arXiv subjects
Publications and source records attributed to Z. Ropka.
By this Comment we would like to point out that the authors of Ref. 1 have ignored the orbital magnetism that makes the theory irrelevant to the real systems like NiO.It causes that the calculated result for the magnetic moment of NiO substantially disagrees with the experimental observation. PACS: 71.70.E, 75.10.D,
We criticize the model proposed by Mila et al. (Phys.Rev.Lett. 85 (2000) 1714) for the description of the V3+ ion in V2O3 by pointing out that it is completely artificial because the condition about the degenerate (doublet) orbital ground state required for the authors' model cannot be realized in the reality. We claim that the V3+ ion should be considered as described by the quantum numbers S=1 and L=3 and with taking into account the orbital moment and the intra-atomic spin-orbit coupling. PACS: 71.70.E, 75.10.D
In the commented Letter Vogt et al. (Phys.Rev.Lett. 84 (2000) 2969) claim the existence of a spin-state transition in YBaCo2O5. We think that this claim about the change from the low spin to high spin state upon cooling in YBaCo2O5 is errorneous. Keywords: magnetism, 3d ions, low spin.
Three fundamentally different electronic structures for 3d electron states in LaCoO3, discussed in the current literature, have been presented. We are in favour of the localized electron atomic- like approach that yields the discrete energy spectrum associated with the atomic-like states of the Co3+ ions in contrary to the continouos energy spectrum yielded by band theories. In our atomic-like approach the d electrons form the highly-correlated system 3dn described by S=2 and L=2. PACS No: 71.70.Ej : 75.10.Dg : 73.30.-m; Keywords: Mott insulators, electronic structure, crystal field, LaCoO3 Phys.Rev.Lett. 03-08-2000
It is argued that the formation of the non-magnetic state of FeS in external pressures above 6.5 GPa is in agreement with the prediction of the quantum atomistic solid-state theory, an extension of the crystal-field theory with the spin-orbit coupling incorporated, and is related with the change of sign of the off-cubic trigonal distortion marked by the change of the c/a ratio from >1.63 (magnetic) to <1.63 (non-magnetic). Keywords: highly-correlated electron system, crystal field, low-spin state, Fe2+ ion, spin-orbit coupling
By this Comment we would like to point out [2] that, though such consideration can be quite sophisticated, the consideration of a spin-pseudo-spin Hamiltonian has nothing in common with the reality. It means that such the consideration are useless as far as the properties of real systems are concerned.
It is argued that the V3+ ion in V2O3 should be considered as described by quantum numbers S=1 and L=3. It results from Hund's rules and means that the two d electrons form the highly- correlated electron system with the importance of the intra-atomic spin-orbit coupling. Keywords: highly-correlated electron system, crystal-field, spin- orbit coupling, orbital moment, V3+ ion. PACS: 71.70.E, 75.10.D, 75.30.Gw
We have shown that the V4+ ion with 1 d electron can have almost non-magnetic ground state under the action of the octahedral crystal field in the presence of the spin-orbit coupling and off-cubic distortions. Such the situation occurs in the hexagonal BaVS3. The fine discrete electronic structure with the weakly-magnetic Kramers-doublet ground state is the reason for anomalous properties of BaVS3. Keywords: crystal-field, spin-orbit, orbital moment. PACS: 71.70.E, 75.10.D
Postulates of the quantum atomistic solid-state theory (QUASST) have been presented. QUASST is an extension of the crystal-field theory and is applicable to compounds containing open-shell 3d, 4f and 5f atoms. QUASST points out the existence in a solid of the atomic-like discrete electronic structure determined by the crystal- field and spin-orbit interactions. This approach unifies the description of 3d and 4f ions and allows to bridge the atomic physics and the solid-state physics.
Magnetic moment of the Fe2+ ion in FeO, FeS and FeBr2 has been calculated within the quantum atomistic solid-state theory to substantially exceed a value of 4 muB in the magnetically-ordered state at 0 K. In all compounds the large orbital moment, of 0.7 - 1.1 muB, has been revealed. Our calculations show that for the meaningful analysis of electronic and magnetic properties of FeO, FeS and FeBr2 the intra-atomic spin-orbit coupling is essentially important and that the orbital moment is largely unquenched in 3d- ion containing compounds.
Magnetic moment of the Fe2+ ion in FeBr2 has been calculated to be 4.32 mB in the magnetically-ordered state at 0 K. It is composed from the spin moment of 3.52 mB and the orbital moment of +0.80 mB. These calculations show that for the meaningful analysis of e-m properties of FeBr2 the spin-orbit coupling is essentially important and that the orbital moment is largely unquenched.
It is pointed out that it is the local symmetry that determines the realization of the low- and high-spin state of the Co3+ ion. We can rigorously prove it treating the Co3+ ion as the highly-correlated electron system 3d6, that fulfiles the Hund's rules with taking into account the spin-orbit coupling. As the function of the sign of the off-cubic crystal-field distortion the magnetic or non-magnetic state is realized.
We argue that the Jahn-Teller theorem, if applied to 3d-ion compounds, has to be considered in the orbital+spin space. It is despite of the weakness of the intraatomic spin-orbit coupling.
It is shown that the d8 electron system occurring in the Ni2+ ion can have the non-magnetic ground state in the atomic scale formed by the Jahn-Teller effect. The tetragonal/trigonal off-cubic lattice distortion for the octahedral site causes the splitting of the triplet 3A2g into a singlet-doublet structure with the non-magnetic singlet lying lower provided the intra-atomic spin-orbit coupling is taken into account.
On basis of analysis of experimental results for more than 200 compounds with 3d and 4f elements we conjecture that atoms with unfilled 3d and 4f shells preserve much of their atomic properties, manifested by the discrete electronic structure, even then when they become the part of a solid. As a consequence, electronic and magnetic properties of the 3d-ion containing compounds are strongly affected by the existence of the atomic-like crystal-field fine electronic structure.
We argue that in LaCoO3 exists the fine electronic structure associated with the atomic-like states of the Co3+ ions and caused by the crystal-field and intra-atomic spin-orbit interactions. This low-energy fine electronic structure has to be taken into account for any meaningful analysis of electronic and magnetic properties of LaCoO3.
Electronic and magnetic (e-m) properties of FeBr2 have been surprisingly well described as originating from the Fe2+ ions and their fine electronic structure. The fine electronic structure have been evaluated taking into account the spin-orbit (s-o) coupling, crystal-field and inter-site spin-dependent interactions. The required magnetic doublet ground state with an excited singlet at D=2.8 meV results from the trigonal distortion. This effect of the trigonal distortion and a large magnetic moment of iron, of 4.4 mB, can be theoretically derived provided the s-o coupling is correctly taking into account. The obtained good agreement with experimental data indicates on extremaly strong correlations of the six 3d electrons in the Fe2+ ion yielding their full localization and the insulating state. These calculations show that for the meaningful analysis of e-m properties of FeBr2 the spin-orbit coupling is essentially important and that the orbital moment (0.74 mB) is largely unquenched (by the off-cubic trigonal distortion in the presence of the spin-orbit coupling).
The orbital and spin moment of the Ni2+ ion in NiO has been calculated at 0 K to be 0.54mB and 1.99 mB respectively. Such large orbital moment, more than 20% of the total moment of 2.53 mB, proves the need for the ''unquenching'' of the orbital moment in compounds containing 3d ions. It turns out that the spin-orbit coupling is indispensable for description of magnetic and electronic properties of 3d-ion compounds. These two findings, largely ignored at the nowadays in-fashion solid-state thories, call for an advanced solid-state physics theory.