{"id":{"repo_id":"aachen","oai_identifier":"oai:publications.rwth-aachen.de:50831"},"canonical_url":"https://search.dev.ndltd.org/etd/aachen/oai:publications.rwth-aachen.de:50831","repository":{"repo_id":"aachen","name":"RWTH Aachen University","base_url":"https://publications.rwth-aachen.de/oai2d"},"display":{"title":"Peculiarities of crystal and magnetic structures of synthetic Co-olivine, Co 2 SiO 4","abstract":"Compounds of the chemical formula M2SiO4 with olivine-type structure are of fundamental importance for geologists and mineralogists because of the presence of a huge amount of the olivines in the earth's upper mantle. Here, M is mainly Fe, Mg and Mn with small amounts of Ni, Ca, Co and Zn in mixed crystals. Many studies provided abundant data on the olivine-type oxides, especially at or above room temperature and at high pressure. However, there is still a lack of information on the magnetic properties and the thermal evolution of the crystal structure below room temperature for some olivines. One of the less studied olivine-type silicates is the synthetic cobalt olivine, Co2SiO4. The main goal of the present study is to determine precisely the changes in both the crystal and magnetic structures of Co2SiO4 in a wide temperature range from 2.5 K up to 500 K. Synthetic Co2SiO4 has an orthorhombic crystal structure (space group Pnma, No. 62) and shows magnetic ordering below 50 K. Both single-crystal (2.5 K - 300 K) and powder (5 K - 500 K) neutron diffraction were applied to determine precise crystal structure parameters. Lattice parameters were also determined by means of both high-resolution synchrotron and laboratory X-ray powder diffraction measurements between 15 K and 300 K. The orthorhombic symmetry with space group Pnma was found to be retained in the temperature range from 2.5 K up to 500 K. In order to parameterize the cell parameters of Co2SiO4 the molar specific heat was measured and fitted taking into account the Debye-Einstein lattice contribution, the magnetic part and the Schottky contribution. The unit cell volume was then fitted based on the specific heat data. There is a clear evidence of an anomalous thermal expansion related to the magnetic phase transition. This anomaly in the lattice parameters and the unit cell volume can be attributed to magnetostriction. Detailed symmetry analysis of the magnetic structure shows that it corresponds to the magnetic (Shubnikov) group Pnma, which allows the antiferromagnetic configuration (Gx,Cy,Az) for the 4a site with inversion symmetry (Co1 position) and (0,Cy,0) for the 4c site with mirror symmetry (Co2 position). Magnetic anisotropy was studied by fitting the observed susceptibility curves above Neel temperature to the Curie-Weiss law, thus giving the Curie-Weiss temperatures and effective magnetic moments. The magnetic moments from the neutron diffraction data were found to be 3.86(5) Bohr magneton and 3.37(4) Bohr magneton for Co1 and Co2, respectively. These values are much higher than the spin-only one for high-spin Co2+ (3 Bohr magneton) indicating the orbital contribution. This is in agreement with both magnetic susceptibility and X-ray magnetic circular dichroism measurements. The accurate analysis of the neutron diffraction data as a function of temperature shows no change in the spin configuration in the whole temperature range of the magnetically ordered state. The magnetic structure of Co2SiO4 has also been studied by means of polarized neutron diffraction on a single crystal. Measurements were made at temperatures of 70 K and 150 K in an external magnetic field of 7 T parallel to the b axis. This study of the magnetization induced by an applied field above T_N shows an anisotropy which is found to be rather small at high temperatures but becomes very strongly enhanced when approaching the ordering temperature. The refinement also revealed a non-negligible amount of magnetic moment on the three different oxygen positions which was interpreted as a delocalization of the magnetic moment from Co2+ towards the neighbouring O due to the superexchange coupling. The electron-density distribution in Co2SiO4 was studied by means of singlecrystal synchrotron X-ray diffraction measurements at 12 K, 40 K and 300 K. The data were analysed using both Fourier and maximum-entropy methods. A tendency to an elongation of the valence electron density along the direction of the magnetic moments with decrease of temperature was found in agreement