17O relaxation time and NMR sensitivity of cerebral water and their field dependence

2001 ◽  
Vol 45 (4) ◽  
pp. 543-549 ◽  
Author(s):  
Xiao-Hong Zhu ◽  
Hellmut Merkle ◽  
Jae-Hwan Kwag ◽  
Kamil Ugurbil ◽  
Wei Chen
Keyword(s):  
Relaxation Time ◽  
Field Dependence ◽  
Nmr Sensitivity

Role of magnetic interparticle coupling on the field dependence of the superparamagnetic relaxation time

2005 ◽  
Vol 72 (21) ◽  
Author(s):  
W. C. Nunes ◽  
L. M. Socolovsky ◽  
J. C. Denardin ◽  
F. Cebollada ◽  
A. L. Brandl ◽  
...  
Keyword(s):  
Relaxation Time ◽  
Field Dependence ◽  
Superparamagnetic Relaxation

Spin-lattice relaxation in rare-earth salts: field dependence of the two-phonon process

1961 ◽  
Vol 264 (1319) ◽  
pp. 485-495 ◽  
Keyword(s):  
Relaxation Time ◽  
Rare Earth ◽  
Field Dependence ◽  
Lattice Relaxation ◽  
Internal Field ◽  
Effective Field ◽  
Rare Earth Ions ◽  
Spin Lattice Relaxation ◽  
Dipolar Fields ◽  
Van Vleck

The field dependence of the two phonon process is computed taking into account hyperfine and dipolar fields. The general Gorter-Van Vleck-Hebel-Slichter (G.V.H.S.) formalism is adapted to the rare-earth ions, the effective Hamiltonian techniques of the previous paper being used. It is found that a distinction is necessary between salts with g ⊥ = 0 and those with g ⊥ ≠ 0. The Brons-Van Vleck formula holds rigorously for the former case, and predicts a relaxation time inversely proportional to τ − 1 = 0.15 × 10 11 + 6 × 10 7 T 2 s − 1 where H hyp 2 and H dip 2 are the mean square internal hyperfine and dipolar fields, respectively. For the case of g ⊥ ≠ 0, a quite different dependence of relaxation time on field is found by the use of th e G.V.H.S. formalism : 1 / T 1 ∝ ( H 2 + μ H hyp 2 + 1 2 μ ′ H dip 2 ) / ( H 2 + H hyp 2 + 1 2 H dip 2 ) The terms μ and μ' are computed explicitly for the general case. The Van Vleck effective internal field approach predicts μ = 1, μ' = 2, but in general we find that μ < 1 and μ' may be greater than 2. This arises from the failure of the effective field approximation and from processes neglected by Van Vleck in his treatment; specifically, the effects of spin correlation and of off-diagonal terms in the dipolar Hamiltonian which ‘help’ the oscillating electric field to flip spins. The term μ' will in general decrease with increasing temperature for Hainan processes, and be temperature-independent for resonance processes. It should increase with concentration for both. Agreement with experiment is not very good for the case of dysprosium ethyl sulphate (g ⊥ = 0), but the feature of μ' > 2 for salts with g ⊥ ≠ 0 seems to be characteristic of many magnetic salts.

A Phenomenological Description of the MPS Signal Using a Model for the Field Dependence of the Effective Relaxation Time

2015 ◽  
Vol 51 (2) ◽  
pp. 1-4 ◽  
Author(s):  
Daniel Schmidt ◽  
Florian Palmetshofer ◽  
David Heinke ◽  
Uwe Steinhoff ◽  
Frank Ludwig
Keyword(s):  
Relaxation Time ◽  
Field Dependence ◽  
Phenomenological Description

scholarly journals Терагерцовая фотопроводимость в графене в магнитном поле

2020 ◽  
Vol 54 (4) ◽  
pp. 388
Author(s):  
Ю.Б. Васильев ◽  
С.Н. Новиков ◽  
С.Н. Данилов ◽  
С.Д. Ганичев
Keyword(s):  
Magnetic Field ◽  
Relaxation Time ◽  
Field Dependence ◽  
Electron Scattering ◽  
Terahertz Radiation ◽  
Magnetic Field Dependence ◽  
Signal Amplitude ◽  
Strong Increase ◽  
The Magnetic Field ◽  
Photoconductivity Signal

Abstract The terahertz photoconductivity in epitaxial graphene grown on SiC substrates is investigated in a magnetic field. The magnetic-field dependence of the photoresponse signal amplitude is examined at different electron densities, bias currents, and terahertz radiation intensities. The experimental results are explained well by a photoconductivity mechanism based on the heating of electrons by terahertz radiation. A strong increase in the photoconductivity signal with increasing magnetic field caused by an increase in the relaxation time due to the suppression of electron-electron scattering is observed.

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