An EPR Investigation of Cr³⁺ and Ni^{2 +} in Synthetic Pyrite Crystals

Abstract

In many synthetic pyrite single crystals of high quality and purity we could detect Cr3 + and Ni2 + by EPR at 78 K as unwanted impurities. The assignment was possible by means of the isotopes Cr53 and Ni61, occurring in natural abundance. The paramagnetic centers exhibit unusual g-values. In case of Ni2 + a ligand hyperfine interaction could be observed beside the normal hyperfine interaction with the Ni61 nucleus. For some crystals the Cr 3 + signal intensity could be increased up to ten times by temperature increasement from 78 K to about 100 K. At 78 K the Cr3 + intensity was quenched by IR irradiation.

EPRInvestigation of Synthetic, Doped FeS2 and RuS2 Single Crystals

“…the spin has to be integer. The observation is similar to that of Ni2+ in FeS^ [5]. Therefore we analyzed the different resonance lines with the spinHamiltonian (see (3)) for electronic spin 5 = 1 and nuclear spin 1 = 0 and found a very good agreement with the experimental values as shown in Figure 4.…”

“…[4,5,6] and in RuS2 [7]. Yu et al performed sim ilar EPR measurements with FeS9 [8] that agree with ours essentially.…”

“…with elementary nickel and due to the spin value S = 1 we assigned Ni2+ on Ru site to the observed EPR resonance. The result is similar to that of Ni2+ in FeS7 [5]. We were not able to measure the weak HFS of the isotope 61 Ni with a nuclear spin 1 = 3/2 because of the broadened lines due to interactions with the nearest Ru neighbours (1 = 5/2 for "R u (12 %) and 101 Ru (17 %)).…”

“…Furthermore we were able to detect the signals expected at higher fields near 0. The received data can be described satisfactorily with the specialized spin-Hamiltonian for electronic spin 5 = 3/2 and the above nuclear spin [5]:…”

Quantitative EPR: Some of the most difficult problems

“…Though all the chromium centers ate crystallographically equivalent, one can divide them into four groups which are generally different with respect to the external and microwave magnetic fields (see details of the structure in papers [9] and [10]). As has been already pointed out, such groups require individual treatment.…”