Gd 3+ -RE 3+ Exchange Interactions in Rare-Earth Fluoride Crystals (RE = Ce, Nd, Yb)

M.L. Paradowski and L.E. Misiak Institute of Physics, Marie Curie-Skłodowska University, pl. M. Curie-Skłodowskiej 1, 20-031 Lublin, Poland

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Received: February 9, 2004

The investigation of Gd 3+ -doped LaF 3 , La 0.9 Ce 0.1 F 3 , CeF 3 , La 0.9 Nd 0.1 F 3 , LiYF 4 , and LiY 0.9 Yb 0.1 F 4 single crystals at 4.2K was carried out in order to study the Gd 3+ -RE 3+ exchange interactions (RE = Ce, Nd, Yb). The exchange interactions were estimated by the application of the molecular-field model at liquid-helium temperature, using the g shift from the isostructural diamagnetic hosts LaF 3 and LiYF 4 to the paramagnetic hosts. The lattice dynamics is studied by analysing spin-Hamiltonian parameters in the light of the superposition model and the rotational invariance theory for phonon-induced contributions to spin-Hamiltonian parameters. It is suggested from the rotational invariance mechanism for phonon-induced contributions to spin-Hamiltonian parameters that the rotational contributions influence the exchange interactions significantly. Further, the distortions caused by the La 3+ /Ce 3+ , La 3+ /Nd 3+ , and Y 3+ /Yb 3+ substitutions affect significantly the 4f 7 electron--phonon interactions, as well as the exchange interactions. The magnitude of the isotropic exchange interactions is larger for more symmetrical charge distribution of the 4f 7 shell.

DOI: 10.12693/APhysPolA.105.445 PACS numbers: 63.20.Kr, 75.30.Et, 75.30.Hx, 76.30.Kg