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Mössbauer Spectroscopy of Meteoritic and Synthetic Fe-Ni Alloys
Uppsala University, Teknisk-naturvetenskapliga vetenskapsområdet, Earth Sciences, Department of Earth Sciences.
2004 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

This thesis reports on the results of investigating Fe-containing minerals in meteorites, with focus on Fe-Ni minerals and their magnetic properties, along with some synthetic Fe-Ni analogues. The New Halfa meteorite, which fell in Sudan 1994, has been studied using Mössbauer spectroscopy, X-ray diffraction, and electron microprobe analysis techniques, and classified as an ordinary L-type chondrite of petrologic type 4. Mössbauer spectra of taenite-enriched samples from the metal particles of the New Halfa (L4) and Al Kidirate (H6) meteorites identify the following γ (fcc) Fe-Ni phases: the ferromagnetic atomically ordered taenite (tetrataenite) with ~ 50 at % Ni, the ferromagnetic disordered taenite with ~ 50 at % Ni, the low-Ni (~ 25 at %) paramagnetic taenite (antitaenite). The presence of the superstructure of tetrataenite is confirmed by synchrotron X-ray diffraction.

Fe-rich γ (fcc) Fe-Ni alloys with compositions Fe79Ni21, Fe76Ni24, and Fe73Ni27, which serve as synthetic analogues of antitaenite, are prepared by mechanical alloying and subsequent annealing at 650 °C. The Mössbauer results indicate that these alloys are inhomogeneous and contain a high moment (HM) ferromagnetic Ni-rich phase (> 30 at % Ni) and a low moment (LM) paramagnetic Fe-rich phase, which orders antiferromagnetically at low temperature. The coexistence of these phases is attributed to phase segregation occurring on short range, probably nanometer scale, consistent with the Fe-Ni phase diagram below 400 °C where there is a miscibility gap associated with a spinodal decomposition in alloys with < 50 at % Ni.

The combined high field Mössbauer spectroscopy and SQUID magnetometry results on these alloys at room temperature indicate large induced local magnetic moments in the paramagnetic part of the sample, which increases with increasing the Ni content. The results, when compared with the high field Mössbauer results on antitaenite from the metal particle of Al Kidirate and New Halfa meteorites may be used to estimate the Ni content of antitaenite in meteorites.

High pressure 57Fe Mössbauer spectroscopy measurements up to ~ 41 GPa have been carried out at room temperature using the diamond anvil cell (DAC) technique in order to investigate the magnetic properties of γ (fcc) 57Fe53Ni47 alloy. The results indicate a pressure induced Invar effect at ~ 7 GPa and a non-magnetic or paramagnetic state above 20 GPa, demonstrating the volume dependence of the magnetic moment of γ (fcc) Fe-Ni alloys.

Place, publisher, year, edition, pages
Uppsala: Acta Universitatis Upsaliensis , 2004. , p. 39
Series
Comprehensive Summaries of Uppsala Dissertations from the Faculty of Science and Technology, ISSN 1104-232X ; 928
Keywords [en]
Earth sciences, Meteorites, Tetrataenite, Antitaenite, Mössbauer spectroscopy, Mechanical alloying, Fe-Ni alloys, High pressure
Keywords [sv]
Geovetenskap
National Category
Earth and Related Environmental Sciences
Research subject
Mineral Chemistry, Petrology and Tectonics
Identifiers
URN: urn:nbn:se:uu:diva-3969ISBN: 91-554-5854-8 (print)OAI: oai:DiVA.org:uu-3969DiVA, id: diva2:163963
Public defence
2004-02-12, Axel Hambergsalen, Geocentrum, Villavägen 16, Uppsala, 10:00
Opponent
Supervisors
Available from: 2004-01-15 Created: 2004-01-15Bibliographically approved
List of papers
1. Mössbauer spectroscopy, X-ray diffraction and electron microprobe analysis of the New Halfa meteorite
Open this publication in new window or tab >>Mössbauer spectroscopy, X-ray diffraction and electron microprobe analysis of the New Halfa meteorite
1997 In: Meteoritics and Planetary Science, Vol. 32, p. 373-375Article in journal (Refereed) Published
Identifiers
urn:nbn:se:uu:diva-91276 (URN)
Available from: 2004-01-15 Created: 2004-01-15Bibliographically approved
2. Mössbauer studies on the metallic phases of Al Kidirate and New Halfa Meteorites
Open this publication in new window or tab >>Mössbauer studies on the metallic phases of Al Kidirate and New Halfa Meteorites
Show others...
2002 In: Hyperfine Interactions C, Vol. 5, p. 375-378Article in journal (Refereed) Published
Identifiers
urn:nbn:se:uu:diva-91277 (URN)
Available from: 2004-01-15 Created: 2004-01-15Bibliographically approved
3. Coexisting antiferromagnetism and ferromagnetism in mechanically alloyed Fe-rich Fe-Ni alloys: Implications regarding the Fe-Ni phase diagram below 400 °C
Open this publication in new window or tab >>Coexisting antiferromagnetism and ferromagnetism in mechanically alloyed Fe-rich Fe-Ni alloys: Implications regarding the Fe-Ni phase diagram below 400 °C
2004 (English)In: Journal of Magnetism and Magnetic Materials, ISSN 0304-8853, E-ISSN 1873-4766, Vol. 280, no 2-3, p. 395-403Article in journal (Refereed) Published
Abstract [en]

