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- Abdu, Yassir Ahmed Mohamed, 1966-
(författare)
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Mössbauer Spectroscopy of Meteoritic and Synthetic Fe-Ni Alloys
- 2004
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- 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.
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| 2. |
- Abdu, Yassir, et al.
(författare)
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Coexisting antiferromagnetism and ferromagnetism in mechanically alloyed Fe-rich Fe-Ni alloys : Implications regarding the Fe-Ni phase diagram below 400 °C
- 2004
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Ingår i: Journal of Magnetism and Magnetic Materials. - : Elsevier BV. - 0304-8853 .- 1873-4766. ; 280:2-3, s. 395-403
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Tidskriftsartikel (refereegranskat)abstract
- 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.
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| 3. |
- Abdu, Yassir, et al.
(författare)
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Field induced local magnetic moments in gamma-fcc Fe-Ni anti-Invar alloys
- 2004
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Ingår i: Journal of Magnetism and Magnetic Materials. - 0304-8853 .- 1873-4766. ; 280, s. 243-250
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Tidskriftsartikel (refereegranskat)abstract
- 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.
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| 9. |
- Bedin, Michele, 1984-, et al.
(författare)
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Dinuclear iron and manganese complex with an asymmetric ligand
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Annan publikation (övrigt vetenskapligt/konstnärligt)abstract
- Three complexes using the same asymmetric and dinucleating ligand DPCPMP (2-(N-(3-((bis((pyridin-2-yl)methyl)amino)methyl)-2-hydroxy-5-methylbenzyl)-N-((pyridin-2-yl)methyl)amino acetic acid) have been synthesised. The ligand contains one pocket with three nitrogen donors and another pocket with two nitrogen donors and one oxygen donor. The complexes were containing two iron ions ([Fe2(DPCPMP)(CH3COO)2]), two manganese ions ([Mn2(DPCPMP)(CH3COO)2]) or one iron and one manganese ion ([FeMn(DPCPMP)(CH3COO)2]) mimicing the metal content in the three different subclasses of class I ribonucleotide reductases. The asymmetric ligand was chosen in order to investigate if a small alteration of the coordiantion environment (pyridine versus carboxylate donor) could steer the metal ions in the heterobimetallic complex into a specific pocket of the ligand or not. The complexes have been characterized and investigated with mass spectrometry, electrochemistry, IR, UV-vis, EPR and Mössbauer spectroscopy. From CV and Mössbauer spectroscopy of the heterobimetallic complex it is proposed that the asymmetry is not able to steer the metals into different pockets and instead a mixture of two different isomers is created in the synthesis.
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