The Experts below are selected from a list of 126 Experts worldwide ranked by ideXlab platform

Yoshihiko Okamoto - One of the best experts on this subject based on the ideXlab platform.

  • orbital transitions and frustrated magnetism in the kagome type Copper Mineral volborthite
    Inorganic Chemistry, 2019
    Co-Authors: Zenji Hiroi, Hajime Ishikawa, Hiroyuki Yoshida, Junichi Yamaura, Yoshihiko Okamoto
    Abstract:

    Volborthite Cu3V2O7(OH)2·2H2O is a Copper Mineral that materializes a two-dimensional quantum magnet comprising a kagome net of spin-1/2 Cu2+ ions. We prepared single crystals of volborthite using hydrothermal conditions and investigated their crystal structures and magnetic properties. Unusual orbital "switching" and "flipping" transitions were observed: in the former type of transition (switching), the Cu 3d orbital occupied by an unpaired electron changes between the d(3z2-r2) and d(x2-y2) types, and in the latter type of transition (flipping), the d(x2-y2)-type orbitals change their directions. Their origin is ascribed to variations in the orientation of water molecules in the gap between the kagome layers and the accompanying changes of hydrogen bonding. These orbital transitions dramatically modify the magnetic interactions between Cu2+ spins, from the anisotropic kagome type to the formation of spin trimers over the kagome net. The effective spin 1/2 generated on the trimers exhibits a frustrated magnetism, resulting in a rich phase diagram in the magnetic fields. Volborthite is a unique compound showing an exceptional interplay between the orbital and spin degrees of freedom.

  • distorted kagome lattice generated by a unique orbital arrangement in the Copper Mineral kcu3as2o7 oh 3
    Journal of the Physical Society of Japan, 2012
    Co-Authors: Yoshihiko Okamoto, Hajime Ishikawa, Goran J Nilsen, Zenji Hiroi
    Abstract:

    We study polycrystalline samples of KCu 3 As 2 O 7 (OH) 3 , a new candidate spin-1/2 kagome antiferromagnet, by magnetic susceptibility and heat capacity measurements above 2 K. The unique arrangement of the 3 z 2 - r 2 and x 2 - y 2 orbitals on the Cu 2+ kagome net is noted and compared to the orbital patterns found in other kagome Minerals. It is suggested that this orbital arrangement gives rise to one antiferromagnetic and two ferromagnetic interactions on isosceles triangles forming a highly distorted kagome lattice. KCu 3 As 2 O 7 (OH) 3 is found to show an antiferromagnetic long-range order at T N =7.2 K. Remarkably, a spin entropy is more gradually released upon cooling below T N compared with a conventional magnetic long-range order, which may originate from the geometrical frustration still present in this highly distorted kagome lattice.

Zenji Hiroi - One of the best experts on this subject based on the ideXlab platform.

  • orbital transitions and frustrated magnetism in the kagome type Copper Mineral volborthite
    Inorganic Chemistry, 2019
    Co-Authors: Zenji Hiroi, Hajime Ishikawa, Hiroyuki Yoshida, Junichi Yamaura, Yoshihiko Okamoto
    Abstract:

    Volborthite Cu3V2O7(OH)2·2H2O is a Copper Mineral that materializes a two-dimensional quantum magnet comprising a kagome net of spin-1/2 Cu2+ ions. We prepared single crystals of volborthite using hydrothermal conditions and investigated their crystal structures and magnetic properties. Unusual orbital "switching" and "flipping" transitions were observed: in the former type of transition (switching), the Cu 3d orbital occupied by an unpaired electron changes between the d(3z2-r2) and d(x2-y2) types, and in the latter type of transition (flipping), the d(x2-y2)-type orbitals change their directions. Their origin is ascribed to variations in the orientation of water molecules in the gap between the kagome layers and the accompanying changes of hydrogen bonding. These orbital transitions dramatically modify the magnetic interactions between Cu2+ spins, from the anisotropic kagome type to the formation of spin trimers over the kagome net. The effective spin 1/2 generated on the trimers exhibits a frustrated magnetism, resulting in a rich phase diagram in the magnetic fields. Volborthite is a unique compound showing an exceptional interplay between the orbital and spin degrees of freedom.