Fe–Ni alloys below the Invar region with compositions Fe100−xNix (x=21, 24, and 27 at%) were prepared by high-energy ball milling technique (mechanical alloying). The as-milled samples, characterized by X-ray diffraction and Mössbauer spectroscopy, contain a mixture of α (BCC) and γ (FCC) phases, whereas the samples annealed at 650°C for 0.5 h show a single γ (FCC) phase displaying a single line Mössbauer spectrum at room temperature (RT). At low temperature, the Mössbauer spectra of annealed Fe76Ni24 and Fe73Ni27 alloys show the existence of a magnetically split pattern together with a broad singlet, which are ascribed to a high-moment ferromagnetic Ni-rich phase and a low-moment Fe-rich phase, respectively. The Fe-rich phase in annealed Fe76Ni24 alloy, which is paramagnetic at RT, undergoes antiferromagnetic ordering at ∼40 K, estimated from the dramatic line broadening of its spectrum, giving rise to a small hyperfine field (e.g. ∼2 T at 6 K). The coexistence of these phases is attributed to phase segregation occurring in these alloys as a result of enhanced atomic diffusion. The stability of these alloys towards martensitic (FCC→BCC) transformation at low temperatures is discussed in connection with the Fe–Ni phase diagram below 400°C.

National Category
Natural Sciences
Identifiers
urn:nbn:se:uu:diva-91278 (URN)10.1016/j.jmmm.2004.03.036 (DOI)
Available from: 2004-01-15 Created: 2004-01-15 Last updated: 2017-12-14Bibliographically approved
4. Field induced local magnetic moments in gamma-fcc Fe-Ni anti-Invar alloys
Open this publication in new window or tab >>Field induced local magnetic moments in gamma-fcc Fe-Ni anti-Invar alloys
2004 (English)In: Journal of Magnetism and Magnetic Materials, ISSN 0304-8853, E-ISSN 1873-4766, Vol. 280, p. 243-250Article in journal (Refereed) Published
Abstract [en]

Mössbauer spectroscopy in longitudinal external fields (up to 7 T) and SQUID magnetometry (up to 5 T)measurements have been carried out on mechanically alloyed (MA) g (FCC) Fe100xNix (x ¼ 21; 24, and 27 at%) alloysat room temperature. The zero-field M.ossbauer spectra of these alloys show only singlets. The high field M.ossbauerresults indicate that large amounts of the material is in the paramagnetic state, giving rise to two spectral componentswith their effective fields almost linearly depend on the external field, but with slopes that are smaller than unity. The infieldM.ossbauer spectra of the x ¼ 27 at% alloy show an additional component with a hyperfine field of E21 T, whichis attributed to Ni-rich (>30 at% Ni) clusters (domains) of ferromagnetically ordered HM phase that behavessuperparamagnetically at room temperature and shows a non-linear character in the magnetization (M–H) curves atlow fields. This HM phase is also present in the x ¼ 21 and 24 at% samples but with smaller amounts. The resultssuggest induced hyperfine fields and hence induced moments in the paramagnetic components, which increases withincreasing Ni contents. Taenite-enriched samples from the metal particles of two stony meteorites, Al Kidirate (H6)and New Halfa (L4), are also studied by high field M.ossbauer spectroscopy and the results are compared to that ofMA samples.

Keywords
Mössbauer spectroscopy; External field; Magnetization; Fe–Ni alloys; Antitaenite
National Category
Natural Sciences
Identifiers
urn:nbn:se:uu:diva-91279 (URN)
Available from: 2004-01-15 Created: 2004-01-15 Last updated: 2017-12-14Bibliographically approved
5. Non-magnetic stainless steels reinvestigated: A small effective field component in external magnetic fields
Open this publication in new window or tab >>Non-magnetic stainless steels reinvestigated: A small effective field component in external magnetic fields
2004 (English)In: Hyperfine Interactions, ISSN 0304-3843, E-ISSN 1572-9540, Vol. 156/157, p. 151-155Article in journal (Refereed) Published
Abstract [en]

Three standard non-magnetic stainl ess steels of composition (wt%) Fe 70 Cr 19 Ni 11 , Fe 70 Cr 17 Ni 13 and Fe 69 Cr 18 . 5 Ni 10 . 3 Mn 1 . 8 Ti 0 . 4 have been investigated by Mössbauer spectroscopy (5–295 K and in external fields 7 T at room temperature) and ma gnetization measurements (10– 300 K) using a SQUID magnetometer. There are indications of a field induced ferromagnetic inter- action in the samples at room temperature

Keywords
stainless steel, external field, field induced ferromagnetism
National Category
Natural Sciences
Identifiers
urn:nbn:se:uu:diva-91280 (URN)
Available from: 2004-01-15 Created: 2004-01-15 Last updated: 2017-12-14Bibliographically approved
6. High pressure Mössbauer studies on fcc Fe53Ni47 alloy
Open this publication in new window or tab >>High pressure Mössbauer studies on fcc Fe53Ni47 alloy
2004 (English)In: Hyperfine Interactions, ISSN 0304-3843, E-ISSN 1572-9540, Vol. 156, p. 394-, article id 389Article in journal (Refereed) Published
National Category
Natural Sciences
Identifiers
urn:nbn:se:uu:diva-91281 (URN)10.1007/978-1-4020-2852-6_59 (DOI)
Available from: 2004-01-15 Created: 2004-01-15 Last updated: 2017-12-14Bibliographically approved

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