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ESR Studies of Cu 2+ in NH 4 Cl Single Crystals between 4.2 and 453 °K. II. Theoretical Analysis: Vibrational Admixtures, Spin Polarization, and 〈 r −3 〉 for Cu 2+ Ions
Author(s) -
Pilbrow J. R.,
Spaeth J. M.
Publication year - 1967
Publication title -
physica status solidi (b)
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.51
H-Index - 109
eISSN - 1521-3951
pISSN - 0370-1972
DOI - 10.1002/pssb.19670200120
Subject(s) - hyperfine structure , chemistry , ion , ground state , hamiltonian (control theory) , atomic physics , lattice vibration , condensed matter physics , polarization (electrochemistry) , lattice (music) , single crystal , electron paramagnetic resonance , molecular physics , physics , nuclear magnetic resonance , crystallography , phonon , mathematical optimization , mathematics , organic chemistry , acoustics
Abstract The temperature dependence of the spin‐Hamiltonian parameters for two Cu 2+ centres in NH 4 Cl single crystals, which were reported in the previous paper (I), is analysed in detail. The results show that, apart from zero point vibrations, higher lattice modes also contribute to the admixture of the | x 2 – y 2 〉 state into the |3 z 2 – r 2 〉 ground state for these centres. For one of the centres there is also evidence that vibrations and reorientations of a single nearest neighbour NH 4 + ion contribute to the admixture. From the analysis, the temperature dependence of 〈 r −3 〉 3 z 2 – r 2 , a crystal field splitting parameter and the contact contribution to the hyperfine field at the Cu 2+ nucleus is obtained. All these quantities vary strongly with temperature and show sudden changes at the λ‐point ( −30.5 °C) for NH 4 Cl. The temperature dependence of the contact term in the hyperfine interaction can be qualitatively understood in terms of core spin polarization by taking into account the observed changes in the radial distribution of the 3d ground state. The analysis gives further support for the models proposed for the two Cu 2+ centres.