  • Possible observation of quantum spin-nematic phase in a frustrated magnet
    'Proceedings of the National Academy of Sciences', 2019
    Co-Authors: Yoshimitsu Kohama, Hajime Ishikawa, Akira Matsuo, Koichi Kindo, Nic Shannon, Zenji Hiroi
    Abstract:

    Water freezes into ice in winter and evaporates into vapor in summer. Scientifically, the transformations between solid, liquid, and gas are called phase transitions and can be classified through the changes in symmetry which occur in each case. A fourth phase of matter was discovered late in the 19th century: the liquid crystal nematic, in which rod- or disk-shaped molecules align like the atoms in a solid, while continuing to flow like a liquid. Here we report thermodynamic evidence of a quantum analog of the classical nematic phase, the quantum spin nematic (SN). In an SN, the spins of a quantum magnet select a common axis, like a nematic liquid crystal, while escaping conventional magnetic order. Our state-ofthe-art thermal measurements in high pulsed magnetic fields up to 33 T on the Copper Mineral volborthite with spin 1/2 on a frustrated lattice provide thermodynamic evidence for SN order, half a century after the theoretical proposal [Blume M, Hsieh YY (1969) J Appl Phys 40:1249; Andreev AF, Grishchuk IA (1984) J Exp Theor Phys 97:467-475]

  • distorted kagome lattice generated by a unique orbital arrangement in the Copper Mineral kcu3as2o7 oh 3
    Journal of the Physical Society of Japan, 2012
    Co-Authors: Yoshihiko Okamoto, Hajime Ishikawa, Goran J Nilsen, Zenji Hiroi
    Abstract:

    We study polycrystalline samples of KCu 3 As 2 O 7 (OH) 3 , a new candidate spin-1/2 kagome antiferromagnet, by magnetic susceptibility and heat capacity measurements above 2 K. The unique arrangement of the 3 z 2 - r 2 and x 2 - y 2 orbitals on the Cu 2+ kagome net is noted and compared to the orbital patterns found in other kagome Minerals. It is suggested that this orbital arrangement gives rise to one antiferromagnetic and two ferromagnetic interactions on isosceles triangles forming a highly distorted kagome lattice. KCu 3 As 2 O 7 (OH) 3 is found to show an antiferromagnetic long-range order at T N =7.2 K. Remarkably, a spin entropy is more gradually released upon cooling below T N compared with a conventional magnetic long-range order, which may originate from the geometrical frustration still present in this highly distorted kagome lattice.

Mario Vera - One of the best experts on this subject based on the ideXlab platform.

  • Data_Sheet_2_Weak Iron Oxidation by Sulfobacillus thermosulfidooxidans Maintains a Favorable Redox Potential for Chalcopyrite Bioleaching.xls
    2018
    Co-Authors: Stephan Christel, Malte Herold, Sören Bellenberg, Antoine Buetti-dinh, Mohamed El Hajjami, Igor V. Pivkin, Wolfgang Sand, Paul Wilmes, Ansgar Poetsch, Mario Vera
    Abstract:

