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Christian Näther - One of the best experts on this subject based on the ideXlab platform.
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preparation of new ligand deficient thiocyanato compounds with cooperative Magnetic Phenomena by thermal decomposition of their ligand rich precursors
European Journal of Inorganic Chemistry, 2010Co-Authors: Mario Wriedt, Christian NätherAbstract:The reaction of nickel thiocyanate with bipy (4,4'-bipyridine) in water at room temperature leads to the formation of the ligand-rich 1:2 (1:2 ratio between metal salt and organic ligand) hydrate [[Ni(NCS) 2 (bipy)(H 2 O) 2 }•(bipy)] n (1-Ni), which is isotypic to its analogues 1-Mn and 1-Co reported recently. In their crystal structure, the metal cations are coordinated by two terminal N-bonded thiocyanato anions, two water molecules, and two bridging bipy ligands in an octahedral coordination mode. These building blocks elongate in linear M-bipy-M chains, which are further connected by hydrogen bonds between H 2 O and noncoordinated bipy ligands into layers. On heating these precursor compounds, two-step decomposition is observed: New ligand-rich 1:2 anhydrous compounds [M(NCS) 2 (bipy) 2 ] n [M = Mn (2-Mn), Co (2-Co), and Ni (2-Ni)] could be identified as intermediates in the first heating step, and new ligand-deficient 1:1 compounds [M(NCS) 2 (bipy)] n [M = Mn (3-Mn), Co (3-Co), and Ni (3-Ni)] could be identified as intermediates in the second heating step. A smooth reaction pathway in their crystal structures is observed: First, water is removed, leading to directly coordinating bipy ligands, and second, half of the bipy ligands are removed, leading to μ-1,3-bridging thiocyanato anions. This structural transformation is accompanied by a dramatic change in their Magnetic properties: Whereas the ligand-rich 1:2 hydrates and anhydrous compounds show only Curie-Weiss paramagnetism, the ligand-deficient 1:1 intermediates show either Curie-Weiss paramagnetism or antiferroMagnetic ordering at lower temperatures, mediated by the bridging thiocyanato anions. These results are qualitatively compared with those of the related ligand-rich and ligand-deficient compounds with pyrazine and pyrimidine.
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thermal decomposition reactions as tool for the synthesis of new metal thiocyanate diazine coordination polymers with cooperative Magnetic Phenomena
Inorganic Chemistry, 2009Co-Authors: Mario Wriedt, Sina Sellmer, Christian NätherAbstract:Reaction of nickel thiocyanate with pyrimidine at room temperature leads to the formation of the new ligand-rich 1:2 (1:2 = ratio between metal and ligand) compound [Ni(NCS)2(pyrimidine)2]n (2) which is isotypic to [Co(NCS)2(pyrimidine)2]n (1) reported recently. In the crystal structure, the Ni2+ ions are coordinated by four N atoms of pyrimidine ligands, which connect the metal centers into layers, and two N atoms of terminal bonded thiocyanato anions within slightly distorted octahedra. If the synthesis is performed under solvothermal conditions and an excess of the metal thiocyanate is used, single crystals of the ligand-deficient 1:1 compound [Ni(NCS)2(pyrimidine)]n (4) are obtained. Investigations on the synthesis of this compound show that it is always contaminated with large amounts of the corresponding ligand-rich 1:2 compound 2. In the crystal structure, the Ni2+ ions are coordinated by two N atoms of pyrimidine ligands, which connect the metal centers into chains, and two N atoms as well as two ...
