arXiv subjects

Z. Ropka

Publications and source records attributed to Z. Ropka.

At least 37 records · Page 2Linked to original sources

arXiv2004

Magnetism and fine electronic structure of UPd2Al3 and NpPd2Al3

We claim the existence of the f3 (U3+) configuration in UPd2Al3. It is in agreement with inelastic-neutron-scattering (INS) excitations and is consistent with the trivalent neptunium configuration in NpPd2Al3. We have derived set of CEF parameters for the U3+ state that reproduces the INS excitations and temperature dependence of the heat capacity. On basis of the crystal-field theory, extended to Quantum Atomistic Solid State Theory we argue that the magnetic moment of the uranium moment amounts at 0 K to 1.7-1.8 muB. Keywords: Crystalline Electric Field, Heavy fermion magnetism, UPd2Al3, NpPd2Al3 PACS: 71.70.E, 75.10.D

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arXiv2004

Strongly-correlated crystal-field approach to 3d oxides - the orbital magnetism in 3d-ion compounds

We have developed the crystal-field approach with strong electron correlations, extended to the Quantum Atomistic Solid-State theory (QUASST), as a physically relevant theoretical model for the description of electronic and magnetic properties of 3d-atom compounds. Its applicability has been illustrated for LaCoO3, FeBr2 and Na2V3O7. According to the QUASST theory in compounds containing open 3d-/4f-/5f-shell atoms the discrete atomic-like low-energy electronic structure survives also when the 3d atom becomes the full part of a solid matter. This low-energy atomic-like electronic structure, being determined by local crystal-field interactions and the intra-atomic spin-orbit coupling, predominantly determines electronic and magnetic properties of the whole compound. We understand our theoretical research as a continuation of the Van Vleck's studies on the localized magnetism. We point out, however, the importance of the orbital magnetism and the intra-atomic spin-orbit coupling for the physically adequate description of real 3d-ion compounds and 3d magnetism. Our studies clearly indicate that it is the highest time to ''unquench'' the orbital moment in solid-state physics in description of 3d-atom containing compounds. PACS No: 75.10.D; 71.70.E Keywords: magnetism, transition-metal compounds, 3d magnetism, crystal field, spin-orbit coupling, orbital magnetism

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arXiv2004

Ground state, electronic structure and magnetism of LaMnO3

We have calculated the discrete low-energy electronic structure in LaMnO3 originating from the atomic-like states of the strongly correlated 3d4 electronic system occurring in the Mn3+ ion. We take into account very strong intra-atomic correlations, crystal field interactions and the intra-atomic spin-orbit coupling. We calculated magnetic and paramagnetic state of LaMnO3 within the consistent description given by Quantum Atomistic Solid State Theory (QUASST). Our studies indicate that the intra-atomic spin-orbit coupling and the orbital magnetism are indispensable for the physically adequate description of electronic and magnetic properties of LaMnO3. Keywords: 3d oxides, crystal field, spin-orbit coupling, LaMnO3 PACS: 71.70Ej, 75.10Dg

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arXiv2004

Comment on Phys.Rev.Lett.'s paper: "Low temperature Electron Spin Resonance of the Kondo Ion in a heavy fermion metal YbRh2Si2"

We provide the microscopic explanation for the localized f state observed in a heavy fermion metal YbRh2Si2 by Prof. F. Steglich's group, reported recently in Phys. Rev. Lett. 91 (2003) 156401, as associated with the strongly-correlated 4f13 configuration of the Yb atom. We derived to ground-state eigenfunctions that perfectly reproduce the observed ESR values of g_perp=3.561 and g_par =0.17: 1) G_7^1 =0.803|+-3/2> +0.595|-+5/2>-0.026|-+1/2>-0.008|+-7/2> (crystal field parameters: B_2^0 = +14K, B_4^0 = +60 mK, B_6^0 = -0.5 mK, B_4^4 = -2.3 K, B_6^4 = -10 mK with a small orthorhombic distortion B_2^2 = +0.22 K, or 2) G_6^1 = 0.944|+-1/2> + 0.322|-+7/2>-0.052|-+3/2> - 0.046|+-5/2> (B_2^0 = +8 K, B_4^0 = -60 mK, B_6^0 =+6 mK, B_4^4 = -1.78 K and B_6^4 = -5 mK with a B_2^2= +0.475 K). We express our feeling that the paper of Ref. 1 will be the turning point in the heavy-fermion subject.

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arXiv2003

Crystal-field ground state for the localized f state in heavy fermion metal YbRh2Si2

We fully support the interpretation of Prof. F. Steglich, reported recently in Phys. Rev. Lett. 91 (2003)156401, that the observed \textit{below} Kondo temperature, Electron Spin Resonance (ESR) in a heavy fermion metal YbRh2Si2 is associated with the Yb3+ moment, more exactly with the strongly-correlated 4f13 configuration. We derived the ground-state eigenfunction Gamma_7^1= 0.803|\pm 3/2>+ 0.595|\mp 5/2> - 0.026|\mp 1/2> - 0.008|\pm 7/2> and crystal field parameters: B20= +14 K, B40= +60 mK, B60= -0.5 mK, B44= -2.23 K and B64= -10 mK with a small orthorhombic distortion B22= +0.23 K, that perfectly reproduce the observed ESR values of gperp= 3.561 and gpar= 0.17. These parameters also describe the observed overall temperature dependence of the paramagnetic susceptibility and predict anomalous temperature dependence of quadrupolar interactions.