    Bioleaching is an emerging technology, describing the microbially assisted dissolution of sulfidic ores that provides a more environmentally friendly alternative to many traditional metal extraction methods, such as roasting or smelting. Industrial interest is steadily increasing and today, circa 15–20% of the world’s Copper production can be traced back to this method. However, bioleaching of the world’s most abundant Copper Mineral chalcopyrite suffers from low dissolution rates, often attributed to passivating layers, which need to be overcome to use this technology to its full potential. To prevent these passivating layers from forming, leaching needs to occur at a low oxidation/reduction potential (ORP), but chemical redox control in bioleaching heaps is difficult and costly. As an alternative, selected weak iron-oxidizers could be employed that are incapable of scavenging exceedingly low concentrations of iron and therefore, raise the ORP just above the onset of bioleaching, but not high enough to allow for the occurrence of passivation. In this study, we report that microbial iron oxidation by Sulfobacillus thermosulfidooxidans meets these specifications. Chalcopyrite concentrate bioleaching experiments with S. thermosulfidooxidans as the sole iron oxidizer exhibited significantly lower redox potentials and higher release of Copper compared to communities containing the strong iron oxidizer Leptospirillum ferriphilum. Transcriptomic response to single and co-culture of these two iron oxidizers was studied and revealed a greatly decreased number of mRNA transcripts ascribed to iron oxidation in S. thermosulfidooxidans when cultured in the presence of L. ferriphilum. This allowed for the identification of genes potentially responsible for S. thermosulfidooxidans’ weaker iron oxidation to be studied in the future, as well as underlined the need for new mechanisms to control the microbial population in bioleaching heaps.

  • Data_Sheet_1_Weak Iron Oxidation by Sulfobacillus thermosulfidooxidans Maintains a Favorable Redox Potential for Chalcopyrite Bioleaching.PDF
    2018
    Co-Authors: Stephan Christel, Malte Herold, Sören Bellenberg, Antoine Buetti-dinh, Mohamed El Hajjami, Igor V. Pivkin, Wolfgang Sand, Paul Wilmes, Ansgar Poetsch, Mario Vera
    Abstract:

    Bioleaching is an emerging technology, describing the microbially assisted dissolution of sulfidic ores that provides a more environmentally friendly alternative to many traditional metal extraction methods, such as roasting or smelting. Industrial interest is steadily increasing and today, circa 15–20% of the world’s Copper production can be traced back to this method. However, bioleaching of the world’s most abundant Copper Mineral chalcopyrite suffers from low dissolution rates, often attributed to passivating layers, which need to be overcome to use this technology to its full potential. To prevent these passivating layers from forming, leaching needs to occur at a low oxidation/reduction potential (ORP), but chemical redox control in bioleaching heaps is difficult and costly. As an alternative, selected weak iron-oxidizers could be employed that are incapable of scavenging exceedingly low concentrations of iron and therefore, raise the ORP just above the onset of bioleaching, but not high enough to allow for the occurrence of passivation. In this study, we report that microbial iron oxidation by Sulfobacillus thermosulfidooxidans meets these specifications. Chalcopyrite concentrate bioleaching experiments with S. thermosulfidooxidans as the sole iron oxidizer exhibited significantly lower redox potentials and higher release of Copper compared to communities containing the strong iron oxidizer Leptospirillum ferriphilum. Transcriptomic response to single and co-culture of these two iron oxidizers was studied and revealed a greatly decreased number of mRNA transcripts ascribed to iron oxidation in S. thermosulfidooxidans when cultured in the presence of L. ferriphilum. This allowed for the identification of genes potentially responsible for S. thermosulfidooxidans’ weaker iron oxidation to be studied in the future, as well as underlined the need for new mechanisms to control the microbial population in bioleaching heaps.

Dopson Mark - One of the best experts on this subject based on the ideXlab platform.

  • Weak Iron Oxidation by Sulfobacillus thermosulfidooxidans Maintains a Favorable Redox Potential for Chalcopyrite Bioleaching
    'Frontiers Media SA', 2018
    Co-Authors: Christel Stephan, Bellenberg Soren, El Hajjami Mohamed, Buetti-dinh Antoine, Pivkin Igor, Sand Wolfgang, Wilmes Paul, Poetsch Ansgar, Herold Malte, Dopson Mark
    Abstract:

