Investigations of the spin Hamiltonian parameters for the cubic Mn²⁺ centers in ZnX (X = S, Se, Te) and CdTe

Abstract

The spin Hamiltonian parameters (g factors and the hyperfine structure constants) for the cubic Mn 2+ centers in ZnX (X = S, Se, Te) and CdTe are investigated theoretically using the perturbation formulas of these parameters for a tetrahedral 3d 5 cluster containing both the crystal-field and charge-transfer contributions. The relevant molecular orbital coefficients are uniformly determined from the cluster approach, and the calculated spin Hamiltonian parameters are in good agreement with the observed values. The g-shifts of the g factors related to the pure spin value gs (& 2.0023) arising from the charge transfer contributions are opposite (positive) in sign and much larger in magnitude than those from the crystal field contributions. On the other hand, the contributions from the charge-transfer mechanism to the hyperfine structure constants are the same in sign and about 20%-30% in magnitude of those from the crystal-field mechanism. The importance of the charge transfer contributions increases significantly with the increase of the covalency and the spin-orbit coupling coefficient of the ligand, i.e., S 2-< Se 2-< Te 2-.Résumé : Nous faisons une étude théorique des paramètres du Hamiltonien de spin (les facteurs g et les constantes de structure hyperfine) pour les centres Mn +2 cubiques dans ZnX (X = S, Se, Te) et CdTe, en utilisant les formules de perturbation de ces paramètres pour un amas (cluster) tétraèdre 3d 5 , contenant les contributions du champ du cristal et de transfert de charge. Les coefficients orbitaux moléculaires pertinents sont déterminés uniformément à partir de l'approche en amas et les paramètres calculés du Hamiltonien de spin sont en bon accord avec les valeurs observées. Les déplacements g des facteurs reliés à la valeur de spin pur g s ( = 2,0023) causés par les contributions de transfert de charge sont de signe opposé (positif) et d'amplitude beaucoup plus grande que ceux causés par les contributions du cristal. D'autre part, les contributions à la structure hyperfine provenant du mécanisme de transfert de charge sont de même signe et d'amplitude correspondant à 20-30 % de celles causées par les mécanismes cristallins. L'importance des contributions dues au transfert de charge croît significativement avec la covalence du coefficient du couplage de spin-orbite du ligand, c.-à-d. S 2 < Se 2 <Te 2 .[Traduit par la Rédaction]

Designing quantum dots for solotronics

“…The rate of spin relaxation of isolated ions increases with the strength of the spin–orbit interaction405556, which depends on the magnetic ion and the host material57. Therefore it is reasonable to use QDs based on semiconductors with light anions: sulphides, oxides and nitrides, as they exhibit a weak spin–orbit interaction.…”

Investigations on the defect structures for Mn2+ in CdSe nanocrystals and bulk materials and the criterion of occupation for Mn2+ in CdX (X = S, Se, Te) nanocrystals

“…H SO , H Ze , and H hf denote the SO coupling, electronic Zeeman term, and hyperfine coupling interactions, respectively. 21 Thus, the fourth-order perturbation formulas of the SHPs could be established for a trigonally distorted tetrahedral 3d 5 cluster containing both the CF and CT mechanisms, by considering the perturbation contributions from trigonal CFs, SO coupling, electron Zeeman term, and off-diagonal part of the electrostatic Coulombic and hyperfine interactions, 13,22 that is,…”

“…The above quantities without and with prime stand for the diagonal and offdiagonal matrix elements, respectively, for the SO coupling, orbital angular momentum, and hyperfine coupling equivalent operators within the irreducible representations T 2 and E of T d group. 22 They can be theoretically determined from the relevant free-ion values and the corresponding molecular orbital coefficients based on the cluster approach containing both the CF and CT contributions. 23 The denominators E j (j = 1-9) 14,16,23 They can be determined from the energy matrices for a 3d 5 ion in cubic symmetry in terms of the cubic CF parameter Dq and the Racah parameters B and C. 18 V and V 0 are the trigonal CF parameters.…”

“…By using the Mn 2+ -Se 2À distances R (≈2.571 and 2.573 Å 24,25 ) at the core of CdSe:Mn 2+ nanocrystals and in bulk materials as well as the Slater-type selfconsistent-field wave functions, 32,33 the group overlap integrals S π , S σ , and S s and the integral W can be calculated. From the normalization conditions, the orthogonality relationships and the approximation relationships related to covalency factor N, 22…”

“…H SO , H Ze , and H hf denote the SO coupling, electronic Zeeman term, and hyperfine coupling interactions, respectively 21 . Thus, the fourth‐order perturbation formulas of the SHPs could be established for a trigonally distorted tetrahedral 3d 5 cluster containing both the CF and CT mechanisms, by considering the perturbation contributions from trigonal CFs, SO coupling, electron Zeeman term, and off‐diagonal part of the electrostatic Coulombic and hyperfine interactions, 13,22 that is, …”