A novel approach to the crystal-field theory – the orbital magnetism in 3d-ion compounds
R. J. Radwanski∗
Center of Solid State Physics; Snt. Filip 5, 31-150 Krakow, Poland
Institute of Physics, Pedagogical University, 30-084 Krakow, Poland
Z. Ropka
Center of Solid State Physics; Snt. Filip 5, 31-150 Krakow, Poland
(12.07.2001, cond-mat/0307575 23 July 2003, published 29 December 2006)
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.
PACS: 75.10.Dg; 71.70.Ch
Keywords: crystal field, spin-orbit coupling, orbital magnetism
The Jahn-Teller theorem for the 3d magnetic ions
Z. Ropka
Center of Solid State Physics; SntFilip 5, 31-150 Krakow, Poland
R. J. Radwanski∗
Center of Solid State Physics; SntFilip 5, 31-150 Krakow, Poland
Institute of Physics, Pedagogical University, 30-084 Krakow, Poland
(PRL 16.02.1999, cond-mat/0006231 14 Jun 2000, published 29 December 2006)
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.
PACS: 71.70.Ej; 75.10.Dg;
Keywords: Jahn-Teller theorem, spin-orbit coupling
Formation of the heavy-fermion state – an explanation in a model traditionally called localized♠
R. J. Radwanski∗
Center of Solid State Physics; SntFilip 5, 31-150 Krakow, Poland
(SCES-92, cond-mat/9906287 17 Jun 1999, published 29 December 2006)
In contrary to widely spread view about the substantial delocalization of f electrons in heavy-fermion (h-f) compounds it is argued that h-f phenomena can be understood with localized f electrons. Then the role of crystal-field interactions is essential and the heavy-fermion behaviour can occur for the localized Kramers-doublet ground state.
PACS: 75.20.Hr; 75.10.Dg
Keywords: heavy-fermion, crystal-field, Kramers-doublet
Giant Sommerfeld coefficient in the heavy-fermion YbBiPt
Z. Ropka∗
Center of Solid State Physics; SntFilip 5, 31-150 Krakow, Poland
(PRL-30-12-1999, cond-mat/0005363 22 May 2000, published 29 December 2006)
It has been derived that the Sommerfeld coefficient γ as large as 25 J/K2mol can be theoretically accounted for provided the charge f-electron fluctuations are substantially suppressed. This result enables the understanding of the heavy-fermion YbBiPt (γ =8 J/K2mol) as the spin fluctuator and should stimulate the experimental specific-heat
research at low temperatures.
PACS: 71.28.+d; 65.20.+w
Keywords: strongly-correlated electron systems, heavy-fermion systems, YbBiPt
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Spin vs charge excitations in heavy-fermion compounds♠
R. J. Radwanski∗
Center of Solid State Physics; Snt. Filip Street 5, 31-150 Krakow, Poland
Institute of Physics, Pedagogical University, 30-084 Krakow, Poland
Z. Ropka
Center of Solid State Physics; Snt. Filip Street 5, 31-150 Krakow, Poland
(SCES-02, cond-mat/0303321 17 March 2003, published 29 December 2006)
Keywords: heavy fermion, spin excitations, charge excitations
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NiO – from first principles♠
R. J. Radwanski∗
Center of Solid State Physics; SntFilip 5, 31-150 Krakow, Poland
Institute of Physics, Pedagogical University, 30-084 Krakow, Poland
Z. Ropka
Center of Solid State Physics; SntFilip 5, 31-150 Krakow, Poland
(PRL 19.06.2006, cond-mat/0606604 23 Jun 2006, published 29 December 2006)
We have calculated from first-principles the octupolar interactions of the Ni2+ ion in NiO, which gives the theoretical basis for the ionic description of properties of NiO with fully localized strongly-correlated eight d electrons. A failure of the up-now first principles ionic calculations for NiO was largely due to too small values taken for the octupolar moment of the transition-metal atom, largely generated by too small value for r4d. Our many-electron crystal-field based approach enables successful calculations of the electronic structure and magnetic properties both in the paramagnetic and in magnetically-ordered state as well as zero-temperature properties and thermodynamics.
