Unraveling the impact of nonmagnetic Sc substitution on the magnetic properties of La2NiMnO6 double perovskite
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Abstract The structural, electronic, and magnetic properties of a sol-gel prepared series of La 2 Ni 1− x Sc x MnO 6 compounds have been extensively studied using x-ray diffraction, x-ray absorption near edge structure, and dc magnetization techniques, respectively. The entire series was isostructural and exhibited the La 2 NiMnO 6 double perovskite P2 1 /n monoclinic structure. The nonmagnetic Sc 3+ substitution led to the evolution of competing magnetic phases in La 2 Ni 1− x Sc x MnO 6 . The substitution also caused an increase in lattice parameters, cell volume, and bond lengths. Consequently, Sc 3+ dilution resulted in a dramatic decrease in Curie temperature, suggesting a reduction in the strength of the Ni 2+ –O 2− –Mn 4+ superexchange ferromagnetic interaction. The Sc 3+ substitution generated antisite defects, which significantly suppressed the saturation magnetization of the system. The competing magnetic interactions observed in the La 2 Ni 1− x Sc x MnO 6 system are discussed in terms of cation disorder, cation valances, and changes in the bond lengths/angles, caused by the Sc 3+ substitution.Keywords:
Superexchange
Isostructural
Molecular geometry
Monoclinic crystal system
Based on the helical and rotational symmetries and Tersoff potential, the structural parameters, i.e., bond lengths and bond angles, have been investigated for armchair single-wall carbon nanotubes. The bond lengths and bond angles are determined for several radii tubes of various lengths. Results for armchair tubes show that one bond length is greater than that of the graphite while the other is smaller. Furthermore, the tube length is found to have significant effects on these bond lengths and bond angles. We have also recalculated the variation of these bonds under hydrostatic pressure. With the application of pressure, the bond lengths compress and the larger bond length decreases faster with pressure in comparison to the shorter one. As a consequence, at some critical pressure the bond lengths become equal. An analysis regarding the cross-sectional shape of the nanotubes and its pressure dependence has also been done. At some particular pressure, the first transition from circular to elliptical cross section takes place. For (10,10) tube the first transition pressure is found to be equal to $2.2\phantom{\rule{0.3em}{0ex}}\mathrm{GPa}$.
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Molecular geometry
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Molecular geometry
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Single bond
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Energy minimization
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Single bond
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We have studied bond length and bond angle of a series of phenols. For present study the molecular modelling and geometry optimization of all the compounds were carried out with MOPAC software using MINDO/3 methods. We have conclude that the order of bond lengths between C-O, C-C, C-H and O-H atoms have been changed by changing the position of the substituents i.e., from ortho to para substitution. The C-C-C band angles have the same value while the C-C-O and C-O-H band angles differ from their normal values on substitution.
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Single bond
Bond energy
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The influence of the substitution with nonmagnetic ions on the magnetic moment M and the Curie temperature TC has been investigated in Y3-2xCa2xInyAlzFe5-x-y-zO12 (0 ≤ x ≤ 1; 0 ≤ y ≤ 1; 0 ≤ z ≤ 2). The statistics of superexchange interactions developed by Gilleo has been applied. An additional decrease of the superexchange interactions caused by the magnetic ions excluded from ferrimagnetism has been taken into account. The results obtained show that the correction improves the accuracy in the prediction of the magnetic moment and the Curie temperature. The higher TC in V-substituted garnets has been explained with the indirect influence of the nonmagnetic V ion which increases the strength of the superexchange interactions.
Superexchange
Ferrimagnetism
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Saturation (graph theory)
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We investigate structural parameters, i.e., bond lengths and bond angles of isolated uncapped zigzag single-wall nanotubes in detail. The bond lengths and bond angles are determined for several radii tubes by using a theoretical procedure based on the helical and rotational symmetry for atom coordinates generation, coupled with Tersoff potential for interaction energy calculations. Results show that the structure of zigzag tubes is governed by two bond lengths. One bond length is found to have a value equal to that of graphite, while the other one is larger. Furthermore, the tube length is found to have significant effect only on larger bond length in zigzag tubes. With the application of the pressure, only the larger bond length compresses, the other one remaining practically constant. At some critical pressure, this bond length becomes equal to constant bond length. This behavior of bond lengths is different from those of armchair tubes. An analysis regarding the cross sectional shape has also been done. At some higher pressure, transition from circular to oval cross section takes place. This transition pressure is found to be equal 2.06GPa for (20,0) tube. Some comparison with chiral tubes has also been made and important differences on bond length behavior have been observed.
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Molecular geometry
Single bond
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The crystal structure of [Ni(en)(OH2)4][NO3]2 is reported (en = ethylenediamine). The mean Ni–N bond length is 2.065 A, and N–Ni–N bond angle 83.6°. N–M–N angles in en complexes, and O–M–O angles in acetylacetonates, are discussed in terms of their relation to M–N or M–O bond length. A conformational analysis of tris-en complexes is carried out so as to compare the predicted effect on the N–M–N angle of varying the M–N bond length with the observed relation between N–M–N angle and M–N length.
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The effect of ring-puckering angle on the structural parameters (bond lengths and angles) involved in the ring strain of a series of four-membered heterocycles (1–16) was theoretically demonstrated by using the ab initio methods MP2 and HF, and the DFT methods PBE1PBE, B3LYP, SVWN5 with 6-31+G(d,p) as basis set. The results revealed that the bonds within the ring (C–X and C–C) are the most sensitive to puckering angle changes. The variation of the C–X and C=Y bond lengths as function of puckering angle are determined by a balance between the 1,3 repulsive interactions and the electronic nature of the heteroatoms X and Y. Particularly, for azetidines and phosphetanes, the C–X and C=Y bond lengths exhibit a major increase at axial conformations. In general, the C–C bond length decreases with the puckering angle for all heterocycles. While the heteroatom–H bonds (in the ring skeleton) are very sensitive to geometric changes, exhibiting an increasing behaviour for equatorial conformations and a decreasing behaviour for axial conformations highly puckered (ϕ > −20°). The C–X–C angle decreases monotonically with the puckering angle, increasing the Baeyer strain on the studied molecules. Finally, all methods predicted a similar behaviour for the studied parameters as function of the puckering angle, although some smaller differences in the predictions of their respective values, especially at HF level, were observed.
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