Theory of Tunneling Assisted Electron Spin–Lattice Relaxation

1971 ◽  
Vol 49 (12) ◽  
pp. 1620-1629 ◽  
Author(s):  
K. P. Lee ◽  
D. Walsh
Keyword(s):  
Lattice Relaxation ◽  
Zeeman Splitting ◽  
Spin Lattice Relaxation ◽  
Phonon Coupling ◽  
Orbital State ◽  
Strongly Coupled ◽  
Practical Applications ◽  
Spin Lattice ◽  
Jahn Teller ◽  
Temperature Relaxation

It is shown for an Eg orbital state and a tunneling splitting which is small compared with the Zeeman splitting that a strong Jahn–Teller coupling can lead to an enhancement of the direct spin–phonon coupling by several orders of magnitude. By comparing the theory with low temperature relaxation measurements on Cu2+ in a double nitrate the magnitude of several of the significant parameters associated with the Jahn–Teller problem is derived. A T2g orbital state strongly coupled to t2g modes of vibration can also have a strong spin–phonon coupling; the corresponding situation is briefly discussed.The strong coupling of the vibronic states to the lattice and the considerable range in the strength of this coupling have a number of practical applications.

scholarly journals NMR Spin-Lattice Relaxation and Tunnelling of Partially Deuterated Methyl Groups

1991 ◽  
Vol 46 (12) ◽  
pp. 1123-1130 ◽  
Author(s):  
H. Langen ◽  
W. Müller-Warmuth
Keyword(s):  
Lattice Relaxation ◽  
Proton Spin ◽  
Spin Lattice Relaxation ◽  
Spin States ◽  
Relaxation Rates ◽  
Spin Lattice ◽  
Conversion Rates ◽  
Temperature Relaxation ◽  
Field Cycling ◽  
Additional Influence

Abstract Proton spin lattice relaxation rates have been measured at 15 and 30 MHz and down to 5 K for the partially deuterated molecular crystals 4-F-toluene, 4-Cl-toluene, and 2,6-Cl2-toluene. The behaviour of these materials is governed by methyl group tunnelling. As compared with the undeuterated compounds, the low temperature relaxation is enhanced and the details depend on the removal of the symmetry coupling between rotator and spin states. The hindering barriers remain unchanged, the A to E conversion rates are faster, and relaxation is dominated by spectral density contributions J(2ωo) and J(2ω0). In one case an additional influence of level-crossing energy transfer on relaxation is observed. Field-cycling spectroscopy reveals steps rather than peaks if the proton spin Zeeman and tunnelling splittings match

Calculated Spin-lattice Relaxation of 103Ru Compared with Low Temperature Quadrupole Orientation Measurements

1994 ◽  
Vol 49 (1-2) ◽  
pp. 395-400 ◽  
Author(s):  
R. Markendorf
Keyword(s):  
Relaxation Time ◽  
Low Temperature ◽  
Reference Value ◽  
Lattice Relaxation ◽  
Lattice Relaxation Time ◽  
Spin Lattice Relaxation ◽  
Axially Symmetric ◽  
Quadrupole Field ◽  
Spin Lattice ◽  
Temperature Relaxation

Abstract The spin-lattice relaxation time T1 in 103Ru has been determined on the basis of the Dirac theory and strict relativistic band structure calculations. The low temperature relaxation time T(of 103Ru in an axially symmetric quadrupole field and the quadrupole moment Q have been measured by Green and Stone using the technique of low temperature quadrupole orientation. For the usual reference value T1 T, which corresponds to relaxation in a Zeeman spectrum, they obtain 39(6) sK, which exceeds our value by 134%. This large discrepancy is attributed to the fact that the spin relaxation by direct quadrupole scattering of conduction electrons, the so-called Mitchell contribution, is dominant. According to our calculations it amounts to 81% of the total relaxation rate. This contribution could not be included in the evaluation of the experimental data.