    Bioleaching is an emerging technology, describing the microbially assisted dissolution of sulfidic ores that provides a more environmentally friendly alternative to many traditional metal extraction methods, such as roasting or smelting. Industrial interest is steadily increasing and today, circa 15–20% of the world’s Copper production can be traced back to this method. However, bioleaching of the world’s most abundant Copper Mineral chalcopyrite suffers from low dissolution rates, often attributed to passivating layers, which need to be overcome to use this technology to its full potential. To prevent these passivating layers from forming, leaching needs to occur at a low oxidation/reduction potential (ORP), but chemical redox control in bioleaching heaps is difficult and costly. As an alternative, selected weak iron-oxidizers could be employed that are incapable of scavenging exceedingly low concentrations of iron and therefore, raise the ORP just above the onset of bioleaching, but not high enough to allow for the occurrence of passivation. In this study, we report that microbial iron oxidation by Sulfobacillus thermosulfidooxidans meets these specifications. Chalcopyrite concentrate bioleaching experiments with S. thermosulfidooxidans as the sole iron oxidizer exhibited significantly lower redox potentials and higher release of Copper compared to communities containing the strong iron oxidizer Leptospirillum ferriphilum. Transcriptomic response to single and co-culture of these two iron oxidizers was studied and revealed a greatly decreased number of mRNA transcripts ascribed to iron oxidation in S. thermosulfidooxidans when cultured in the presence of L. ferriphilum. This allowed for the identification of genes potentially responsible for S. thermosulfidooxidans’ weaker iron oxidation to be studied in the future, as well as underlined the need for new mechanisms to control the microbial population in bioleaching heaps

  • Multi-omics reveal the lifestyle of the acidophilic, Mineral-oxidizing model species Leptospirillum ferriphilum(T).
    2017
    Co-Authors: Christel Stephan(*), Herold Malte(*), Bellenberg Soren, El Hajjami Mohamed, Buetti-dinh Antoine, Pivkin Igor, Sand Wolfgang, Wilmes Paul, Poetsch Ansgar, Dopson Mark
    Abstract:

    Leptospirillum ferriphilum plays a major role in acidic, metal rich environments where it represents one of the most prevalent iron oxidizers. These milieus include acid rock and mine drainage as well as biomining operations. Despite its perceived importance, no complete genome sequence of this model species' type strain is available, limiting the possibilities to investigate the strategies and adaptations Leptospirillum ferriphilum(T) applies to survive and compete in its niche. This study presents a complete, circular genome of Leptospirillum ferriphilum(T) DSM 14647 obtained by PacBio SMRT long read sequencing for use as a high quality reference. Analysis of the functionally annotated genome, mRNA transcripts, and protein concentrations revealed a previously undiscovered nitrogenase cluster for atmospheric nitrogen fixation and elucidated metabolic systems taking part in energy conservation, carbon fixation, pH homeostasis, heavy metal tolerance, oxidative stress response, chemotaxis and motility, quorum sensing, and biofilm formation. Additionally, mRNA transcript counts and protein concentrations were compared between cells grown in continuous culture using ferrous iron as substrate and bioleaching cultures containing chalcopyrite (CuFeS2). Leptospirillum ferriphilum(T) adaptations to growth on chalcopyrite included a possibly enhanced production of reducing power, reduced carbon dioxide fixation, as well as elevated RNA transcripts and proteins involved in heavy metal resistance, with special emphasis on Copper efflux systems. Finally, expression and translation of genes responsible for chemotaxis and motility were enhanced.IMPORTANCELeptospirillum ferriphilum is one of the most important iron-oxidizers in the context of acidic and metal rich environments during moderately thermophilic biomining. A high-quality circular genome of Leptospirillum ferriphilum(T) coupled with functional omics data provides new insights into its metabolic properties, such as the novel identification of genes for atmospheric nitrogen fixation, and represents an essential step for further accurate proteomic and transcriptomic investigation of this acidophile model species in the future. Additionally, light is shed on Leptospirillum ferriphilum(T) adaptation strategies to growth on the Copper Mineral chalcopyrite. This data can be applied to deepen our understanding and optimization of bioleaching and biooxidation, techniques that present sustainable and environmentally friendly alternatives to many traditional methods for metal extraction

Hajime Ishikawa - One of the best experts on this subject based on the ideXlab platform.

