Concentration model of semiconductor-metal phase transitions in SmS

Каминский, В. В.; Vasil’ev, L. N.

doi:10.1134/s1063783408040197

Cited by 5 publications

(7 citation statements)

References 2 publications

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“…In this Brief Report we show that this exchange interaction may cause formation of the magneticpolaron ͑MP͒ bound state in SmS with a characteristic radius of about 0.5 nm, as required to both reconcile the results of Ref. 9 with the experiment and support the idea of a hypothetical bound state invoked to describe the mysterious MV phase for pressures between p BG and p ⌬ .…”

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confidence: 74%

“…17 Since the positive muon 26 and the Sm 3+ ion 15 both adopt an interstitial position in SmS, the observed MP may serve as a model for the hypothetical bound state around native Sm 3+ ions proposed 8 to account for MV behavior in SmS. Furthermore, since the 4f electron is strongly ͑0.03 nm͒ localized, 9,14 radius a B of a bound state at a Mott-type MIT under pressure can be roughly estimated from a B ϫ n k 1/3 Ϸ 0.2-0.4 giving a B Ϸ 0.25-0.45 nm, since n k Ϸ 8 ϫ 10 19 cm −3 in SmS at 300 K at MIT. 14 This value is consistent with R Ϸ 0.5 nm found for the MP bound to the muon in SmS.…”

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confidence: 95%

“…7 In the black phase, the Fermi level E F falls into a gap between a 4f 6 level and an unoccupied 5d band, thus making Sm 2+ S 2− a nonmagnetic narrow-gap semiconductor. 8 In the golden phase, the 4f 6 level may be pushed into the conduction band, 8,9 resulting in a mix of divalent 4f 6 and trivalent 4f 5 configurations. In this phase the high-temperature resistivity is metallic but at low temperature the ground state is a strongly correlated semiconductor as long as the pressure is lower than p ⌬ Ϸ 2 GPa.…”

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Magnetic polaron bound to the positive muon in SmS: Exchange-driven formation of a mixed-valence state

et al. 2009

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Muon spin-rotation experiments ͑supported by magnetization measurements͒ have been carried out in the canonical 4f mixed-valence narrow-gap semiconductor SmS from 10 to 900 K in magnetic fields up to 3.5 T. A bound state of an electron around a positive muon is found to form up to about 800 K. This state is a magnetic polaron: the electron wave function is confined within R Ϸ 0.5 nm ͑the first two coordination spheres͒ due to its exchange interaction with Sm magnetic moments. As such, it may serve as a model system for the hypothetical bound state suggested to account for a transition from divalent Sm 2+ to trivalent Sm 3+ , which is invoked to explain the transformation of SmS from a paramagnetic insulator into a magnetic metal at high pressure.The problem of spin and charge fluctuations close to a magnetic instability in mixed-valence ͑MV͒ systems has attracted considerable attention ͑see, e.g., Ref. 1 and references therein͒. In strongly correlated 4f electron systems, the class of MV materials known as narrow-gap semiconductors or Kondo insulators ͑SmB 6 , YbB 12 , TmSe, etc.͒ supports hybridization between localized 4f states and itinerant 5d-6s states causing instabilities in charge and magnetic configurations. These materials have been studied for almost four decades 2 but the mechanism of the valence fluctuation remains mysterious. Among them, the canonical MV system SmS makes an ideal material in which to study charge fluctuations in the vicinity of a quantum critical point because of the relative ease with which the Sm ion changes its ion charge state. Although a consensus has been reached that the remarkable properties of SmS may be understood in terms of a Sm 2+ ͑4f 6 ; J =0͒ → Sm 3+ ͑4f 5 ; J =5/ 2͒ + e͑d , s͒ transition, 3 the mechanism of the electron capture/release remains a subject of current interest.Unlike classical magnetic semiconductors ͑Eu chalcogenides, magnetic spinels, etc.͒ which experience metalinsulator transitions ͑MIT͒ close to the magnetic ordering temperature 4,5 at ambient pressure SmS remains a paramagnetic semiconductor within a NaCl crystal structure down to low temperature. 2 As the pressure is increased, SmS exhibits two successive phase transitions. First it undergoes an isostructural transition at the remarkably low pressure of p BG Ϸ 0.65 GPa ͑at room temperature͒, 6 involving a valence change from a Sm 2+ to a homogeneous mixed-valent ͑2.6-2.8͒ state. 2 This first-order phase transition is characterized by a huge volume collapse of up to 15% accompanied by a color change from black to golden. 7 In the black phase, the Fermi level E F falls into a gap between a 4f 6 level and an unoccupied 5d band, thus making Sm 2+ S 2− a nonmagnetic narrow-gap semiconductor. 8 In the golden phase, the 4f 6 level may be pushed into the conduction band, 8,9 resulting in a mix of divalent 4f 6 and trivalent 4f 5 configurations. In this phase the high-temperature resistivity is metallic but at low temperature the ground state is a strongly correlated semiconductor as long as the pressure i...