PACS: 71.10.-w; 75.10.Dg
Keywords: electronic structure, crystal field, spin-orbit coupling, NiO
The quantum atomistic solid-state theory♠
R. J. Radwanski∗
Center of Solid State Physics; SntFilip 5, 31-150 Krakow, Poland
Institute of Physics, Pedagogical University, 30-084 Krakow, Poland
Z. Ropka
Center of Solid State Physics; SntFilip 5, 31-150 Krakow, Poland
(PRL 16.02.1999; PRL 18.09.2000; cond-mat/0010081 5 October 2000, PRB 20.07.2001; under the law protection of PRL, PRB (1 million USD scientific bet) and the President of the American Phys. Society; published 29 January 2007)
The quantum atomistic solid-state theory (QUASST) is developed for compounds containing open-shell 3d, 4f and 5f atoms and points out the existence in a solid of the atomic-like discrete electronic structure determined by the crystal-field and spin-orbit interactions. These low energy localized states determine electronic and magnetic properties
of 3d/4f/5f atom containing compounds. QUASST accounts for very strong correlations within 3d/4f/5f electrons. QUASST unifies the description of 3d/4f/5f atoms and their compounds and allows to bridge the atomic physics and the solid-state physics.
PACS: 71.10.-w; 75.10.-b;
Keywords: strong electron correlations, 4f compounds, 3d compounds, crystal field, spin orbit coupling
Are there crystal field levels in UPd2Al3? We answer, THERE ARE♠
R. J. Radwanski∗
Center of Solid State Physics; SntFilip 5, 31-150 Krakow, Poland
Institute of Physics, Pedagogical University, 30-084 Krakow, Poland
Z. Ropka
Center of Solid State Physics; SntFilip 5, 31-150 Krakow, Poland
(cond-mat/0412257 19 December 2004, published 29 January 2007)
We claim that crystal field (CEF) levels exist in UPd2Al3 in contrary to a recent claim of Hiess et al. (cond-mat/0411041) and Bernhoeft et al. (cond-mat/0411042), that there is no experimental evidence for discrete crystal field levels in this superconducting heavy-fermion antiferromagnet. We claim that excitations revealed by Krimmel et al. (J. Phys.: Condens. Matter 8 (1996) 1677) in inelastic-neutron- scattering (INS) studies are i) crystal-field excitations described by us within ii) the 5f 3 (U3+) configuration. Moreover, our 5f 3 (U3+) scheme, presented in Physica B 276-278 (2000) 803 and in Czech. J. Phys. 54 (2004) D295, provides a clear physical explanation for the 1.7 meV excitation (magnetic exciton) as associated to the removal of the Kramers-doublet ground state degeneracy in the antiferromagnetic state. The crystal-field theory completed by strong intra-atomic correlations and intersite spin-dependent interactions to the Quantum Atomistic Solid State Theory (QUASST), offers the meV energy scale needed for description of magnetic and electronic properties of compounds containing open-shell 3d, 4f , 5f atoms. The derived set of CEF parameters for the U3+ state reproduces both the INS excitations, temperature dependence of the heat capacity, large uranium magnetic moment as well as its direction.
PACS: 71.70.Ej; 75.10.Dq
Keywords: Crystalline Electric Field, 5f compounds, Heavy fermion, magnetism, UPd2Al3
Comment on a Phys. Rev. Lett. paper: ”Nanomagnetic droplets and implications to orbital ordering in La1−xSrxCoO3”: the origin of the excited state in LaCoO3
R. J. Radwanski∗
Center of Solid State Physics; SntFilip 5, 31-150 Krakow, Poland
Institute of Physics, Pedagogical University, 30-084 Krakow, Poland
Z. Ropka
Center of Solid State Physics; SntFilip 5, 31-150 Krakow, Poland
(PRL 28.03.2006; cond-mat/0603812 30 March 2006, published 29 January 2007)
In contrary to a claim of the recent Phys. Rev. Lett. 96 (2006) 027201 paper we maintain that the first excited state in LaCoO3 is the high-spin (HS) state (a lowest quasi-triplet from the octahedral subterm 5T2g of the 5D term, Phys. Rev. B 67 (2003) 172401) in agreement with the Tanabe-Sugano diagram.
PACS: 75.10.Dg; 71.70.Ch;
Keywords: 3d compounds, electronic structure, crystal field, spin-orbit coupling, LaCoO3
The 3d-electron states in FeBr2♠
R. J. Radwanski∗
Center of Solid State Physics; SntFilip 5, 31-150 Krakow, Poland
Institute of Physics, Pedagogical University, 30-084 Krakow, Poland
Z. Ropka
Center of Solid State Physics; SntFilip 5, 31-150 Krakow, Poland
(PRB 18.06.2002 BT8231, cond-mat/0211657 28 November 2002, published 29 January 2007)
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 provided by band theories. In our approach the six d electrons of the Fe2+ ion in FeBr2 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.
