states near the Fermi level are derived from magnetic-susceptibility measurements and confirmed by strongly temperature-dependent Knight shifts on the ${\mathrm{In}}^{115}$ nuclei in ${\mathrm{La}}_{3}$In and on the ${\mathrm{Tl}}^{203}$ and ${\mathrm{Tl}}^{205}$ nuclei in ${\mathrm{La}}_{3}$Tl. All remarkable properties of ${\mathrm{La}}_{3}$In and ${\mathrm{La}}_{3}$Tl, suggest that these compounds belong to the class of strong-coupling superconductors and are closely related to the behavior of fcc La under pressure.

NMR and magnetic susceptibility of the intermetallic pseudo-binary compounds Ce 1− xR xAl 3 with R=Gd, Tb and Er

The NMR and magnetic susceptibility of the intermetallic pseudo-binary compounds Ce 1− x Gd x Al 3 ( x=0·01; 0·03; 0·05; 0·07), Ce 0·95Tb 0·05Al 3 and Ce 0·975Er 0·025Al 3 were investigated. The susceptibility is given by the sum of a temperature independent term and a Curie-Weiss one. The last one results from the contribution of the localized free-ion magnetic moments of all the rare-earth ions which are also responsible for the strong temperature dependent Knight shifts of the NMR lines of 27Al nuclei via the exchange polarization of the conduction electrons. The 27Al NMR spectra exhibit besides the line due to Al sites surrounded in the first coordination sphere as in CeAl 3 a second peak with a lower Knight shift due to Al nuclei positioned in the vicinity of a Gd, Tb or Er ion.

MAGNETIC SUSCEPTIBILITY AND ANOMALOUS BEHAVIOUR OF KNIGHT SHIFT IN SmPt2 AND SmSn3

The temperature dependence of Knight shift of Sn119 in SmSn3 does not follow the prediction of White and Van Vleck. This anomalous behaviour is explained as due to the mixing of excited (J = 7/2) state into ground state of Sm3+ion by strong crystalline fields. The effect of strong crystalline fields on and χf is shown.

NMR Study of the Magnetic Properties of Dilute Al-Mn Alloys

High fields NMR experiments on Al-Mn alloys, complete previous results on this system. Together with the inhomogeneous Knight shift broadening of the Al 27 main line, two satellite lines could be detected. These effects are associated to the spin polarization induced by the impurity in the conduction band. One satellite, attributed to the first shell of neighours of the impurity, has a temperature dependent Knight shift suggesting a 15% reduction of the localized susceptibility from 0 to 300°K. The results are shown to be explained correctly by the frequency dependent Hartree Fock approximation if the experimental value of the susceptibility is used. When compared with more magnetic systems, the absence of qualitative difference for the macroscopic as well as microscopic properties, points, out that these results may be valid for the whole range of critical temperatures, and stresses the smoothness of the transition magnetism-non magnetism.

Temperature Dependence of Knight Shift of 115In in Hg-In Liquid Alloys

Temperature Dependence of Knight Shift of ¹¹⁵In in Hg-In Liquid Alloys