A multinuclear nuclear magnetic resonance study of methylammonium nitrate

1986 ◽  
Vol 64 (4) ◽  
pp. 773-776 ◽  
Author(s):  
Roderick E. Wasylishen
Keyword(s):  
Symmetry Axis ◽  
Lattice Relaxation ◽  
Nuclear Magnetic Resonance Study ◽  
Spin Lattice Relaxation ◽  
Magnetic Resonance Study ◽  
Strongly Coupled ◽  
Spin Lattice ◽  
Line Shapes ◽  
Liquid Phases ◽  
Plastic Phase

Deuterium nmr line shapes in the solid II phase of methylammonium nitrate (MAN) indicate that motion of the cation is restricted to internal rotations of the ND3 group about the C—N axis. In the high temperature plastic phase, solid I, of MAN, 2H, 14N, and 17O nmr results demonstrate that both the cation and anion undergo rapid overall rotations that result in complete averaging of all nuclear quadrupolar interactions. Spin-lattice relaxation results imply that rotations of the cation and anion are anisotropic and that the overall rotations are strongly coupled in both the solid I and liquid phases. At the melting point, overall rotations of the cation are only slightly faster in the liquid phase than in the solid I phase. In the solid I phase, in-plane rotations of the nitrate ion are about twice as rapid as end-over-end rotations of the C3 axis. In the neat liquid, rotations of the NO3− ion are more isotropic, with overall rotations being slightly faster than rotations about the symmetry axis.

Fullerenes Under Pressure Studied by 13C-NMR

1994 ◽  
Vol 359 ◽  
Author(s):  
Pascale Auban-Senzier ◽  
R. Kerkoud ◽  
D. Jerome ◽  
F. Rachdi ◽  
P. Bernier
Keyword(s):  
Ambient Pressure ◽  
Lattice Relaxation ◽  
Spin Lattice Relaxation ◽  
Spin Lattice ◽  
Doped Fullerenes ◽  
Jahn Teller ◽  
Exponential Behaviour ◽  
Superconducting Compound ◽  
Coulomb Correlations ◽  
C Nmr

ABSTRACTHigh pressure is an important parameter for the study of C60 and doped fullerenes as these molecular crystals are very compressible. 13C-NMR experiments under pressure in K3C60 have given access to the determination of the 13C Knight shift and the chemical shift of this superconducting compound. These NMR data do not reveal significant effects of Coulomb correlations in K3C60 and support a pairing mechanism for superconductivity mediated by intramolecular vibrations.We report also a 13C-NMR investigation of Rb4C60 under pressure and temperature. The temperature dependence of the spin-lattice relaxation rate clearly shows, under pressure, the increase of a linear contribution which gradually substitutes to the exponential behaviour present at ambient pressure. The activated relaxation is attributed to intrinsic spin excitations through the direct Jahn-Teller gap whereas the closing of a small indirect gap under pressure gives rise to a semimetal and a Korringa like relaxation.

Electron spin–lattice relaxation of Ni2+

1969 ◽  
Vol 47 (16) ◽  
pp. 1753-1756 ◽  
Author(s):  
K. P. Lee ◽  
D. Walsh
Keyword(s):  
Electron Spin ◽  
Lattice Relaxation ◽  
Magnesium Nitrate ◽  
Spin Lattice Relaxation ◽  
Direct Process ◽  
Effective Spin ◽  
Strongly Coupled ◽  
Spin Lattice ◽  
Phonon Bottleneck ◽  
Spin Triplet

The electron spin–lattice relaxation rate by the direct process for Ni2+ in lanthanum magnesium nitrate is surprisingly fast (5 × 103 s−1 at 1.55 °K). Ni2+ is a non-Kramers ion, however, and consequently is strongly coupled to the lattice in most cases. The effective spin triplet and the absence of both hyperfine structure and phonon bottleneck are optimum requirements for a maser material.

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