PACS: 71.10.-w; 75.10.-b; 75.10.Dg
Keywords: 3d magnetism, 3d compounds, Hund’s rules, spin-orbit coupling, crystal field, FeBr2
30 lat zjawisk ciężko-fermionowych: czy już wiemy, które elektrony są silnie skorelowane♠
R. J. Radwanski∗
Instytut Fizyki Akademii Pedagogicznej, ul. Podchorążych 2, 30-084 Kraków
Centrum Fizyki Ciała Stałego, ul. Św. Filipa 5, 31-150 Kraków
Z. Ropka
Centrum Fizyki Ciała Stałego, ul. Św. Filipa 5, 31-150 Kraków
Keywords: heavy fermion, spin excitations, charge excitations
Introduction to rare-earth compounds. Magnetism and electronic structure of PrNi5 and ErNi5
R. J. Radwanski∗
Center of Solid State Physics; Snt. Filip 5, 31-150 Krakow, Poland
Institute of Physics, Pedagogical University, 30-084 Krakow, Poland
Z. Ropka
Center of Solid State Physics; Snt. Filip 5, 31-150 Krakow, Poland
(prepared for Workshop ”Neutron Scattering in Novel Materials, August 5-11, 2000, organized by Prof. Albert Furrer, ETH Zurich and PSI, Switzerland, see also Physica B 319 (2002) 78; published 28 February 2007)
The basic concepts of the crystal-field theory and its application to rare-earth compounds have been presented. Very consistent physical understanding of electronic, magnetic and spectroscopic properties of PrNi5 and ErNi5 has been obtained treating the RE atoms as highly- correlated electron systems. The fine electronic structure, related with the atomic-like states and determined by the crystal-field and spin-orbit interactions, has been evaluated by means of different experimental techniques. The importance of the higher-order charge multipolar interactions and the local symmetry of the crystal field for the realized fine electronic structure and for the ground state are pointed out. We pointed out that significant successes of the crystal-field theory indicate on the substantial preservation of the atomic-like structure of the open- shell atoms even when they become the part of a solid. An extension of the CEF theory to a quantum atomistic solid-state theory is proposed.
PACS: 71.10.-w; 75.10.-b;
Keywords: strong electron correlations, 4f compounds, 3d compounds, crystal field, spin orbit coupling
Magnetic properties and the electronic structure of LiCoO2♠
R. J. Radwanski∗
Center of Solid State Physics; Snt. Filip 5, 31-150 Krakow, Poland
Institute of Physics, Pedagogical University, 30-084 Krakow, Poland
Z. Ropka
Center of Solid State Physics; Snt. Filip 5, 31-150 Krakow, Poland
(submitted to the SCTE-06 Conference (Krakow, Prof. A. Szytula) 31 May 2006; cond-mat/0610611 23 October 2006, published 28 February 2007)
We have described properties of LiCoO2 within the Quantum Atomistic Solid State (QUASST) theory taking into account very strong electron correlations, predominantly of the intra-atomic origin, spin-orbit coupling and the detailed local crystallographic surroundings and its symmetry. Properties of LiCoO2 are consistently explained together with NaCoO2 and LaCoO3 – in all of these compounds the Co3+ ions occur in the low-spin state. This low-spin state is the effect of the relatively strong crystal-field interactions (Bz = +320 K ⇐⇒ 10Dq = 3.3 eV) and is a manifestation of the very large orbital moment of the Co3+ ion.
PACS: 71.10.-w; 75.10.Dg
Keywords: 3d compounds, electronic structure, crystal field, spin-orbit coupling, LiCoO2
Comment on Phys. Rev. Lett. ”All-Electron Self-Consistent GW Approximation: Application to Si, MnO, and NiO”. Magnetic moment of NiO
R. J. Radwanski∗
Center of Solid State Physics; Snt. Filip 5, 31-150 Krakow, Poland
Institute of Physics, Pedagogical University, 30-084 Krakow, Poland
Z. Ropka
Center of Solid State Physics; Snt. Filip 5, 31-150 Krakow, Poland
(Phys. Rev. Lett. 28 November 2005 (LLK 1033); cond-mat/0511624 25 November 2005, published 28 February 2007)
By this Comment we would like to express our deep scepticism about ”Excellent agreement with experiment for many properties” of NiO claimed in the abstract of a paper in Phys. Rev. Lett. 93, 126406 (2004) by Faleev et al. [1] which has been obtained with ”a new kind of self-consistent GW (SCGW) approximation based on the all-electron, full potential linear muffin-tin orbital method.”
