Direct measurement of the exchange interaction between rare-earth ions in metallic Van Vleck paramagnets

1975 ◽  
Vol 11 (11) ◽  
pp. 4450-4454 ◽  
Author(s):  
C. Rettori ◽  
D. Davidov ◽  
A. Grayevskey ◽  
W. M. Walsh
Keyword(s):  
Rare Earth ◽  
Exchange Interaction ◽  
Direct Measurement ◽  
Rare Earth Ions ◽  
Van Vleck

On the origin of the exchange interaction between rare-earth ions in Van Vleck pnictides

1975 ◽  
Vol 53 (4) ◽  
pp. 290-292 ◽  
Author(s):  
D. Davidov ◽  
J.M. Bloch ◽  
R. Levin ◽  
C. Rettori ◽  
D. Shaltiel
Keyword(s):  
Rare Earth ◽  
Exchange Interaction ◽  
Rare Earth Ions ◽  
Van Vleck

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.

EPR SPECTRA OF PAIRS OF INTERACTING RARE-EARTH IONS

1967 ◽  
Vol 45 (2) ◽  
pp. 403-428 ◽  
Author(s):  
J. M. Baker ◽  
A. E. Mau
Keyword(s):  
Rare Earth ◽  
Exchange Interaction ◽  
Quadrupole Interaction ◽  
Electric Quadrupole ◽  
Dipole Interaction ◽  
Rare Earth Ions ◽  
The Other ◽  
Epr Spectra

The EPR spectra of interacting pairs of Dy3+, Tb3+, and Ho3+ ions in rare-earth ethyl sulfates have been studied in order to determine the nature and magnitude of the interactions. The departures from dipole–dipole interaction are mostly rather small, except for the interaction between a pair of Dy3+ ions, one of which is in the ground doublet and the other in the first excited doublet at 16 cm−1. A discussion is given of the difficulties of differentiating between the effects of electric quadrupole–quadrupole interaction and virtual phonon exchange interaction.

High-Degree Exchange Interaction Between Rare-Earth Ions

1968 ◽  
Vol 21 (9) ◽  
pp. 620-623 ◽  
Author(s):  
J. M. Baker ◽  
R. J. Birgeneau ◽  
M. T. Hutchings ◽  
J. D. Riley
Keyword(s):  
Rare Earth ◽  
Exchange Interaction ◽  
Rare Earth Ions ◽  
High Degree

Characterization of Rare-Earth Fluoride Anti-Stokes Phosphors by Scanning arid Transmission Electron Microscopy

1971 ◽  
Vol 29 ◽  
pp. 142-143
Author(s):  
N. M. P. Low ◽  
L. E. Brosselard
Keyword(s):  
Electron Microscopy ◽  
Rare Earth ◽  
Elevated Temperatures ◽  
Stoichiometric Composition ◽  
Rare Earth Ions ◽  
Crystalline Solid ◽  
Precipitation Process ◽  
Rare Earth Fluoride ◽  
Earth Fluoride ◽  
Rare Earth Fluorides

There has been considerable interest over the past several years in materials capable of converting infrared radiation to visible light by means of sequential excitation in two or more steps. Several rare-earth trifluorides (LaF3, YF3, GdF3, and LuF3) containing a small amount of other trivalent rare-earth ions (Yb3+ and Er3+, or Ho3+, or Tm3+) have been found to exhibit such phenomenon. The methods of preparation of these rare-earth fluorides in the crystalline solid form generally involve a co-precipitation process and a subsequent solid state reaction at elevated temperatures. This investigation was undertaken to examine the morphological features of both the precipitated and the thermally treated fluoride powders by both transmission and scanning electron microscopy.Rare-earth oxides of stoichiometric composition were dissolved in nitric acid and the mixed rare-earth fluoride was then coprecipitated out as fine granules by the addition of excess hydrofluoric acid. The precipitated rare-earth fluorides were washed with water, separated from the aqueous solution, and oven-dried.

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