with an elongation of the magnetic ellipsoids obtained from polarized neutron flipping-ratio measurements. The assumption of a partly covalent character of the Co-O bonding was confirmed.","abstract_html":"Compounds of the chemical formula M2SiO4 with olivine-type structure are of fundamental importance for geologists and mineralogists because of the presence of a huge amount of the olivines in the earth's upper mantle. Here, M is mainly Fe, Mg and Mn with small amounts of Ni, Ca, Co and Zn in mixed crystals. Many studies provided abundant data on the olivine-type oxides, especially at or above room temperature and at high pressure. However, there is still a lack of information on the magnetic properties and the thermal evolution of the crystal structure below room temperature for some olivines. One of the less studied olivine-type silicates is the synthetic cobalt olivine, Co2SiO4. The main goal of the present study is to determine precisely the changes in both the crystal and magnetic structures of Co2SiO4 in a wide temperature range from 2.5 K up to 500 K. Synthetic Co2SiO4 has an orthorhombic crystal structure (space group Pnma, No. 62) and shows magnetic ordering below 50 K. Both single-crystal (2.5 K - 300 K) and powder (5 K - 500 K) neutron diffraction were applied to determine precise crystal structure parameters. Lattice parameters were also determined by means of both high-resolution synchrotron and laboratory X-ray powder diffraction measurements between 15 K and 300 K. The orthorhombic symmetry with space group Pnma was found to be retained in the temperature range from 2.5 K up to 500 K. In order to parameterize the cell parameters of Co2SiO4 the molar specific heat was measured and fitted taking into account the Debye-Einstein lattice contribution, the magnetic part and the Schottky contribution. The unit cell volume was then fitted based on the specific heat data. There is a clear evidence of an anomalous thermal expansion related to the magnetic phase transition. This anomaly in the lattice parameters and the unit cell volume can be attributed to magnetostriction. Detailed symmetry analysis of the magnetic structure shows that it corresponds to the magnetic (Shubnikov) group Pnma, which allows the antiferromagnetic configuration (Gx,Cy,Az) for the 4a site with inversion symmetry (Co1 position) and (0,Cy,0) for the 4c site with mirror symmetry (Co2 position). Magnetic anisotropy was studied by fitting the observed susceptibility curves above Neel temperature to the Curie-Weiss law, thus giving the Curie-Weiss temperatures and effective magnetic moments. The magnetic moments from the neutron diffraction data were found to be 3.86(5) Bohr magneton and 3.37(4) Bohr magneton for Co1 and Co2, respectively. These values are much higher than the spin-only one for high-spin Co2+ (3 Bohr magneton) indicating the orbital contribution. This is in agreement with both magnetic susceptibility and X-ray magnetic circular dichroism measurements. The accurate analysis of the neutron diffraction data as a function of temperature shows no change in the spin configuration in the whole temperature range of the magnetically ordered state. The magnetic structure of Co2SiO4 has also been studied by means of polarized neutron diffraction on a single crystal. Measurements were made at temperatures of 70 K and 150 K in an external magnetic field of 7 T parallel to the b axis. This study of the magnetization induced by an applied field above T_N shows an anisotropy which is found to be rather small at high temperatures but becomes very strongly enhanced when approaching the ordering temperature. The refinement also revealed a non-negligible amount of magnetic moment on the three different oxygen positions which was interpreted as a delocalization of the magnetic moment from Co2+ towards the neighbouring O due to the superexchange coupling. The electron-density distribution in Co2SiO4 was studied by means of singlecrystal synchrotron X-ray diffraction measurements at 12 K, 40 K and 300 K. The data were analysed using both Fourier and maximum-entropy methods. A tendency to an elongation of the valence electron density along the direction of the magnetic moments with decrease of temperature was found in agreement with an elongation of the magnetic ellipsoids obtained from polarized neutron flipping-ratio measurements. The assumption of a partly covalent character of the Co-O bonding was