  • orbital transitions and frustrated magnetism in the kagome type Copper Mineral volborthite
    Inorganic Chemistry, 2019
    Co-Authors: Zenji Hiroi, Hajime Ishikawa, Hiroyuki Yoshida, Junichi Yamaura, Yoshihiko Okamoto
    Abstract:

    Volborthite Cu3V2O7(OH)2·2H2O is a Copper Mineral that materializes a two-dimensional quantum magnet comprising a kagome net of spin-1/2 Cu2+ ions. We prepared single crystals of volborthite using hydrothermal conditions and investigated their crystal structures and magnetic properties. Unusual orbital "switching" and "flipping" transitions were observed: in the former type of transition (switching), the Cu 3d orbital occupied by an unpaired electron changes between the d(3z2-r2) and d(x2-y2) types, and in the latter type of transition (flipping), the d(x2-y2)-type orbitals change their directions. Their origin is ascribed to variations in the orientation of water molecules in the gap between the kagome layers and the accompanying changes of hydrogen bonding. These orbital transitions dramatically modify the magnetic interactions between Cu2+ spins, from the anisotropic kagome type to the formation of spin trimers over the kagome net. The effective spin 1/2 generated on the trimers exhibits a frustrated magnetism, resulting in a rich phase diagram in the magnetic fields. Volborthite is a unique compound showing an exceptional interplay between the orbital and spin degrees of freedom.

  • Possible observation of quantum spin-nematic phase in a frustrated magnet
    'Proceedings of the National Academy of Sciences', 2019
    Co-Authors: Yoshimitsu Kohama, Hajime Ishikawa, Akira Matsuo, Koichi Kindo, Nic Shannon, Zenji Hiroi
    Abstract:

    Water freezes into ice in winter and evaporates into vapor in summer. Scientifically, the transformations between solid, liquid, and gas are called phase transitions and can be classified through the changes in symmetry which occur in each case. A fourth phase of matter was discovered late in the 19th century: the liquid crystal nematic, in which rod- or disk-shaped molecules align like the atoms in a solid, while continuing to flow like a liquid. Here we report thermodynamic evidence of a quantum analog of the classical nematic phase, the quantum spin nematic (SN). In an SN, the spins of a quantum magnet select a common axis, like a nematic liquid crystal, while escaping conventional magnetic order. Our state-ofthe-art thermal measurements in high pulsed magnetic fields up to 33 T on the Copper Mineral volborthite with spin 1/2 on a frustrated lattice provide thermodynamic evidence for SN order, half a century after the theoretical proposal [Blume M, Hsieh YY (1969) J Appl Phys 40:1249; Andreev AF, Grishchuk IA (1984) J Exp Theor Phys 97:467-475]

  • distorted kagome lattice generated by a unique orbital arrangement in the Copper Mineral kcu3as2o7 oh 3
    Journal of the Physical Society of Japan, 2012
    Co-Authors: Yoshihiko Okamoto, Hajime Ishikawa, Goran J Nilsen, Zenji Hiroi
    Abstract:

    We study polycrystalline samples of KCu 3 As 2 O 7 (OH) 3 , a new candidate spin-1/2 kagome antiferromagnet, by magnetic susceptibility and heat capacity measurements above 2 K. The unique arrangement of the 3 z 2 - r 2 and x 2 - y 2 orbitals on the Cu 2+ kagome net is noted and compared to the orbital patterns found in other kagome Minerals. It is suggested that this orbital arrangement gives rise to one antiferromagnetic and two ferromagnetic interactions on isosceles triangles forming a highly distorted kagome lattice. KCu 3 As 2 O 7 (OH) 3 is found to show an antiferromagnetic long-range order at T N =7.2 K. Remarkably, a spin entropy is more gradually released upon cooling below T N compared with a conventional magnetic long-range order, which may originate from the geometrical frustration still present in this highly distorted kagome lattice.