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thermal decomposition reactions as tool for the synthesis of new metal thiocyanate diazine coordination polymers with cooperative Magnetic Phenomena
Inorganic Chemistry, 2009Co-Authors: Mario Wriedt, Sina Sellmer, Christian NätherAbstract:Reaction of nickel thiocyanate with pyrimidine at room temperature leads to the formation of the new ligand-rich 1:2 (1:2 = ratio between metal and ligand) compound [Ni(NCS)(2)(pyrimidine)(2)](n) (2) which is isotypic to [Co(NCS)(2)(pyrimidine)(2)](n) (1) reported recently. In the crystal structure, the Ni(2+) ions are coordinated by four N atoms of pyrimidine ligands, which connect the metal centers into layers, and two N atoms of terminal bonded thiocyanato anions within slightly distorted octahedra. If the synthesis is performed under solvothermal conditions and an excess of the metal thiocyanate is used, single crystals of the ligand-deficient 1:1 compound [Ni(NCS)(2)(pyrimidine)](n) (4) are obtained. Investigations on the synthesis of this compound show that it is always contaminated with large amounts of the corresponding ligand-rich 1:2 compound 2. In the crystal structure, the Ni(2+) ions are coordinated by two N atoms of pyrimidine ligands, which connect the metal centers into chains, and two N atoms as well as two S atoms of mu-1,3 bridged thiocyanato anions, which conntect these chains into layers, within a slightly distorted octahedral geometry. On heating compounds 1 and 2 transform quantitatively into the ligand-deficient 1:1 Ni compound 4 and its isotypic Co compound 3. If nickel and cobalt thiocyanate are reacted with an excess of pyrimidine in a solvent-free reaction, discrete ligand-rich 1:4 complexes of composition [M(NCS)(2)(pyrimidine)(4)] (M = Co 5 and Ni 6) are obtained, which could be determined by single crystal structure analysis. In their crystal structure the metal ions are coordinated by four terminal bonded pyrimidine ligands and two terminal N-bonded thiocyanato anions. For the ligand-rich 1:2 and ligand-deficient 1:1 compounds Magnetic measurements were performed, which reveal different Magnetic properties: The 1:2 compounds show a ferroMagnetic and the 1:1 compounds an antiferroMagnetic ordering at lower temperatures.
Mario Wriedt - One of the best experts on this subject based on the ideXlab platform.
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preparation of new ligand deficient thiocyanato compounds with cooperative Magnetic Phenomena by thermal decomposition of their ligand rich precursors
European Journal of Inorganic Chemistry, 2010Co-Authors: Mario Wriedt, Christian NätherAbstract:The reaction of nickel thiocyanate with bipy (4,4'-bipyridine) in water at room temperature leads to the formation of the ligand-rich 1:2 (1:2 ratio between metal salt and organic ligand) hydrate [[Ni(NCS) 2 (bipy)(H 2 O) 2 }•(bipy)] n (1-Ni), which is isotypic to its analogues 1-Mn and 1-Co reported recently. In their crystal structure, the metal cations are coordinated by two terminal N-bonded thiocyanato anions, two water molecules, and two bridging bipy ligands in an octahedral coordination mode. These building blocks elongate in linear M-bipy-M chains, which are further connected by hydrogen bonds between H 2 O and noncoordinated bipy ligands into layers. On heating these precursor compounds, two-step decomposition is observed: New ligand-rich 1:2 anhydrous compounds [M(NCS) 2 (bipy) 2 ] n [M = Mn (2-Mn), Co (2-Co), and Ni (2-Ni)] could be identified as intermediates in the first heating step, and new ligand-deficient 1:1 compounds [M(NCS) 2 (bipy)] n [M = Mn (3-Mn), Co (3-Co), and Ni (3-Ni)] could be identified as intermediates in the second heating step. A smooth reaction pathway in their crystal structures is observed: First, water is removed, leading to directly coordinating bipy ligands, and second, half of the bipy ligands are removed, leading to μ-1,3-bridging thiocyanato anions. This structural transformation is accompanied by a dramatic change in their Magnetic properties: Whereas the ligand-rich 1:2 hydrates and anhydrous compounds show only Curie-Weiss paramagnetism, the ligand-deficient 1:1 intermediates show either Curie-Weiss paramagnetism or antiferroMagnetic ordering at lower temperatures, mediated by the bridging thiocyanato anions. These results are qualitatively compared with those of the related ligand-rich and ligand-deficient compounds with pyrazine and pyrimidine.
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thermal decomposition reactions as tool for the synthesis of new metal thiocyanate diazine coordination polymers with cooperative Magnetic Phenomena
Inorganic Chemistry, 2009Co-Authors: Mario Wriedt, Sina Sellmer, Christian NätherAbstract:Reaction of nickel thiocyanate with pyrimidine at room temperature leads to the formation of the new ligand-rich 1:2 (1:2 = ratio between metal and ligand) compound [Ni(NCS)2(pyrimidine)2]n (2) which is isotypic to [Co(NCS)2(pyrimidine)2]n (1) reported recently. In the crystal structure, the Ni2+ ions are coordinated by four N atoms of pyrimidine ligands, which connect the metal centers into layers, and two N atoms of terminal bonded thiocyanato anions within slightly distorted octahedra. If the synthesis is performed under solvothermal conditions and an excess of the metal thiocyanate is used, single crystals of the ligand-deficient 1:1 compound [Ni(NCS)2(pyrimidine)]n (4) are obtained. Investigations on the synthesis of this compound show that it is always contaminated with large amounts of the corresponding ligand-rich 1:2 compound 2. In the crystal structure, the Ni2+ ions are coordinated by two N atoms of pyrimidine ligands, which connect the metal centers into chains, and two N atoms as well as two ...