PACS: 71.10.-w; 75.10.-b
Keywords: strong electron correlations, 3d compounds, crystal field, spin orbit coupling
Comment on Phys. Rev. Lett.’s paper ”All-Electron Self-Consistent GW Approximation: Application to Si, MnO, and NiO”: band vs localized description of NiO
R. J. Radwanski∗
Center of Solid State Physics; Snt. Filip 5, 31-150 Krakow, Poland
Institute of Physics, Pedagogical University, 30-084 Krakow, Poland
Z. Ropka
Center of Solid State Physics; Snt. Filip 5, 31-150 Krakow, Poland
(Phys. Rev. Lett. 11 December 2006 (LZK 1009); cond-mat/0605567 23 May 2006, published 28 February 2007)
By this Comment we would like to express our large disagreement about a conclusive statement of a paper [1] in Phys. Rev. Lett. 93, 126406 (2004) that authors Faleev, van Schilfgaarde, and Kotani ”believe that the band picture [23, here Ref. [2]] for NiO is a reasonable starting point for the description of the electronic structure of NiO, much better than previously thought, and in many respects more appropriate than the ligand-field picture.” Faleev et al. [1] have performed electronic-structure calculations with ”a new kind of self-consistent GW (SCGW) approximation based on the all-electron, full potential linear muffin-tin orbital method.” getting continuous energy spectrum, a band of d electrons wide by 5-6 eV with a spin-polarization of eg–eg states by 2-3 eV similar to that got by Terakura et al. [3, 8]. In contrary to authors of Ref. [1] we argue that the many-electron crystal-field approach, known from works of Bethe and Van Vleck from 1929 with predominantly Ni2+ and O2− ions, is physically adequate jtarting point for discussion of the electronic structure and magnetism of NiO [3, 4, 6]. Being mofv exact, we claim that the continuous electronic structure for d electrons presented in Figs 2 and 3 of Ref. [1] is not realized in the reality – we claim that in NiO exists the discrete electronic structure.
PACS: 71.10.-w; 75.10.-b
Keywords: strong electron correlations, 3d compounds, crystal field, spin orbit coupling
Czyżby w CeRhSb nie było stanów pola krystalicznego, jeżeli są np. w CePdSb?♠
R. J. Radwanski∗
Instytut Fizyki Akademii Pedagogicznej, ul. Podchorążych 2, 30-084 Kraków
Centrum Fizyki Ciała Stałego, ul. Św. Filipa 5, 31-150 Kraków
Z. Ropka
Centrum Fizyki Ciała Stałego, ul. Św. Filipa 5, 31-150 Kraków
XII Krajowa Szkoła Nadprzewodnictwa:
“Układy skorelowanych elektronów wczoraj i dziś”, Ustroń 14-18 IX 2006 ABSTRACT, 31 Lipiec 2006
Słowa kluczowe: pole krystaliczne, silne korelacje elektronowe, CeRhSb, CePdSb
Stan podstawowy jonu Mn3+ w LaMnO3 – 5Eg czy t2g3eg1?♠
Z. Ropka
Centrum Fizyki Ciała Stałego, ul. Św. Filipa 5, 31-150 Kraków
R. J. Radwanski∗
Centrum Fizyki Ciała Stałego, ul. Św. Filipa 5, 31-150 Kraków
Instytut Fizyki Akademii Pedagogicznej, ul. Podchorążych 2, 30-084 Kraków
LaMnO3 jest materiałem z potencjalnym zastosowaniem w spintronice po częściowej podmianie atomów La atomami Ca lub Sr. Te podstawienia prowadzą do stanu ferromagnetycznego i co ważne do wzrostu temperatury magnetycznego uporządkowania w pobliże temperatury pokojowej co umożliwia praktyczne zastosowanie. Stan podstawowy jest / był przedmiotem długotrwałych kontrowersji. Wyniki naszych obliczeń, potwierdzających wcześniejsze obliczenia z teorii pola krystalicznego, o stanie 5Eg jako stanie podstawowym jonu Mn3+ w LaMnO3 nie uzyskały uznania w 2002 roku. Oponenci podnosili, że inni autorzy podają stan podstawowy jako t2g3eg1, zaś stan t2g jako najniższy i eg jako leżący powyżej.
