Fe-based semimagnetic semiconductors with two anions

Abstract

͑Cd 1Ϫx Fe x )͑Te 1Ϫy Se y ) crystals have been studied both theoretically and experimentally. In such a system, a part of Fe 2ϩ ions are located in crystal environments of a lowered symmetry. The energy level structure of these ions is substantially modified with respect to that of the Fe 2ϩ ion in one-anion ͑ternary͒ crystal. Regarding magnetic properties, the most essential modification occurs when an Fe 2ϩ ion is surrounded by three atoms of Te and one Se atom. Then, a doublet becomes a ground state of the magnetic ion, while, in the case of a ternary crystal, the ground state of an Fe 2ϩ ion is always a nonmagnetic singlet. In consequence, for two-anion systems, we observe a Curie-like paramagnetism instead of an otherwise revealed temperature independent (Tр10 K͒ Van Vleck paramagnetism. Although, in the present work, we are concerned mostly with ͑Cd 1Ϫx Fe x )͑Te 1Ϫy Se y ), a similar behavior is also observed for various crystals based on zinc and mercury. The results of our photoconductivity measurements indicate that the ground energetic state of an Fe 2ϩ ion can take several localizations in the band structure of the matrix crystal. A specific position depends on a configuration of nearest neighbors of an Fe 2ϩ ion, i.e., if it is surrounded by four Te, or three Te and one Se, etc. Concluding, we show that doped with Fe quaternary II-VI semimagnetic semiconductors demonstrate magnetic and optical properties essentially different from that of Fe doped ternary II-VI semimagnetic semiconductors.

Magnetic susceptibility and compositional dependence of the energy gap in Cd1-xCoxTe

“…This conclusion is in agreement with the large values of d-d exchange constants |J 1 | and |J 2 | for Co-based compared to Mn-and Fe-based II-VI DMSs [3,24]. The large d-d interaction in Cd 1−x Co x Te is also consistent with the large p-d interaction reflected in the value of β [25,26]. According to the superexchange model of Larson et al [27], developed for Mn-based DMSs, one can state roughly that a larger magnitude of β leads to a larger d-d interaction between the magnetic moments of the transition metal ions.…”

“…Besides the modified Brillouin function contribution of single ions to the magnetization, which saturates at high fields, there can also be a significant high-field susceptibility contribution due to strong interactions of second-and more-distant-neighbour pairs of magnetic ions [18,19]. For a kth-neighbour pair of Co 2+ ions with exchange integral J k , the eigenvalues of their Hamiltonian are given by [6,18]…”

LiCo1−yByO2 As Cathode Materials for Rechargeable Lithium Batteries

“…Co 3+ is known to be in the low spin state S = 0. We have investigated the electronic structure and the related magnetic properties of the d 6 shell of Co 3+ and Fe 2+ ions in the low spin state in prior works. , As a result, these are Van-Vleck ions, with a Van-Vleck paramagnetic contribution χ p that is larger than the diamagnetic one χ d , so that χ 0 = χ p + χ d is positive. In the cubic crystal-field environment, the term χ p is temperature independent, and is associated with the coupling between the nondegenerate (i.e., nonmagnetic) ground state and the magnetic excited state of these ions by the spin−orbit operator.…”

The complex structure of Fe2+(3d6) magnetism in HgSe1−ySy mixed crystals

“…It turns out that magnetic properties of mixed anion crystals Cdl_xFexTel_rSey are substantially different [4,5]. In that case the susceptibility does not exhibit Van Vleck behaviour, which led the authors to the conclusion that the local environment of the FeZ+(3d 6) ion may essentially influence its energy spectrum.…”