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arXiv2003

Spin-orbit origin of large reduction of the effective moment in Na2V3O7*

We have shown that the observed large reduction of the effective moment and the drastic violation of the Curie-Weiss law in Na2V3O7 (Phys. Rev. Lett. 90 (2003) 167202) is caused by conventional crystal-field interactions and the intra-atomic spin-orbit coupling of the V4+ ion. The fine discrete electronic structure of the 3d1 configuration with the weakly-magnetic Kramers-doublet ground state, caused by the large orbital moment, is the reason for anomalous properties of Na2V3O7. Moreover, according to the Quantum Atomistic Solid-State Theory (QUASST) Na2V3O7 is expected to exhibit pronounced heavy-fermion phenomena at low temperatures. PACS: 71.70.E, 75.10.D Keywords: crystal-field interactions, spin-orbit coupling, orbital moment, Na2V3O7

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arXiv2003

Orbital and spin moment in CoO

The orbital and spin moment of the Co2+ ion in CoO has been calculated within the quasi-atomic approach with taking into account the intra-atomic spin-orbit coupling and crystal field interactions. The orbital moment of 1.38 m_B amounts at 0 K, in the magnetically-ordered state, to more than 34% of the total moment 4.02 m_B and yields the L/S ratio of 1.04, close to the recent experimental value. This paper has been motivated by a recent paper in Phys. Rev. B 65 (2002) 125111, in which a presented theoretical approach was unable to calculate the orbital moment. PACS No: 71.70.E; 75.10.D Keywords: crystal field, spin-orbit coupling, orbital moment, CoO

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arXiv2003

Comment on "Low-dimensional spin S=1/2 system at the quantum critical limit: Na2V3O7"

We contest the interpretation by Gavilano et al. (Phys.Rev.Lett. 90 (2003) 167202) of violation of the Curie law behavior of the paramagnetic susceptibility at low temperatures by means of the quenching of the V4+-ion moment. These results can be understood as caused by well-known conventional phenomena like crystal-field interactions but with taking into account the intra-atomic spin-orbit coupling for the V4+ ion.

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arXiv2003

A novel approach to the crystal-field theory - the orbital magnetism in 3d-ion compounds

We point out that the orbital magnetism has to be taken into account in the description of real 3d-ion compounds. According to the developed by us the Quantum-Atomistic Solid-State (QUASST) theory in compounds containing open 3d-/4f-/5f-shell atoms there exists a discrete atomic-like low-energy electronic structure that predominantly determines electronic and magnetic properties of the whole compound. The relatively weak intra-atomic spin-orbit coupling is fundamentally important as it governs the low-energy discrete electronic structure.

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arXiv2003

To the origin of large reduction of the effective moment in Na2V3O7

We have shown that the observed large reduction of the effective moment in Na2V3O7 may be caused by conventional crystal-field interactions and the intra-atomic spin-orbit coupling of the V4+ ion. The fine discrete electronic structure of the 3d1 configuration with the weakly-magnetic Kramers-doublet ground state, caused by the large orbital moment, is the reason for anomalous properties of Na2V3O7. Moreover, according to the Quantum Atomistic Solid-State Theory (QUASST), Na2V3O7 is expected to exhibit pronounced heavy-fermion phenomena at low temperatures. PACS No: 71.70.E; 75.10.D Keywords: crystal-field interactions, spin-orbit coupling, orbital moment. Na2V3O7

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arXiv2003

Orbital moment in CoO and in NiO

The total, orbital and spin moment of the Co2+ ion in CoO has been calculated within the quasi-atomic approach with taking into account strong correlations, crystal-field interactions and the intra-atomic spin-orbit coupling. The orbital moment of 1.39 μB amounts at 0 K, in the magnetically-ordered state, to more than 34% of the total moment (4.01 μB). The same calculations yield for NiO the orbital and total moment of 0.46 μB and 2.45 μB, respectively. PACS No: 71.70.E; 75.10.D Keywords: 3d magnetism, crystal field, spin-orbit coupling, orbital moment, CoO, NiO

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arXiv2003

Spin vs charge excitations in heavy-fermion compounds*

It is pointed out that the answer on the question about the role played by spin and charge excitations will help to solve the physical origin of the heavy- fermion phenomena. Our answer is that neutral spin-like excitations are responsible for the heavy-fermion phenomena whereas the role of the charge excitations is negligible. Keywords: heavy fermion, spin excitations, charge excitations PACS No: 75.20.H