Słowa kluczowe: silne korelacje elektronowe, pole krystaliczne, moment orbitalny, LaMnO3
Magnetism of FeO from first principles atomistic ab initio calculations
R. J. Radwanski∗
Center of Solid State Physics; Snt. Filip 5, 31-150 Krakow, Poland
Institute of Physics, Pedagogical University, 30-084 Krakow, Poland
Z. Ropka
Center of Solid State Physics; Snt. Filip 5, 31-150 Krakow, Poland
(Phys. Rev. Lett. LB11267, 16 February 2007; published 30 March 2007)
We have calculated from first-principles the octupolar interactions of the Fe2+ ion in FeO, which gives the theoretical basis for the ionic description of properties of FeO with fully localized six strongly- correlated d electrons. A failure of the up-now first principles ionic calculations for FeO was largely due to too small values taken for the octupolar moment of the transition-metal atom, largely generated by too small value for (r4). Our many-electron crystal-field based approach enables successful calculations of the electronic structure and magnetic properties both in the paramagnetic and in magnetically-ordered state as well as zero-temperature properties and thermodynamics. Our approach reveals importance of the spin-orbit coupling for calculations of the magnetism and electronic structure of 3d oxides.
PACS: 71.10.-w; 75.10.Dg
Keywords: 3d oxides, electronic structure, crystal field, spin-orbit coupling, FeO
On the crystal field in the modern solid-state theory♠
R. J. Radwanski∗
Center of Solid State Physics; Snt. Filip 5, 31-150 Krakow, Poland
Institute of Physics, Pedagogical University, 30-084 Krakow, Poland
Z. Ropka
Center of Solid State Physics; Snt. Filip 5, 31-150 Krakow, Poland
(cond-mat/0504199, 8 April 2005; published 30 March 2007)
We point out the high physical correctness of the use and the concept of the crystal-field approach, even if is used to metallic magnetic materials of transition-metal 3d/4f/5f compounds. We discuss the place of the crystal-field theory in modern solid-state physics and we point out the necessity to consider the crystal-field approach with the spin-orbit coupling and strong electron correlations, as a contrast to the single-electron version of the crystal field customarily used for 3d electrons. We have extended the strongly-correlated crystal-field theory to a Quantum Atomistic Solid-State Theory (QUASST) to account for the translational symmetry and inter-site spin-dependent interactions indispensable for formation of magnetically-ordered state. We have correlated macroscopic magnetic and electronic properties with the atomic-scale electronic structure for ErNi5, UPd2Al3, FeBr2, LaCoO3 and LaMnO3. In QUASST we have made unification of 3d and rare-earth compounds in description of the low-energy electronic structures and magnetism of open 3d-/4f-/5f-shell electrons. QUASST offers consistent description of zero-temperature properties and ther- modynamic properties of 4f-/5f-/3d-atom containing compounds. Our studies indicate that it is the highest time to unquench the orbital magnetism in 3d oxides.
PACS: 71.70.Ch, 75.10.-b
Keywords: Crystal Field, spin-orbit coupling, Heavy fermion, magnetism, 3d oxides
Role of f electrons in rare-earth and uranium intermetallics – an alternative look at heavy-fermion phenomena.
