| 1. |
- Alouhmy, M., et al.
(författare)
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Effects of carbon implantation on the low temperature magnetism behavior in amorphous Fe93Zr7 films
- 2022
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Ingår i: Materials Science & Engineering. - : Elsevier. - 0921-5107 .- 1873-4944. ; 279
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Tidskriftsartikel (refereegranskat)abstract
- We present a detailed investigation on the effects of C-implantation on low temperature magnetic behavior in Fe93Zr7 amorphous films using spin wave theory, law of approach to saturation, and Alben and Becker's theory. Significant increase in Curie temperature with a decrease in coercivity were observed upon C-implantation. Bloch's law was used to analyze the temperature dependence of magnetization, and several important param-eters were extracted such as the stiffness constant of the spin wave, and the exchange constant. The local random anisotropy constant decreases from 0.35 to 0.19 MJ/m(3) with increasing carbon concentration from 0 to 11%. The ferromagnetic correlation length for which the anisotropy directions are assumed to be arbitrarily oriented in-creases significantly with increasing carbon content. By the use of the theory of Alben and Becker, we also extracted the local anisotropy from coercivity, and reasonable agreement was found with random magnetic anisotropy approach.
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| 2. |
- El Hachmi, Abdelhadi, et al.
(författare)
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Temperature induced structural phase transition in Sr3-xCaxFe2TeO9 (0 <= x <= 1) probed by Raman and Mossbauer techniques
- 2017
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Ingår i: Journal of Molecular Structure. - : Elsevier BV. - 0022-2860 .- 1872-8014. ; 1141, s. 484-494
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Tidskriftsartikel (refereegranskat)abstract
- A series of perovskites Sr3-xCaxFe2TeO9 (0 <= x <= 1) have been prepared in polycrystalline form by solid-state reaction method in air. These materials have been studied by X-ray powder diffraction method (XRPD) and Raman spectroscopy. An analysis of the XRD patterns at room temperature has shown that these compounds crystallize in a tetragonal system, space group I4/m. The structure contains alternating (Fe/Te)(2a)O-6 and (Fe/Te)(2b)O-6 octahedra, tilted in anti-phase in the basal ab-plane. The study of Raman spectroscopy at various temperatures shows a transition from tetragonal to cubic phase: I4/m -> Fm (3) over bar m. This phase transition occurs at high-temperature. Analysis of Raman spectra recorded at several temperatures shows that this phase transition appears near similar to 375 degrees C for (x = 0), similar to 435 degrees C for (x = 0.5) and similar to 451 degrees C for (x = 1). A proportional and gradual increase of temperature phase transition is observed as function of the calcium amount.
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| 3. |
- El Hachmi, A., et al.
(författare)
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Structural and Mössbauer Studies of Sr(1.5)Ca(1.5)Fe(2.25)Mo(0.75)O(9-delta)and Sr(1.92)Ca(1.08)Fe(2.04)W(9-delta)Double Perovskites
- 2020
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Ingår i: Journal of Structural Chemistry. - : Pleiades Publishing Ltd. - 0022-4766 .- 1573-8779. ; 61:6, s. 861-872
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Tidskriftsartikel (refereegranskat)abstract
- Sr(1.50)Ca(1.50)Fe(2.25)Mo(0.75)O(9-delta)and Sr(1.92)Ca(1.08)Fe(1.04)W(0.96)O(9-delta)double perovskites are synthesized in the polycrystalline form by a solid-state reaction route in air and studied at room temperature using the of PXRD, Raman and Mossbauer spectroscopy techniques. The Rietveld refinement analysis reveals that both compounds adopt a tetragonal system with the space groupI4/m and lattice parametersa=b= 5.5176(1) A andc= 7.8065(2) A for Sr(1.50)Ca(1.50)Fe(2.25)Mo(0.75)O(9-delta)anda=b= 5.5453(1) A andc= 7.8388(1) A for Sr1.92Ca1.08Fe2.04W0.96O9-delta. Raman spectra are consistent with the group theoretical analysis predicted for tetragonal symmetryI4/m(point group C4h5).Fe-57 Mossbauer spectra recorded at room temperature show a paramagnetic behavior for Sr1.50Ca1.50Fe2.25Mo0.75O9-delta, and magnetic ordering for Sr1.92Ca1.08Fe2.04W0.96O9-delta. The isomer shift (delta) and quadrupole splitting (Delta) values are characteristic of high-spin Fe(3+)in a distorted octahedral coordination.
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| 4. |
- El Hachmi, A., et al.
(författare)
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Structural, Magnetic and Optical Properties Study of Tellurium-Based Perovskites : Sr3-xPbxFe2TeO9 (0 <= x <= 2.25)
- 2020
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Ingår i: JOURNAL OF INORGANIC AND ORGANOMETALLIC POLYMERS AND MATERIALS. - : Springer Science and Business Media LLC. - 1574-1443 .- 1574-1451. ; 30:6, s. 1990-2006
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Tidskriftsartikel (refereegranskat)abstract
- Polycrystalline samples of the series of triple perovskites Sr3-xPbxFe2TeO9 (0 <= x <= 2.25) (SPFTO) were synthesized using solid state reaction. These materials have been studied by a combination of X-ray powder diffraction (XRPD), Mossbauer spectrometry, Raman and UV-Vis spectroscopies. The crystal structures were resolved by the Rietveld refinement method, and revealed that this Sr3-xPbxFe2TeO9 (0 <= x <= 2.25) system shows one space group change from tetragonal I4/m (0 <= x <= 1) to another tetragonal form I4/mmm (1.25 <= x <= 1.88) and a second transition to hexagonal R3 over bar m (2.08 <= x <= 2.25). An anti-site disordering of Fe and Te on the B sites has been detected indicating the presence of a partial amount of Te at Fe positions and vice versa. The valence state of iron in the Fe site was determined to be Fe(III) by Mossbauer spectrometry, which also revealed two sites in a concordance with the XRPD measurements. Fe-57 Mossbauer spectra measurements show paramagnetic and magnetic ordering behaviors. The observed Raman spectra as a function of composition show obvious changes on the positions (wavenumbers), the FWHM and the intensities of the modes confirming the phase transformations observed by the XRPD results. These structural transitions led to a distinct change in the optical band gap energy, varying from 2.14 to 1.85 eV.
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