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arXiv2003

Electronic structure of the V3+ ion in V2O3

We have attributed magnetism and electronic structure of V2O3 to the V3+ ions. We claim that the V3+ ion in V2O3 should be considered as described by the quantum numbers S=1 and L=3. Such quantum numbers result from two Hund's rules. The resulting electronic structure is much more complex than considered up to now, but it describes, e.g. the insulating ground state and the lowered magnetic moment, of 1.2 \muB. It turns out that the intra-atomic spin-orbit coupling is indispensable for the physically adequate description of electronic and magnetic properties of V2O3. Keywords: highly-correlated electron system, crystal field, V3+ ion, spin-orbit coupling, Mott insulators PACS: 71.70.E, 75.10.D, 75.30.Gw

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arXiv2003

The 5D term origin of the excited triplet in LaCoO3

We provide the proof for the 5D term origin of an excited triplet observed in the recent electron-spin-resonance (ESR) experiments by Noguchi et al. (Phys. Rev. B 66, 094404 (2002)). We have succeeded to fully describe experimental ESR results both for the zero-field g-factor, of 3.35, and the splitting D of 4.90 cm-1, as well as for the magnetic field applied along different crystallographic directions within the localized electron atomic-like approach as originating from excitations within the lowest triplet of the 5T2g octahedral subterm of the 5D term. In our atomic-like approach the d electrons of the Co3+ ion in LaCoO3 form the highly-correlated atomic-like 3d6 system with the singlet 1A1 ground state (an octahedral subterm of the 1I term) and the excited octahedral subterm 5T2g of the 5D term. We take the ESR experiment as confirmation of the existence of the discrete electronic structure for 3d electron states in LaCoO3 in the meV scale. PACS No: 76.30.Fc; 75.10.Dg : 73.30.-m Keywords: electronic structure, crystal field, spin-orbit coupling, LaCoO3 Submitted 24.12.2002 to Phys. Rev. B.

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arXiv2002

The orbital moment in CoO

The orbital and spin moment of the Co2+ ion in CoO has been calculated within the quasi-atomic approach with taking into account the intra-atomic spin-orbit coupling. The orbital moment of 1.38 μ_{B} amounts at 0 K, in the magnetically-ordered state, to more than 34% of the total moment (4.02 μ_{B}) and yields the L/S ratio of 1.04, close to the experimental value. PACS No: 71.70.E; 75.10.D Keywords: 3d magnetism, crystal field, spin-orbit coupling, orbital moment, CoO

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arXiv2002

The 3d-electron states in FeBr2

The fundamental controversy about the electronic structure for 3d-electron states in FeBr2 is discussed. We advocate for the localized electron atomic-like many-electron crystal-field approach that yields the discrete energy spectrum, in the scale of 1 meV, associated with the atomic-like states of the Fe2+ ions in contrary to the (semi-)continuous energy spectrum yielded by band theories. In our approach the six d electrons of the Fe2+ ion form the highly-correlated atomic-like electron system 3d6 described by two Hund's rules quantum numbers S=2 and L=2 with taking into account the spin-orbit coupling. The superiority of our model relies in the fact that it explains consistently properties of FeBr2, the insulating and the magnetic ground state as well as thermodynamics and Raman low-energy spectra, using well-established physical concepts. Keywords: 3d magnetism, Hund's rules, spin-orbit coupling, crystal field, FeBr2 PACS: No: 75.50.Ee : 71.15.Mb

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arXiv2002

The 3d-electron states in LaMnO3*

Three fundamentally different electronic structures for 3d electron states in LaMnO3, discussed in the current literature, have been presented. We are in favour of the localized electron atomic-like crystal-field approach that yields the discrete energy spectrum, in the scale of 1 meV, associated with the atomic-like states of the Mn3+ ions in contrary to the continuous energy spectrum yielded by band theories. In our atomic-like approach the d electrons form the highly-correlated electron system 3d4 described by two Hund's rules quantum numbers S=2 and L=2. We take into account the spin-orbit coupling, Jahn-Teller distortion and formation of the magnetic state. The resulting electronic structure is completely different from that presented in the current literature. The superiority of our model relies in the fact that it explains consistently properties of LaMnO3, the insulating and magnetic ground state and thermodynamics, using well-established physical concepts. Keywords: 3d magnetism, Hund's rules, spin-orbit coupling, crystal field, LaMnO3 PACS: No: 71.70.Ej : 75.10.Dg : 73.30.-m

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arXiv2002

Influence of spin-orbit interactions on the cubic crystal-field states of the d4 system*

It has been shown that for the highly-correlated d4 electronic system the spin-orbit interactions produce, even in case of the cubic crystal-field interactions, a singlet ground state. Its magnetic moment grows rapidly with the applied magnetic field approaching 4 uB for the Eg state, but only 3 uB for the T2g state. The applicability of the present results to the Mn3+ ion in LaMnO3 is discussed. Keywords: crystal-field, spin-orbit, orbital moment. PACS: 71.70.E, 75.10.D

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