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thermal decomposition reactions as tool for the synthesis of new metal thiocyanate diazine coordination polymers with cooperative Magnetic Phenomena
Inorganic Chemistry, 2009Co-Authors: Mario Wriedt, Sina Sellmer, Christian NätherAbstract:Reaction of nickel thiocyanate with pyrimidine at room temperature leads to the formation of the new ligand-rich 1:2 (1:2 = ratio between metal and ligand) compound [Ni(NCS)(2)(pyrimidine)(2)](n) (2) which is isotypic to [Co(NCS)(2)(pyrimidine)(2)](n) (1) reported recently. In the crystal structure, the Ni(2+) ions are coordinated by four N atoms of pyrimidine ligands, which connect the metal centers into layers, and two N atoms of terminal bonded thiocyanato anions within slightly distorted octahedra. If the synthesis is performed under solvothermal conditions and an excess of the metal thiocyanate is used, single crystals of the ligand-deficient 1:1 compound [Ni(NCS)(2)(pyrimidine)](n) (4) are obtained. Investigations on the synthesis of this compound show that it is always contaminated with large amounts of the corresponding ligand-rich 1:2 compound 2. In the crystal structure, the Ni(2+) ions are coordinated by two N atoms of pyrimidine ligands, which connect the metal centers into chains, and two N atoms as well as two S atoms of mu-1,3 bridged thiocyanato anions, which conntect these chains into layers, within a slightly distorted octahedral geometry. On heating compounds 1 and 2 transform quantitatively into the ligand-deficient 1:1 Ni compound 4 and its isotypic Co compound 3. If nickel and cobalt thiocyanate are reacted with an excess of pyrimidine in a solvent-free reaction, discrete ligand-rich 1:4 complexes of composition [M(NCS)(2)(pyrimidine)(4)] (M = Co 5 and Ni 6) are obtained, which could be determined by single crystal structure analysis. In their crystal structure the metal ions are coordinated by four terminal bonded pyrimidine ligands and two terminal N-bonded thiocyanato anions. For the ligand-rich 1:2 and ligand-deficient 1:1 compounds Magnetic measurements were performed, which reveal different Magnetic properties: The 1:2 compounds show a ferroMagnetic and the 1:1 compounds an antiferroMagnetic ordering at lower temperatures.
T Scopigno - One of the best experts on this subject based on the ideXlab platform.
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probing ultrafast photo induced dynamics of the exchange energy in a heisenberg antiferromagnet
Nature Photonics, 2015Co-Authors: Giovanni Batignani, D Bossini, N Di Palo, Carino Ferrante, E Pontecorvo, G Cerullo, A V Kimel, T ScopignoAbstract:Femtosecond stimulated Raman experiments on the antiferroMagnetic system KNiF3 are implemented to understand how the exchange interaction — a crucial interaction that rules Magnetic Phenomena — is influenced by ultrafast optical excitation.
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Probing ultrafast photo-induced dynamics of the exchange energy in a Heisenberg antiferromagnet
Nature Photonics, 2015Co-Authors: Giovanni Batignani, D Bossini, N Di Palo, Carino Ferrante, E Pontecorvo, G Cerullo, A V Kimel, T ScopignoAbstract:Femtosecond stimulated Raman experiments on the antiferroMagnetic system KNiF_3 are implemented to understand how the exchange interaction — a crucial interaction that rules Magnetic Phenomena — is influenced by ultrafast optical excitation. Manipulating the macroscopic phases of solids using ultrashort light pulses has resulted in spectacular Phenomena, including metal–insulator transitions^ 1 , 2 , 3 , superconductivity^ 4 and subpicosecond modification of Magnetic order^ 5 . The development of this research area strongly depends on the understanding and optical control of fundamental interactions in condensed matter, in particular the exchange interaction. However, disentangling the timescales relevant for the contributions of the exchange interaction and spin dynamics to the exchange energy, E _ex, is a challenge. Here, we introduce femtosecond stimulated Raman scattering to unravel the ultrafast photo-induced dynamics of Magnetic excitations at the edge of the Brillouin zone. We find that femtosecond laser excitation of the antiferromagnet KNiF_3 triggers a spectral shift of the two-magnon line, the energy of which is proportional to E _ex. By unravelling the photo-induced modification of the two-magnon line frequency from a dominating nonlinear optical effect, we find that E _ex is increased by the electroMagnetic stimulus.
Subhasis Ghosh - One of the best experts on this subject based on the ideXlab platform.