R. J. Radwanski∗
Center of Solid State Physics; SntFilip 5, 31-150 Krakow, Poland
(cond-mat/9911292, 18 November 1999; published 30 March 2007)
PACS: 75.10.-b, 71.70.Ch
Keywords: Heavy fermion, Crystal Field, spin-orbit coupling, magnetism, 5f compounds
Electronic structure of LaMnO3 and magnetocaloric effects
R. J. Radwanski∗
Center of Solid State Physics; Snt. Filip 5, 31-150 Krakow, Poland
Institute of Physics, Pedagogical University, 30-084 Krakow, Poland
Z. Ropka
Center of Solid State Physics; Snt. Filip 5, 31-150 Krakow, Poland
For understanding of electronic, magnetic and transport properties of Sr/Ca doped LaMnO3 it is of fundamental importance to know the electronic structure of the maternal stoichiometric compound. Despite of very extensive theoretical studies the consensus about the electronic structure of LaMnO3 is not reached yet. In the current literature there are electronic structures with continuous energy spectrum for d electrons as well as with a discrete energy spectrum, with completely different ground state. We advocate for the existence in LaMnO3 the discrete electronic structure related to the Mn3+ ion in LaMnO3 with the 5Eg octahedral subterm as the ground state (Physica B 281-282 (2000) 507; cond-mat/0211595) – such the ground state is, however, questioned, to our big surprise, by the magnetic community, recently by the Scientific Committee of the Strongly-Correlated Electron System Conference SCES-02 [OO015PO]. We hope that the present Conference provides a good scientific forum for the open discussion of the electronic structure of the stoichiometric LaMnO3. We point out that the desired properties of manganites result from strong correlations among d electrons, where the relativistic spin-orbit coupling and the local symmetry (Jahn-Teller effect) at the Mn site play fundamentally important role.
Monooxides NiO, CoO and FeO solved!
R. J. Radwanski∗
Center of Solid State Physics; Snt. Filip 5, 31-150 Krakow, Poland
Institute of Physics, Pedagogical University, 30-084 Krakow, Poland
Z. Ropka
Center of Solid State Physics; Snt. Filip 5, 31-150 Krakow, Poland
(published 30 April 2007; online: www.actaphysica.eu)
We have solved a problem of the magnetism and the insulating ground state of monooxides NiO, CoO and FeO. Our many-electron crystal-field based approach enables successful calculations of the electronic structure and magnetic properties both in the paramagnetic and in the magnetically-ordered state as well as zero-temperature properties and thermodynamics. Our approach is within the strong electron correlations and the strong hybridization limit and the electronic structure is evaluated in the meV scale.
PACS: 71.10.-w; 75.10.Dg
Keywords: 3d oxides, electronic structure, crystal field, spin-orbit coupling, NiO, CoO, FeO
Crystal field, spin-orbit coupling and magnetism in a ferromagnet YTiO3♠
R. J. Radwanski∗
Center of Solid State Physics; Snt. Filip 5, 31-150 Krakow, Poland
Institute of Physics, Pedagogical University, 30-084 Krakow, Poland
Z. Ropka
Center of Solid State Physics; Snt. Filip 5, 31-150 Krakow, Poland
(cond-mat/0601005, 2 January 2006; under the author’s right protection of the American Physical Society from January 4, 2006 (Phys. Rev. Lett. LN10075) published 30 April 2007; online: www.actaphysica.eu)
Magnetic properties of stechiometric YTiO3 has been calculated within the single-ion-based paradigm taking into account the low- symmetry crystal field and the intra-atomic spin-orbit coupling of the Ti3+ ion. Despite of the very simplified approach the calculations reproduce perfectly the value of the magnetic moment and its direction as well as temperature dependence of the magnetic susceptibility χ(T ). It turns out that the spin-orbit coupling is fundamentally important for 3d magnetism and magnetic properties are determined by lattice distortions.
PACS: 75.10.Dg, 75.25.+z
Keywords: Crystalline Electric Field, 3d oxides, magnetism, spin-orbit coupling, YTiO3
The low-energy electronic structure and the orbital magnetism in NiO♠
R. J. Radwanski∗
Center of Solid State Physics; Snt. Filip 5, 31-150 Krakow, Poland
Institute of Physics, Pedagogical University, 30-084 Krakow, Poland
Z. Ropka
Center of Solid State Physics; Snt. Filip 5, 31-150 Krakow, Poland
(cond-mat/0412484 17 December 2004, under the author’s right protection of the American Physical Society from July 11, 2001 (Phys. Rev. B BG8156); published 30 April 2007; online: www.actaphysica.eu)
The orbital and spin moment of the Ni2+ ion in NiO has been calculated within the quasi-atomic approach. The orbital moment of 0.46 μB amounts at 0 K, in the magnetically-ordered state, to about 20% of the total moment (2.45 μB). For this outcome, being in nice agreement with the recent experimental finding of the orbital moment, taking into account the intra-atomic spin-orbit coupling is indispensable.
