Electronic Variations in Carbonate- and Phosphane-Related 24- and 26-Electron E4 Clusters of Silicon and Germanium

Nesper, Reinard; Wengert, Steffen; Zürcher, F.; Currao, Antonio

doi:10.1002/(sici)1521-3765(19991105)5:11<3382::aid-chem3382>3.3.co;2-t

Cited by 15 publications

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“…Investigations of the band structure by means of density functional calculations carried out on the theoretical model Eu 8 Mg 15 Si 13 reveal, consistent with the band structure of the isostructural Ba 5 Mg 18 Si 13 , [7] a density of states (DOS) at the Fermi level ( Figure 3). This arises mainly from the p states of the [Si 4 ] unit.…”

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“…Tetrel compounds such as M 5+x Mg 18Àx T 13 (M = Sr, Ba; Tt = Si, Ge), which crystallize in their own structure type, have been known for some time. [7] The structure usually contains isolated Si 4À anions as well as planar Si 4 clusters for which different valence electron numbers have been found. [7,8] Moreover, the tetrel center of the Tt 4 cluster can be replaced by a metal such as Li or Mg without causing a structural change in the geometrical pattern.…”

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“…[7] The structure usually contains isolated Si 4À anions as well as planar Si 4 clusters for which different valence electron numbers have been found. [7,8] Moreover, the tetrel center of the Tt 4 cluster can be replaced by a metal such as Li or Mg without causing a structural change in the geometrical pattern. Recently, we reported on the synthesis of the phase Eu 5+x Mg 18Àx Ge 13 (x = 0.1), which is isostructural with Sr 6.3 Mg 16.7 Si 13 and isopunctual with Eu 8 Mg 16 Ge 12 .…”

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“…The bond lengths of 2.56 between the terminal and central atom are within the range of elongated single bonds. Similar to many tetrel Zintl phases the anions are ecliptically stacked [7] so that their partially depopulated p* orbitals interact in the [001] direction over a distance of approximately 4.4 . The trigonal-prismatic coordination of the central silicon atom by europium neighbors follows the wellknown pattern of Zintl phases containing divalent rare-earth and alkaline-earth metals.…”

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“…This may also be the case for the title compound, because the lability of the [E 4 ] 10À anion (E = Si, Ge) can lead to metallic or semiconducting behavior. [7,9] We have synthesized the new compound Eu 5+x Mg 18Àx Si 13 (x = 2.2) and observed an unusual magnetoresistive behavior. Contrary to already known MR materials, the magnetoresistivity exhibits a maximum at low temperatures.…”

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Field‐Induced Inversion of the Magnetoresistive Effect in the Zintl Phase Eu_5+xMg_18−xSi₁₃ (x=2.2)

et al. 2013

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The discovery of giant magnetoresistance (GMR effect) [1] in magnetic multilayers has led to a rapid technological advance in spintronic research and device building, for example, magnetoresistive random-access memory (MRAM). The operating principle is based on the dependence of the electrical resistivity on the spin alignment in the magnetic domains of the material. [2] All ferromagnetic metals exhibit a finite but small change of the electronic conductivity after application of an external magnetic field. The value of the magnetoresistivity MR under applied magnetic field H is defined as MR = [1(H)À1(0)]/1(0)] 100 % (1 = electrical resistivity) and can be either positive or negative. If the resistance drop is associated with critical ferromagnetic fluctuations, this phenomenon is called colossal magnetoresistance (CMR). This effect was observed for the first time for the manganese perovskites RE 1Àx B x MnO 3 (RE = rareearth metal; B = divalent cation). [3] The discovery of enhanced MR, often described as CMR in the literature, for the ternary Zintl phase [4] Eu 14 MnSb 11 has led to intensive investigations of this class of compounds. [5] The MR effect occurs simultaneously with ferromagnetic ordering due to the parallel alignment of the unpaired 4f electrons of the rare-earth metals. In the case of Eu 2+ ions they should contribute with a local magnetic moment of 7.94 m B.We report herein on the synthesis of the new ternary Zintl phase Eu 5+x Mg 18Àx Si 13 (x = 2.2) [6] which displays an unusual MR effect. The title compound does not show a maximum of the resistivity at low temperatures and no saturation at fields up to 6 T. Furthermore, an inversion of the sign of the MR as a function of applied field and temperature can be observed.The crystal structure of Eu 5+x Mg 18Àx Si 13 (x = 2.2) is depicted in Figure 1. Tetrel compounds such as M 5+x Mg 18Àx T 13 (M = Sr, Ba; Tt = Si, Ge), which crystallize in their own structure type, have been known for some time. [7] The structure usually contains isolated Si 4À anions as well as planar Si 4 clusters for which different valence electron numbers have been found. [7,8] Moreover, the tetrel center of the Tt 4 cluster can be replaced by a metal such as Li or Mg without causing a structural change in the geometrical pattern. Recently, we reported on the synthesis of the phase Eu 5+x Mg 18Àx Ge 13 (x = 0.1), which is isostructural with Sr 6.3 Mg 16.7 Si 13 and isopunctual with Eu 8 Mg 16 Ge 12 . In the new compound the Tt 4 unit collapses into three isolated Tt 4À anions by means of such substitution. [9] This indicates the remarkable flexibility of that structure type, which we have tested now by systematic changes of the composition and investigated the related electronic effects.The electronic structure of the title compound can be interpreted according to the Zintl-Klemm concept as (Eu 2+ ) 5+x (Mg 2+ ) 18Àx (Si 4À ) 9 (Si 4 10À ) with nine isolated silicon anions and a planar [Si 4 ] unit. [6,9] The anisotropic displacement ellipsoid of the central silicon atom...