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Magnetic polaron bound to the positive muon in SmS: Exchange-driven formation of a mixed-valence state

et al. 2009

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“…Point defects have a great influence on electrical properties of SmS whose concentration can reach to ~ 10 21 сm -3 due to wide zone of compound homogeneity displaced to direction of the samarium surplus. Accordingly to the researches [3,5,8] in crystals with samarium surplus the dominant defects are antisite samarium SmS atoms that form shallow donor levels with ionization energy 0,045eV in crystal band gap. Also sulphur vacancies can be formed in samarium monosulphide [6], that are considered to be shallow acceptors accordingly to [7].…”

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Thermodynamics of the Point Defects in the Metallic Phase of the Samarium Monosulphide

Gorichok

Shevchuk

Boychuk

2016

jpnu

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Abstract.The equilibrial values of the vacancy concentration of chalcogen and antistructural samarium atoms in metallic phase of SmS were calculated by minimization the crystal thermodynamic potential. It was determined that the dominant defects are + at the concentration of samarium 50,5-54 at. % and at the temperature of T=300-400 K. Also the concentration of negatively charged sulfur vacancies − is less on 1-2 points. The concentric dependence of samarium monosulphide density was explained using this offered model.

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“…The width of the gap (E g ) between the valence and conductivity bands in SmS is somewhat smaller compared to MnS. Under the external pressure P $ 6.5 kbar, the SmS lattice is abruptly compressed and the lattice parameter reaches the value a p ¼ 0.569 nm; resistivity decreases by an order of magnitude; volume, by 13%; and magnetic susceptibility, by 60% [9][10][11]. The authors of Ref.…”

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Magnetic properties of Sm_xMn_1−xS solid solutions

Aplesnin

Романова

Ryabinkina

et al. 2011

Physica Status Solidi (b)

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The structural and magnetic properties of Sm x Mn 1Àx S (0.01 x 0.2) solid solutions synthesized on the basis of an antiferromagnetic semiconductor a-MnS are experimentally studied in the temperature range 4.2-300 K in magnetic fields up to 9 T. The magnetic hysteresis in Sm 0.05 Mn 0.95 S is observed in the magnetic fields 6 T < H < 9 T at low temperatures and linear magnetization dependence on field for compound with1 Introduction At present, much attention is focused on materials with strong correlation between magnetic and electrical properties [1][2][3]. In view of the practical applications, these compounds are promising for the creation of microelectronic elements; as far as the fundamental studies are concerned, the most intriguing are the materials containing variable-valence elements undergoing metalinsulator transitions and magnetic phase transformations including variations in magnetic properties at preservation of magnetic symmetry. Semiconductors EuS, SmS, and MnS [4][5][6][7] relate to these compounds. Rare-earth elements Eu and Sm have no electrons on 5d-orbitals and their electron configuration (without taking into account the 4f-orbitals) is similar to alkali-earth metals. The presence of 4f-and 5d-orbitals with relatively close energies causes a number of specific properties of the compounds containing these elements. A divalent samarium ion Sm 2þ possesses the same isoelectronic configuration as that of Eu 3þ and the transition energy E fd ¼ 0.4 eV from the 4f 6 -4f 5 ( 6 H)5d t 2g state [8]. The width of the gap (E g ) between the valence and conductivity bands in SmS is somewhat smaller compared to MnS. Under the external pressure P $ 6.5 kbar, the SmS lattice is abruptly compressed and the lattice parameter reaches the value a p ¼ 0.569 nm; resistivity decreases by an

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Concentration model of semiconductor-metal phase transitions in SmS

Cited by 5 publications

References 2 publications

Magnetic polaron bound to the positive muon in SmS: Exchange-driven formation of a mixed-valence state

Magnetic polaron bound to the positive muon in SmS: Exchange-driven formation of a mixed-valence state

Thermodynamics of the Point Defects in the Metallic Phase of the Samarium Monosulphide

Magnetic properties of Sm_xMn_1−xS solid solutions

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Concentration model of semiconductor-metal phase transitions in SmS

Cited by 5 publications

References 2 publications

Magnetic polaron bound to the positive muon in SmS: Exchange-driven formation of a mixed-valence state

Magnetic polaron bound to the positive muon in SmS: Exchange-driven formation of a mixed-valence state

Thermodynamics of the Point Defects in the Metallic Phase of the Samarium Monosulphide

Magnetic properties of SmxMn1−xS solid solutions

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Magnetic properties of Sm_xMn_1−xS solid solutions