title: Paramagnetic hyperfine splitting in the Eu Mössbauer spectra of CaF(2):Eu.
abstract: (151)Eu Mössbauer spectra in zero magnetic field of highly dilute (0.1 mol%) Eu(2+) ions in CaF(2) showed an almost temperature-independent asymmetrically split pattern, arising from the paramagnetic hyperfine interaction AS. I in a cubic crystal field with slow electron spin relaxation; in a small external magnetic field B of 0.2 T such that gμ(B)B>A an almost symmetrical pattern was observed. Both the spectra with and without external field are well described using the spin Hamiltonian and previous electron paramagnetic resonance data. A more concentrated (2 mol% Eu(2+)) sample exhibited a strongly broadened symmetrical resonance line due to an increased Eu-Eu spin relaxation rate; in an external magnetic field of 0.2 T the Mössbauer spectra exhibited further broadening and additional magnetic structures due to the reduced relaxation rate. When a large field of 6 T was applied such that gμ(B)B is much larger than the crystal field splitting, a fully resolved hyperfine pattern was observed at 2.5 K, with an effective field at the Eu nuclei of -33.7 T; at higher temperatures superimposed patterns originating from excited electronic states were observed in the spectra. The present results on the highly dilute CaF(2) : 0.1%Eu(2+) sample deliver a straightforward explanation for previous observations of a seemingly large dependence of the Eu(2+) isomer shift on europium concentration.
authors.affiliation: Department of Physics, Faculty of Science, University of Paderborn, Warburger Straβe 100, D-33098 Paderborn, Germany.
authors.forename: J
authors.initials: J
authors.lastname: Selling
authors.forename: B
authors.initials: B
authors.lastname: Bielemeier
authors.forename: G
authors.initials: G
authors.lastname: Wortmann
authors.forename: J A
authors.initials: JA
authors.lastname: Johnson
authors.forename: E E
authors.initials: EE
authors.lastname: Alp
authors.forename: T
authors.initials: T
authors.lastname: Chen
authors.forename: D E
authors.initials: DE
authors.lastname: Brown
authors.forename: C E
authors.initials: CE
authors.lastname: Johnson
authors.forename: S
authors.initials: S
authors.lastname: Schweizer