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2D Magnetic Systems
Published in Ram K. Gupta, Sanjay R. Mishra, Tuan Anh Nguyen, Fundamentals of Low Dimensional Magnets, 2023
A superexchange is defined as an indirect exchange interaction between non-neighboring magnetic ions which is mediated by a non-magnetic ion, placed in between the magnetic ions, e.g. Mn2+ manganese ions connected via O2− oxygen ions in MgO. Superexchange is a second-order process that is derived from the second-order term of perturbation theory.
Electronic Properties of Perovskite Oxides
Published in Gibin George, Sivasankara Rao Ede, Zhiping Luo, Fundamentals of Perovskite Oxides, 2020
Gibin George, Sivasankara Rao Ede, Zhiping Luo
The superexchange is the antiferromagnetic coupling of the nearest transition metal ions with antiparallel spins through a non-magnetic anion with paired spins. In magnetically ordered perovskites, such as LaCrO3, PbCrO3, CaMnO3, and LaFeO3, the electronic conductivity is through superexchange. On the other hand, LaCoO3 behaves completely opposite; it is metallic at temperature 500 K, paramagnetic at 100 K, and diamagnetic at low temperatures. The reason for this transition is the different spin states of Co atom (HS, IS, LS); however, the spin state responsible for each transition is still under debate (Korotin et al. 1996). Currently, researchers are assuming that LS (t2g6) is the ground state and responsible for the insulating phase, whereas IS (t2g5eg1) is for the metallic phase instead of HS (t2g4eg2) (Hansteen et al. 1998). These transitions extensively studied in Pr0.5Ca0.5CoO3 and Pr0.5Sr0.5CoO3 compounds. Pr0.5Ca0.5CoO3 shows the ferromagnetic metallic phase at low temperatures near Curie temperature (Tc = 230 K) (Tsubouchi et al. 2002). However, in the case of Pr0.5Sr0.5CoO3, the metallic phase is noticed at room temperature and the insulating phase is observed around 75 K. The changes in transitions are more complicated by the electron-donating ability of Pr3+ cations to Co3+ cations, and Co4+ cations remain intact in LS (t2g5) (García-Muñoz et al. 2016). However, the Pr0.5Ca0.5CoO3 and Pr0.5Sr0.5CoO3 compounds have different phases at room temperature and low temperatures, suggesting that Ca2+ and Sr2+ cations play their part in governing metal–insulator transition.
Coordination chemistry and magnetic properties of copper(II) halide complexes of quinoline
Published in Journal of Coordination Chemistry, 2022
Christopher P. Landee, Firas F. Awwadi, Brendan Twamley, Mark M. Turnbull
The higher aromatic homologs quinoline (quin) and isoquinoline (iquin) have also been employed for preparation of complexes with 1st row MX2 salts, but somewhat less frequently. Structures of the bis-quin ZnCl2 [19], ZnBr2 and ZnI2 complexes [20], along with the CoCl2 [21], CoBr2 [22] and CoI2 [23], and the MnBr2 [24] complexes have all been reported. Only three such complexes have been reported for iquin: the ZnCl2 [25], and the CuCl2 and CuBr2 [26] compounds, although for the latter two, only the structure of the bromide compound is known. No related structures of acridine (the next higher homolog) complexes of 1st row transition metals have been reported, although there are a number of Pt and Pd compounds known [27]. Although there have been a number of (quin)2Cu(I)X complexes prepared and their structures reported [28], we were surprised to see that although the corresponding Cu(II) halide compounds have been reported and characterized by IR [29], single-crystal structure data have not been reported. Given the known azaphilicity of the Cu(II) ion and the multiple potential halide-mediated magnetic superexchange pathways available, these compounds seemed to be natural targets for magnetostructural correlation analysis. Here we present the synthesis, structure, and magnetic properties of (quin)2CuX2 (X = Cl, 1, or Br, 2).
Multiferroic and exchange bias in La0.85Sr0.15FeO3−δ perovskite nanoparticles
Published in Philosophical Magazine, 2019
E. K. Abdel-Khalek, K. Abdullah, E.A. Mohamed
To reveal the origin of the exchange interactions between the Fe and oxygen ions, the charge density distribution maps have been estimated from Rietveld refinement powder XRD data by using GFourier software [24]. Figure 3 shows the charge density distribution maps along (x, y, 0), (0, y, z) and (x, 0, z) in the orthorhombic unit cell of La0.85Sr0.15FeO3−δ nanoparticle sample. It is clear that the charge density distribution is different along (x, y, 0), (0, y, z) and (x, 0, z) for the Fe–O bonds. There is some continuous charge density distribution for Fe–OII which indicated that there is partial covalency in Fe–OII bonds [25,26]. These results are agreement with the structural data, the following Mössbauer and magnetic results. Thus, the presence of the superexchange interaction of ferromagnetic within antiferromagnetic which is due to the interactions via apical oxygen ion denoted as OI [27].
Transition metal salts of quinoline: synthesis, structure and magnetic behavior of (QuinH)2[MX4]·2H2O [Quin = quinoline; M = Mn, Co, Cu, Zn], (QuinH)2[MnBr2(H2O)2](Br)2 and (QuinH)[Cu(Quin)Br3]
Published in Journal of Coordination Chemistry, 2018
Christopher P. Landee, Jeffrey C. Monroe, Robert Kotarba, Matthew Polson, Jan L. Wikaira, Mark M. Turnbull
Compounds 1 and 2. The two cobalt complexes are very similar in their magnetic properties (Table 5). First, their Curie constants are identical within the experimental uncertainties (2.76(2) cm3·K mol−1); second, their Curie constants at low temperature are essentially the same as those at high temperature; third, the exchange strength of the chloride compound is about two thirds as large as the bromide. This near-equivalence of exchange strengths is in sharp contrast with the strengths of the copper members of this family for which the bromide interaction is 4.5 times that of the chloride, 6.2 K versus 1.37 K (Table 5). Similar ratios of JBr/JCl have been seen in other CuX4 complexes which interact through halide–halide contacts [27]. It has been proposed that the relative strength of JBr to JCl in these compounds was due to the larger ionic radius of the bromide ions, leading to increased wave-function overlap in the superexchange pathway. While that may be true for the copper complexes, it does not seem to apply to the cobalt compounds in this study.