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confidence: 72%

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confidence: 99%

mentioning

confidence: 99%

mentioning

confidence: 99%

mentioning

confidence: 99%

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Field‐Induced Inversion of the Magnetoresistive Effect in the Zintl Phase Eu_5+xMg_18−xSi₁₃ (x=2.2)

et al. 2013

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Feldinduzierte Inversion des magnetoresistiven Effekts in der Zintl‐Phase Eu_5+xMg_18−xSi₁₃ (x=2.2)

et al. 2013

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Die Entdeckung des Riesenmagnetowiderstands (GMR-Effekt) [1] in magnetischen Mehrfachschichten hat zu einem rasanten technologischen Fortschritt bei metallischen spintronischen Bauelementen geführt, wie z. B. dem magnetoresistiven Direktzugriffspeicher (MRAM). Das Operationsprinzip basiert auf der Abhängigkeit des elektrischen Widerstands von der Anordnung der Spins in magnetischen Domänen des Materials. [2] Alle ferromagnetischen Metalle zeigen eine endliche, jedoch kleine ¾nderung des elektrischen Widerstands nach Anlegen eines Magnetfeldes. Der Magnetowiderstandswert bei einem bestimmten Magnetfeld H ist definiert als MR = [1(H)À1(0)]/1(0)] 100 % (1 = elektrischer Widerstand) und kann sowohl negative wie auch positive Werte annehmen. Steht der Widerstandsabfall in Zusammenhang mit kritischen ferromagnetischen Fluktuationen, wird dieses Phänomen als kolossaler Magnetowiderstand (CMR) bezeichnet. Dieser Effekt wurde zuerst für Manganperowskite SE 1Àx B x MnO 3 (SE = Seltenerdmetall; B = divalentes Kation) beobachtet. [3] Die Entdeckung des erhçhten MR-Effekts, in der Literatur oft auch als CMR-Effekt bezeichnet, für die ternäre Zintl-Phase [4] Eu 14 MnSb 11 hat zu verstärkten Untersuchungen dieser Verbindungsklasse geführt. [5] Bisher sind für Zintl-Phasen hohe MR-Werte nur bei niedrigen Temperaturen bekannt, und es wurde noch nicht über Vorzeichenänderung der Magnetoresistivität berichtet. Der MR-Effekt hängt mit der ferromagnetischen Ordnung der ungepaarten 4f-Elektronen der Seltenerdmetalle zusammen. Im Falle von Eu 2+ -Ionen wird ein hohes magnetisches Moment von 7.94 m B induziert. Hier berichten wir über die Synthese der neuen ternären Zintl-Phase Eu 5+x Mg 18Àx Si 13 (x = 2.2), [6] die einen ungewçhnlichen MR-Effekt zeigt. Man findet hier kein Maximum bei tiefen Temperaturen und keine Sättigung bis 6 T. Darüber hinaus tritt ein Vorzeichenwechsel des MR-Effekts als Funktion des Magnetfeldes und der Temperatur auf. Die Kristallstruktur von Eu 5+x Mg 18Àx Si 13 ist in der Abbildung 1 dargestellt. Tetrelverbindungen der Art M 5+x Mg 18Àx Tt 13 (M = Sr, Ba; Tt = Si, Ge), die in einem eigenen Strukturtyp kristallisieren, sind bereits seit einiger Zeit bekannt. [7] Die Struktur enthält in der Regel neben isolierten Si 4À -Zintl-Anionen planare Si 4 -Cluster, für die unterschiedliche Valenzelektronenzahlen gefunden wurden. [7, 8] Zudem kann das Tetrel-Zentrum des Tt 4 -Clusters durch ein Metall wie z. B. Li, Mg etc. ersetzt werden, ohne dass sich das geometrische Muster der Struktur verändert. Vor kurzem berichteten wir über die Synthese der Phase Eu 5+x Mg 18Àx Ge 13 (x = 0.1), die isostrukturell mit Sr 6.3 Mg 16.7 Si 13 und isopunktuell mit der Verbindung Eu 8 Mg 16 Ge 12 ist, bei der durch einen solchen Ersatz die Tt 4 -Einheit zu drei isolierten Tt 4À -Anionen zerfällt. [9] Dies deutet auf die beachtliche Flexibilität des Strukturtyps hin, die wir nun durch systematische Veränderungen der Zusammensetzung getestet und dabei spezielle elektronische Effekte untersucht haben. Die Verbindung kann nach dem Zintl-Kl...

