Low-Temperature Studies of CuFe2S3 and CuFeS2 by 63,65Cu NMR in the Internal Magnetic Field

• Published in: Journal of low temperature physics Vol. 185; no. 5-6; pp. 618 - 626
• Main Authors: Gavrilenko, Andrey Nikolaevich, Pogoreltsev, Aleksandr Iliich, Matukhin, Vadim Leonidovich, Korzun, Barys Vasilyevich, Schmidt, Ekaterina Vadimovna, Sevastianov, Iliya Germanovich
• Format: Journal Article
• Language: English
• Published: New York Springer US 2016
• Subjects: Characterization and Evaluation of Materials; Condensed Matter Physics; Magnetic Materials; Magnetism; Physics; Physics and Astronomy; electronic structure calculations; Quadrupole parameters; Spin density distribution; NMR in the internal magnetic field; Hyperfine interactions; Electron density distribution
• ISSN: 0022-2291; 1573-7357
• DOI: 10.1007/s10909-016-1550-8

The resonance
63
,
65
Cu NMR spectra in the internal magnetic field in cubanite CuFe
2
S
3
and chalcopyrite CuFeS
2
were studied experimentally at 77 K. Using a cluster approach,
ab initio
evaluation of the electric field gradient (EFG) at the nuclei of copper in both compounds was performed. The calculations were carried out by the self-consistent restricted method of Hartree–Fock with open shells (SCF-LCAO-ROHF). The largest clusters for which calculations were made had a formula of Cu
7
Fe
14
S
29
n
for cubanite and Cu
9
Fe
10
S
28
n
for chalcopyrite, where
n
is the cluster charge. The best-fit values of the quadrupole parameters (quadrupole frequency
ν
Q
and the asymmetry parameter of the EFG tensor
η
)—determined experimentally (
ν
Q
≈
 7.30 MHz and
η
≈
 0.82) and by calculation (
ν
Q
≈
 7.38 MHz and
η
≈
 0.87)—were obtained for a cluster Cu
7
Fe
14
S
29
10
for cubanite. Similarly, the best-fit values of the quadrupole parameters—determined experimentally (
ν
Q
≈
 1.29 MHz and
η
≈
 0.34) and by calculation (
ν
Q
≈
 1.40 MHz and
η
≈
 0.50)—were obtained for a cluster Cu
9
Fe
10
S
28
-
4
for chalcopyrite. For these clusters, maps of the electron density distribution in the neighborhood of quadrupole nucleus of copper were built. Based on the analysis of the resulting electron density distribution, it is supposed that the bond in these compounds is not quite covalent. Evaluations of the hyperfine interaction constants were made and maps of the spin density distribution in the neighborhood of quadrupole nucleus of copper were built. The energy level diagram calculated in the high-spin ROHF approximation defined chalcopyrite as a compound with a very narrow LUMO–HOMO gap rather well and is consistent with the notion of this compound as a semiconductor.