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multiple phases with a tricritical point and a lifshitz point in the skyrmion host cu 2 oseo 3
Physical Review B, 2019Co-Authors: Harish Chandr Chauhan, Birendra Kumar, Jeetendra Kumar Tiwari, Subhasis GhoshAbstract:Magnetic skyrmions, topologically stable spin swirling objects, have attracted a great interest due to their potential applications in future spintronics and ultrahigh dense Magnetic memory devices. Existence of a skyrmion phase as well as first- and second-order phase transitions make ${\mathrm{Cu}}_{2}{\mathrm{OSeO}}_{3}$ a promising candidate for investigating complex Magnetic Phenomena. Here, we report that both first- and second-order Magnetic phase transitions are responsible in determining the phase diagram with at least two multicritical points in ${\mathrm{Cu}}_{2}{\mathrm{OSeO}}_{3}$. A fluctuation-induced first-order transition is realized as a precursor for the skyrmion phase over a small window of temperature and Magnetic field. The evolution of isothermal entropy at the phase transition provides evidence for a tricritical point. Furthermore, the existence of commensurate and incommensurate phases along with the coexistence of three second-order phase transitions provide evidence for the existence of a Lifshitz point.
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multiple phases with tricritical point and lifshitz point in skyrmion host cu _2 oseo _3
arXiv: Strongly Correlated Electrons, 2019Co-Authors: Harish Chandr Chauhan, Birendra Kumar, Jeetendra Kumar Tiwari, Subhasis GhoshAbstract:Magnetic skyrmions, a topologically stable spin swirling object, have attracted a great interest due to their potential applications in future spintronics and ultra high dense Magnetic memory devices. Cu$_2$OSeO$_3$ is only known insulating chiral helimagnet with multiple phases including skyrmion phase. Existence of skyrmion phase as well as first and second order phase transitions make Cu$_2$OSeO$_3$ a promissing candidate for investigating complex Magnetic Phenomena. Here, we report that both first and second order Magnetic phase transitions are responsible in determining the phase diagram with atleast two multicritical point in Cu$_2$OSeO$_3$. Fluctuation-induced first order transition is realized as a precursor for skyrmion phase over a small window of temperature of Magnetic field. The evolution of field dependent entropy at the phase transition provides the evidence for tricritical point. Furthermore, existence of commensurate and incommensurate phases, alongwith co-existence of three second order phase transitions provide evidence for the existence of Lifshitz point.
Giovanni Batignani - One of the best experts on this subject based on the ideXlab platform.
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probing ultrafast photo induced dynamics of the exchange energy in a heisenberg antiferromagnet
Nature Photonics, 2015Co-Authors: Giovanni Batignani, D Bossini, N Di Palo, Carino Ferrante, E Pontecorvo, G Cerullo, A V Kimel, T ScopignoAbstract:Femtosecond stimulated Raman experiments on the antiferroMagnetic system KNiF3 are implemented to understand how the exchange interaction — a crucial interaction that rules Magnetic Phenomena — is influenced by ultrafast optical excitation.
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Probing ultrafast photo-induced dynamics of the exchange energy in a Heisenberg antiferromagnet
Nature Photonics, 2015Co-Authors: Giovanni Batignani, D Bossini, N Di Palo, Carino Ferrante, E Pontecorvo, G Cerullo, A V Kimel, T ScopignoAbstract:Femtosecond stimulated Raman experiments on the antiferroMagnetic system KNiF_3 are implemented to understand how the exchange interaction — a crucial interaction that rules Magnetic Phenomena — is influenced by ultrafast optical excitation. Manipulating the macroscopic phases of solids using ultrashort light pulses has resulted in spectacular Phenomena, including metal–insulator transitions^ 1 , 2 , 3 , superconductivity^ 4 and subpicosecond modification of Magnetic order^ 5 . The development of this research area strongly depends on the understanding and optical control of fundamental interactions in condensed matter, in particular the exchange interaction. However, disentangling the timescales relevant for the contributions of the exchange interaction and spin dynamics to the exchange energy, E _ex, is a challenge. Here, we introduce femtosecond stimulated Raman scattering to unravel the ultrafast photo-induced dynamics of Magnetic excitations at the edge of the Brillouin zone. We find that femtosecond laser excitation of the antiferromagnet KNiF_3 triggers a spectral shift of the two-magnon line, the energy of which is proportional to E _ex. By unravelling the photo-induced modification of the two-magnon line frequency from a dominating nonlinear optical effect, we find that E _ex is increased by the electroMagnetic stimulus.