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Transition‐Metal‐Rich Borides – Fascinating Crystal Structures and Magnetic Properties

Fokwa

2010

Eur J Inorg Chem

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The ability to design and predict new phases in solid-state chemistry remains a challenge. However, experiment and theory have been working together in the last decade to find new phases with targeted magnetic properties in the family of transition-metal-rich borides. These studies were very successful for boride phases crystallizing with the Ti 3 Co 5 B 2 structure type. Furthermore, strong variations of the magnetic properties in some series of compounds as a function of the number of valence electrons were observed experimentally and explained by using density functional theory calcu-

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Electronic Variations in Carbonate- and Phosphane-Related 24- and 26-Electron E4 Clusters of Silicon and Germanium

Cited by 15 publications

References 0 publications

Field‐Induced Inversion of the Magnetoresistive Effect in the Zintl Phase Eu_5+xMg_18−xSi₁₃ (x=2.2)

Field‐Induced Inversion of the Magnetoresistive Effect in the Zintl Phase Eu_5+xMg_18−xSi₁₃ (x=2.2)

Feldinduzierte Inversion des magnetoresistiven Effekts in der Zintl‐Phase Eu_5+xMg_18−xSi₁₃ (x=2.2)

Transition‐Metal‐Rich Borides – Fascinating Crystal Structures and Magnetic Properties

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Electronic Variations in Carbonate- and Phosphane-Related 24- and 26-Electron E4 Clusters of Silicon and Germanium

Cited by 15 publications

References 0 publications

Field‐Induced Inversion of the Magnetoresistive Effect in the Zintl Phase Eu5+xMg18−xSi13 (x=2.2)

Field‐Induced Inversion of the Magnetoresistive Effect in the Zintl Phase Eu5+xMg18−xSi13 (x=2.2)

Feldinduzierte Inversion des magnetoresistiven Effekts in der Zintl‐Phase Eu5+xMg18−xSi13 (x=2.2)

Transition‐Metal‐Rich Borides – Fascinating Crystal Structures and Magnetic Properties

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Field‐Induced Inversion of the Magnetoresistive Effect in the Zintl Phase Eu_5+xMg_18−xSi₁₃ (x=2.2)

Field‐Induced Inversion of the Magnetoresistive Effect in the Zintl Phase Eu_5+xMg_18−xSi₁₃ (x=2.2)

Feldinduzierte Inversion des magnetoresistiven Effekts in der Zintl‐Phase Eu_5+xMg_18−xSi₁₃ (x=2.2)