PACS: 71.10.-w, 75.10.-b
Keywords: Crystalline Electric Field, 3d oxides, orbital moment, magnetism, NiO
Crystal-field states in NaCoO2 and in wet cobalt superconductors (NaxCoO2)♠
R. J. Radwanski∗
Center of Solid State Physics; Snt. Filip 5, 31-150 Krakow, Poland
Institute of Physics, Pedagogical University, 30-084 Krakow, Poland
Z. Ropka
Center of Solid State Physics; Snt. Filip 5, 31-150 Krakow, Poland
(cond-mat/0602592, 24 February 2006; published 30 April 2007; online: www.actaphysica.eu)
We claim that for calculations of the electronic structure of 3d oxides very strong electron correlations have to be taken into account similarly to those assumed in many-electron crystal field approach. For Co3+ ions in NaxCoO2 yH2O there are 15 low lying many-electron states within 0.1 eV as can be obtained in the many-electron CEF approach with taking into account the spin-orbit coupling. We claim, that the used by us Hamiltonian for the trigonal distortion is correct.
PACS: 75.10.Dg, 71.70
Keywords: crystal field, 3d oxides, magnetism, spin-orbit coupling, NaCoO2
Comment on a Phys. Rev. Lett. paper ”Spin State Transition in LaCoO3 studied using Soft X-ray absorption spectroscopy and Magnetic Circular Dichroism”: physics of LS, IS and HS spin states
R. J. Radwanski∗
Center of Solid State Physics; Snt. Filip Street 5, 31-150 Krakow, Poland
Institute of Physics, Pedagogical University, 30-084 Krakow, Poland
Z. Ropka
Center of Solid State Physics; Snt. Filip Street 5, 31-150 Krakow, Poland
(under the author’s right protection of the American Physical Society from January 3, 2007 (Phys. Rev. Lett. LAK1030) published 30 April 2007; online: www.actaphysica.eu)
We argue that the energy level diagram of a CoO6 cluster presented in Fig. 2 in the recent Phys. Rev. Lett. 97 (2006) 176405 paper is physically inadequate to LaCoO3 and that the description of the HS, IS and LS spin states in LaCoO3 is oversimplified.
PACS: 75.10.Dg : 71.70.
Keywords: spin states, crystal field, LaCoO3, 3d compounds
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PHYSICS OF HEAVY-FERMION SYSTEMS*
R. J. Radwanski∗
Center of Solid State Physics; Snt. Filip 5, 31-150 Krakow, Poland
Institute of Physics, Pedagogical University, 30-084 Krakow, Poland
(reprint of Report of the Center of Solid State Physics, Krakow, CSSP-4/95 (1995); under law protection of Polish Academy of Sciences and Minister of Science (1995); published 31 July 2007; online: www.actaphysica.eu)
A B S T R A C T
The understanding of conventional rare-earth intermetallic compounds is summarized by analysis of magnetic and electronic properties of conventional rare-earth intermetallic compounds. Conventional rare-earth compounds are understood well within the individualized-electron model in which f electrons are keeping their individuality also being part of the compound. In intermetallics there coexist itinerant/band electrons as well as localized f electrons which form a highly correlated electronic subsystem f n. The analysis gives a clear evidence that the localized f electrons provide a substantial contribution to the specific heat, with the entropy of R ln2 in the case of Kramers ions. The f specific heat is extraordinarily large at lowest temperatures if the Kramers doublet ground state of the f subsystem is only slightly split. Such situation is supposed to occur in compounds exhibiting heavy-fermion phenomena. The heavy-fermion behavior is related to difficulties in the removal of the Kramers degeneracy of the f n electronic subsystems that results in the small energy splitting δ. The removal of the Kramers degeneracy, that has to occur before the system reaches the absolute zero temperature, causes the appearance of two-closely-lying localized states with oppositely oriented local magnetic moments. Thermal excitations over the energy gap δ, that can be of order of 0.1 meV, cause the reversal of the local magnetic moment and subsequently pulls the reversal of the oscillatory spin polarization of conduction electrons. This complex object of the localized Kramers fermion with bounded conduction electrons can be regarded as a quasiparticle exhibiting bozonic properties. In this view, the heavy-fermion state is a magnetic, spin-wave state which is formed after breaking of the time- reversal symmetry. The splitting δ and the separation to the first excited CEF level Δ introduce two energy scales. Δ seems to be associated with the temperature denoted often as the Kondo temperature whereas δ – with the width of the Kondo resonance thought to be at the Fermi level within the Fermi-liquid model. Two energy scales appeal from many experimental data.