Ligand Hyperfine Interaction of Ti²⁺ in CdS and CdSe on Sites with Trigonal Symmetry C_3v

Abstract

An E P R investigation is made of the hyperfine interactions with ligand nuclei (SHFS) of the TiZ+ centre in single crystals of hexagonal CdS and CdSe on sites with trigonal point symmetry C3". From the spectra experimental evidence is given for the magnetic nonequivalence of the twelve next-nearest ligands (cadmium) in wurtzite-type crystals. The SHFS-constants for the first three cadmium lattice shells for wurtzite are calculated using MO-theory. From the SHE'S-constants the probability is estimated of finding the delocalized 3d-electrons of the Ti2+ ion in the 5s-orbitals of the cadmium ligands.Es wird die Ligandenhyperfeinwechselwirkang (SHFS) von Ti"+-Zent,ren in Einkristallen von hexagonalem CdS und CdSe auf Platzen niit trigonaler Punktsymmetrie C3" mittels E P R untersucht. &fit den Spektren wird die magrietische Kicht.aquivalenz der zwolf ubernLchsten Nachbarn (Kadmium) in Wurtzit experimentell nachgewiesen. Die SHFS-Konstanten der ersten drei Kadmium-Gitterschalen fur Wurtzit werden mit der MO-Theorie berechnet. Aus den SHFS-Konstanten wird die Aufenthaltswahrscheinlichkeit der delokalisierten 3d-Elektronen des Ti2+-tons in den 5s-Orbitalen der Kadmiumnachbarn bestimmt IntrodlietionHyperfine interactions with ligand nuclei are a powerful mechanism to investigate covalency and charge transfer effects in crystals since a measurement of the hyperfine structure provides a direct measurement of the unpaired spin transfer [l]. Owing to the appreciable portion of covalent binding and the small natural abundance of chalcogen isotopes with nuclear magnetic moments, 11-VI compounds are suitable substances to investigate superhyperfine splitting (SHFS) with the next-nearest neighbours (Cd). The coupling constants of' interaction were found to be nearly isotropic and the observed spectra are described even in the case of the hexagonal crystals of wurtzite type structure with the assumption that the twelve next-nearest ligands belong only t o one lattice shell and having the same SHFS tensor. By reason of the local symmetry of a lattice site in wurtzite, C3", one expects however that the twelve next-nearest ligands belong to three distinct lattice shells and should show differences even in the isotropir SHFS constants.I n this paper experimental evidence is given for the magnetic nonequivalence of the twelve next-nearest ligands (Cd) in the hexagonal 11-VI compounds. At 27 O K in Ti-doped CdS and CdSe single crystals very we11 resolved SHFS lines are observed in the fine structure EPR transitions of the Ti2+ centre due to magnetic interactions of the unpaired 3d electrons with Cdlll and Cd113 nuclei and care-

ENDOR Study of the Superhyperfine Interaction of Ti2+ in CdS

“…The values of the coupling constants determined from the ENDOR measurements confirm the data from the analysis of the E P R measurements given in [4] and support the principal features of the model. However, even for H I I c the ENDOR experiment yields a clear distinction of the three shells of the first Cd neighbours.…”

“…A precise determination of the anisotropic SHFS constants and their direction cosines, however, was not possible by EPR. I n this paper results are given of ENDOR nieasurenients niade on the Ti2+ centre in CdS to prove the niodel of the SHFS interaction given in [4].…”

“…43, DDR-1040 Berlin, DDR. The tensors A: * have orthorhombic symmetry; some statements about the principal axes can be made by reasons of symmetry (for details see [4]). The Ti2f centre with the four sulfur and the twelve Cd ligands is shown in Fig.…”

EPR of iron‐boron centres in silicon

“….-. I/s X ar x + 2 The trigonal field splitting parameter 6 is determined byThe same relations(22) to(25) but with modified values a , a', and il are valid if covalent effects are taken into account[21]. The evaluation of the Zeeman effect within the ground doublet yields in first order the following values […”

Magnetostructural Dependencies in $3d^2$ Systems: The Trigonal Bipyramidal V$^{3+}$ Complex

“…For an overview on the properties of 3d 2 type systems the reader may consult Refs. [32][33][34][35]. Studying the relation between the magnetic properties and the compound's structure provides a deeper knowledge for the existing zerofield splitting (ZFS) [36,37], quantum character of magnetic anisotropy and all field dependent properties.…”