confirmed.","abstract_has_math":false,"creators":["Sazonov, Andrew P."],"institution":"Hut","degree_name":null,"degree_level":null,"degree_discipline":null,"degree_department":null,"school":null,"contributors":["Heger, Gernot"],"advisors":[],"committee_chairs":[],"committee_members":[],"year":2009,"date_issued":"2009","date_published":"2009","updated_at":"2026-07-30T19:40:25Z","subjects":["info:eu-repo/classification/ddc/530","Olivin","Magnetostriktion","Magnetismus","Neutronendiffraktometrie","Röntgendiffraktometrie","Magnetischer Röntgenzirkulardichroismus","Wärmekapazität","Einkristall","Keramikpulver","Physik","olivine","magnetostriction","antiferromagnetism","neuton diffraction","X-ray diffraction","magnetic circular dichroism","specific heat","single crystal","powder"],"languages":["eng"],"rights":["info:eu-repo/semantics/openAccess"],"rights_urls":[],"identifier_entries":[{"key":"dc:identifier","label":"Identifier","values":["https://publications.rwth-aachen.de/search?p=id:%22RWTH-CONV-113355%22"],"render_values":[{"text":"https://publications.rwth-aachen.de/search?p=id:%22RWTH-CONV-113355%22","href":"https://publications.rwth-aachen.de/search?p=id:%22RWTH-CONV-113355%22","code":true}]}]},"links":{"outbound_url":"https://publications.rwth-aachen.de/record/50831","outbound_label":"Repository record","outbound_source":"dc:identifier"},"source_record":{"url":"https://publications.rwth-aachen.de/oai2d?verb=GetRecord&metadataPrefix=oai_dc&identifier=oai%3Apublications.rwth-aachen.de%3A50831","prefix":"oai_dc"},"metadata_groups":[{"id":"people","label":"People","entries":[{"key":"dc:contributor","label":"Contributor","values":["Heger, Gernot"]},{"key":"dc:creator","label":"Author","values":["Sazonov, Andrew P."]}]},{"id":"academic_context","label":"Academic Context","entries":[{"key":"dc:coverage","label":"Dc Coverage","values":["DE"]},{"key":"dc:date","label":"Dc Date","values":["2009"]},{"key":"dc:publisher","label":"Institution","values":["Hut"]},{"key":"dc:relation","label":"Dc Relation","values":["info:eu-repo/semantics/altIdentifier/urn/urn:nbn:de:hbz:82-opus-29686","info:eu-repo/semantics/altIdentifier/isbn/978-3-86853-198-5"]},{"key":"dc:type","label":"Dc Type","values":["info:eu-repo/semantics/doctoralThesis","info:eu-repo/semantics/publishedVersion"]}]},{"id":"subjects_keywords","label":"Subjects and Keywords","entries":[{"key":"dc:subject","label":"Dc Subject","values":["info:eu-repo/classification/ddc/530","Olivin","Magnetostriktion","Magnetismus","Neutronendiffraktometrie","Röntgendiffraktometrie","Magnetischer Röntgenzirkulardichroismus","Wärmekapazität","Einkristall","Keramikpulver","Physik","olivine","magnetostriction","antiferromagnetism","neuton diffraction","X-ray diffraction","magnetic circular dichroism","specific heat","single crystal","powder"]}]},{"id":"language_rights","label":"Language and Rights","entries":[{"key":"dc:language","label":"Dc Language","values":["eng"]},{"key":"dc:rights","label":"Dc Rights","values":["info:eu-repo/semantics/openAccess"]}]},{"id":"identifiers","label":"Identifiers","entries":[{"key":"dc:identifier","label":"Identifier","values":["https://publications.rwth-aachen.de/record/50831","https://publications.rwth-aachen.de/search?p=id:%22RWTH-CONV-113355%22"]}]},{"id":"additional","label":"Additional Metadata","entries":[{"key":"dc:description","label":"Description","values":["Compounds of the chemical formula M2SiO4 with olivine-type structure are of fundamental importance for geologists and mineralogists because of the presence of a huge amount of the olivines in the earth's upper mantle. Here, M is mainly Fe, Mg and Mn with small amounts of Ni, Ca, Co and Zn in mixed crystals. Many studies provided abundant data on the olivine-type oxides, especially at or above room temperature and at high pressure. However, there is still a lack of information on the magnetic properties and the thermal evolution of the crystal structure below room temperature for some olivines. One of the less studied olivine-type silicates is the synthetic cobalt olivine, Co2SiO4. The main goal of the present study is to determine precisely the changes in both the crystal and magnetic structures of Co2SiO4 in a wide temperature range from 2.5 K up to 500 K. Synthetic Co2SiO4 has an orthorhombic crystal structure (space group Pnma, No. 62) and shows magnetic ordering below 50 K. Both single-crystal (2.5 K - 300 K) and powder (5 K - 500 K) neutron diffraction were applied to determine precise crystal structure