A. Shengelaya et al., LOW-TEMPERATURE ESR-SPECTRA OF NICKEL-DOPED NACL-CRYSTALS, Zeitschrift fur Physik. B, Condensed matter, 101(3), 1996, pp. 373-376
Paramagnetic resonance of Bridgman-grown NaCl crystals nominally doped
with divalent nickel was studied over the temperature range from 4 K
to 300 K. The broad isotropic EPR line with g = 2.12 divided by 2.23 a
nd Delta H-pp = 280 divided by 780 G was detected at temperatures high
er than 130 K for samples of various thermal history. The origin of th
ese spectra was attributed to aggregated and precipitated Ni2+ ions. A
t temperatures lower than 40 K another ESR signal was registered. It w
as an anisotropic one, the intensity of which strongly depends upon th
e temperature. This spectrum results from substitutional Ni+ ions with
tetragonally distorted surrounding along a [100] direction. The angul
ar dependence of the ESR line positions was fitted to an appropriate s
pin-Hamiltonian with the g-factor components g(parallel to) and g(perp
endicular to) equal to 2.86 and 2.10, respectively. The temperature-de
pendence of the signal intensity at temperatures between 4 and 110 K h
as been interpreted in terms of a transition from the static to dynami
c Jahn-Teller effect.