parameters. Lattice parameters were also determined by means of both high-resolution synchrotron and laboratory X-ray powder diffraction measurements between 15 K and 300 K. The orthorhombic symmetry with space group Pnma was found to be retained in the temperature range from 2.5 K up to 500 K. In order to parameterize the cell parameters of Co2SiO4 the molar specific heat was measured and fitted taking into account the Debye-Einstein lattice contribution, the magnetic part and the Schottky contribution. The unit cell volume was then fitted based on the specific heat data. There is a clear evidence of an anomalous thermal expansion related to the magnetic phase transition. This anomaly in the lattice parameters and the unit cell volume can be attributed to magnetostriction. Detailed symmetry analysis of the magnetic structure shows that it corresponds to the magnetic (Shubnikov) group Pnma, which allows the antiferromagnetic configuration (Gx,Cy,Az) for the 4a site with inversion symmetry (Co1 position) and (0,Cy,0) for the 4c site with mirror symmetry (Co2 position). Magnetic anisotropy was studied by fitting the observed susceptibility curves above Neel temperature to the Curie-Weiss law, thus giving the Curie-Weiss temperatures and effective magnetic moments. The magnetic moments from the neutron diffraction data were found to be 3.86(5) Bohr magneton and 3.37(4) Bohr magneton for Co1 and Co2, respectively. These values are much higher than the spin-only one for high-spin Co2+ (3 Bohr magneton) indicating the orbital contribution. This is in agreement with both magnetic susceptibility and X-ray magnetic circular dichroism measurements. The accurate analysis of the neutron diffraction data as a function of temperature shows no change in the spin configuration in the whole temperature range of the magnetically ordered state. The magnetic structure of Co2SiO4 has also been studied by means of polarized neutron diffraction on a single crystal. Measurements were made at temperatures of 70 K and 150 K in an external magnetic field of 7 T parallel to the b axis. This study of the magnetization induced by an applied field above T_N shows an anisotropy which is found to be rather small at high temperatures but becomes very strongly enhanced when approaching the ordering temperature. The refinement also revealed a non-negligible amount of magnetic moment on the three different oxygen positions which was interpreted as a delocalization of the magnetic moment from Co2+ towards the neighbouring O due to the superexchange coupling. The electron-density distribution in Co2SiO4 was studied by means of singlecrystal synchrotron X-ray diffraction measurements at 12 K, 40 K and 300 K. The data were analysed using both Fourier and maximum-entropy methods. A tendency to an elongation of the valence electron density along the direction of the magnetic moments with decrease of temperature was found in agreement with an elongation of the magnetic ellipsoids obtained from polarized neutron flipping-ratio measurements. The assumption of a partly covalent character of the Co-O bonding was confirmed."]},{"key":"dc:source","label":"Dc Source","values":["München : Hut XII, 138 S. : Ill., graph. Darst. (2009). = Zugl.: Aachen, Techn. Hochsch., Diss., 2009"]},{"key":"dc:title","label":"Title","values":["Peculiarities of crystal and magnetic structures of synthetic Co-olivine, Co 2 SiO 4"]}]}],"canonical_facts":{"dc:contributor":["Heger, Gernot"],"dc:coverage":["DE"],"dc:creator":["Sazonov, Andrew P."],"dc:date":["2009"],"dc:description":["Compounds of the chemical formula M2SiO4 with olivine-type structure are of fundamental importance for geologists and mineralogists because of the presence of a huge amount of the olivines in the earth's upper mantle. Here, M is mainly Fe, Mg and Mn with small amounts of Ni, Ca, Co and Zn in mixed crystals. Many studies provided abundant data on the olivine-type oxides, especially at or above room temperature and at high pressure. However, there is still a lack of information on the magnetic properties and the thermal evolution of the crystal structure below room temperature for some olivines. One of the less studied olivine-type silicates is the synthetic cobalt olivine, Co2SiO4. The main goal of the present study is to determine precisely the changes in both the crystal and magnetic structures of Co2SiO4 in a wide temperature range from 2.5 K up to 500 K. Synthetic Co2SiO4 has an orthorhombic crystal structure (space group Pnma, No. 62) and shows magnetic ordering below 50 K. Both single-crystal (2.5 K - 300 K) and powder (5 K - 500 K) neutron diffraction were applied to determine precise crystal structure parameters. Lattice parameters were also determined by means of both high-resolution synchrotron and laboratory X-ray powder diffraction measurements between 15 K and 300 K. The orthorhombic symmetry with space group Pnma was found to be retained in the temperature range from 2.5 K up to 500 K. In order to parameterize the cell parameters of Co2SiO4 the molar specific heat was measured and fitted taking into account the Debye-Einstein lattice contribution, the magnetic part and the Schottky contribution. The unit cell volume was then fitted based on the specific heat data. There is a clear evidence of an anomalous thermal expansion related to the magnetic phase transition. This anomaly in the lattice parameters and the unit cell volume can be attributed to magnetostriction. Detailed symmetry analysis of the magnetic structure shows that it corresponds to the magnetic (Shubnikov) group Pnma, which allows the antiferromagnetic configuration (Gx,Cy,Az) for the 4a site with inversion symmetry (Co1 position) and (0,Cy,0) for the 4c site with mirror symmetry (Co2 position). Magnetic anisotropy was studied by fitting the observed susceptibility curves above Neel temperature to the Curie-Weiss law, thus giving the Curie-Weiss temperatures and effective magnetic moments. The magnetic moments from the neutron diffraction data were found to be 3.86(5) Bohr magneton and 3.37(4) Bohr magneton for Co1 and Co2, respectively. These values are much higher than the spin-only one for high-spin Co2+ (3 Bohr magneton) indicating the orbital contribution. This is in agreement with both magnetic susceptibility and X-ray magnetic circular dichroism measurements. The accurate analysis of the neutron diffraction data as a function of temperature shows no change in the spin configuration in the whole temperature range of the magnetically ordered state. The magnetic structure of Co2SiO4 has also been studied by means of polarized neutron diffraction on a single crystal. Measurements were made at temperatures of 70 K and 150 K in an external magnetic field of 7 T parallel to the b axis. This study of the magnetization induced by an applied field above T_N shows an anisotropy which is found to be rather small at high temperatures but becomes very strongly enhanced when approaching the ordering temperature. The refinement also revealed a non-negligible amount of magnetic moment on the three different oxygen positions which was interpreted as a delocalization of the magnetic moment from Co2+ towards the neighbouring O due to the superexchange coupling. The electron-density distribution in Co2SiO4 was studied by means of singlecrystal synchrotron X-ray diffraction measurements at 12 K, 40 K and 300 K. The data were analysed using both Fourier and maximum-entropy methods. A tendency to an elongation of the valence electron density along the direction of the magnetic moments with decrease of temperature was found in agreement with an elongation of the magnetic ellipsoids obtained from polarized neutron flipping-ratio measurements. The assumption of a partly covalent character of the Co-O bonding was confirmed."],"dc:identifier":["https://publications.rwth-aachen.de/record/50831","https://publications.rwth-aachen.de/search?p=id:%22RWTH-CONV-113355%22"],"dc:language":["eng"],"dc:publisher":["Hut"],"dc:relation":["info:eu-repo/semantics/altIdentifier/urn/urn:nbn:de:hbz:82-opus-29686","info:eu-repo/semantics/altIdentifier/isbn/978-3-86853-198-5"],"dc:rights":["info:eu-repo/semantics/openAccess"],"dc:source":["München : Hut XII, 138 S. : Ill., graph. Darst. (2009). = Zugl.: Aachen, Techn. Hochsch., Diss., 2009"],"dc:subject":["info:eu-repo/classification/ddc/530","Olivin","Magnetostriktion","Magnetismus","Neutronendiffraktometrie","Röntgendiffraktometrie","Magnetischer Röntgenzirkulardichroismus","Wärmekapazität","Einkristall","Keramikpulver","Physik","olivine","magnetostriction","antiferromagnetism","neuton diffraction","X-ray diffraction","magnetic circular dichroism","specific heat","single crystal","powder"],"dc:title":["Peculiarities of crystal and magnetic structures of synthetic Co-olivine, Co 2 SiO 4"],"dc:type":["info:eu-repo/semantics/doctoralThesis","info:eu-repo/semantics/publishedVersion"]},"updated_at":"2026-07-30T19:40:25Z"}