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Local electronic and magnetic properties of pure and Mn-containing magnetocaloric LaFe13−xSixcompounds inferred from Mössbauer spectroscopy and magnetometry

Makarov, Sergey I. ; Krautz, Maria ; Salamon, Soma ; Skokov, Konstantin ; Teixeira, Cristiano S. ; Gutfleisch, Oliver ; Wende, Heiko ; Keune, Werner (2015)
Local electronic and magnetic properties of pure and Mn-containing magnetocaloric LaFe13−xSixcompounds inferred from Mössbauer spectroscopy and magnetometry.
In: Journal of Physics D: Applied Physics, 48 (30)
doi: 10.1088/0022-3727/48/30/305006
Article, Bibliographie

Abstract

Manganese containing La–Fe–Si alloys are important magnetocaloric compounds, since Mn atoms prevent segregation of hydrogen in partially hydrogenated La–Fe–Mn–Si alloys when their Curie temperature is tuned to room temperature by hydrogen. The effect of Mn alloying on the Fe atomic magnetic moment μ Fe is still rather unexplored. Therefore, we investigated the (local) magnetic and electric hyperfine interactions in the strongly magnetocaloric compound LaFe11.3Mn0.3Si1.4 and, for comparison, LaFe11.6Si1.4 by 57Fe Mössbauer spectroscopy, and the global magnetic properties by vibrating sample magnetometry. The NaZn13 structure was confirmed by x-ray diffraction. Two non-equivalent Fe lattice sites are known to exist in this material: the (96i) sites (FeII) of low local symmetry, and the highly symmetrical (8b) sites (FeI). At room temperature in the paramagnetic state, the electric hyperfine parameters of Fe atoms on both sites were obtained. At low temperatures (4.8 K), the observed magnetically split nuclear Zeeman sextets with broad apparent lines were analyzed in terms of a distribution P(B hf) of hyperfine magnetic fields B hf. The average hyperfine field 〈B hf〉, originating predominantly from FeII sites, was found to be rather high (30.7(1) T at 4.8 K) for LaFe11.6Si1.4, and the approximate relation 〈B hf〉 = Aμ Fe is confirmed for FeII sites, with A = 14.2 T/μ B. 〈B hf〉 is significantly reduced (to 27.7(1) T at 4.8 K) for the Mn-containing sample LaFe11.3Mn0.3Si1.4, providing evidence for a reduction by 9.7% of the average Fe atomic moment μFe from ~2.16 μ B to a value of ~1.95 μ B by Mn substitution of Fe. Our Mössbauer results are in good agreement with magnetometry, which reveals a reduction of the saturation magnetization of M s = 163.1(1) Am2 kg−1 of LaFe11.6Si1.4 by 10.5% due to Mn substitution.

Item Type: Article
Erschienen: 2015
Creators: Makarov, Sergey I. ; Krautz, Maria ; Salamon, Soma ; Skokov, Konstantin ; Teixeira, Cristiano S. ; Gutfleisch, Oliver ; Wende, Heiko ; Keune, Werner
Type of entry: Bibliographie
Title: Local electronic and magnetic properties of pure and Mn-containing magnetocaloric LaFe13−xSixcompounds inferred from Mössbauer spectroscopy and magnetometry
Language: English
Date: 5 August 2015
Publisher: IOP Publishing
Journal or Publication Title: Journal of Physics D: Applied Physics
Volume of the journal: 48
Issue Number: 30
DOI: 10.1088/0022-3727/48/30/305006
Abstract:

Manganese containing La–Fe–Si alloys are important magnetocaloric compounds, since Mn atoms prevent segregation of hydrogen in partially hydrogenated La–Fe–Mn–Si alloys when their Curie temperature is tuned to room temperature by hydrogen. The effect of Mn alloying on the Fe atomic magnetic moment μ Fe is still rather unexplored. Therefore, we investigated the (local) magnetic and electric hyperfine interactions in the strongly magnetocaloric compound LaFe11.3Mn0.3Si1.4 and, for comparison, LaFe11.6Si1.4 by 57Fe Mössbauer spectroscopy, and the global magnetic properties by vibrating sample magnetometry. The NaZn13 structure was confirmed by x-ray diffraction. Two non-equivalent Fe lattice sites are known to exist in this material: the (96i) sites (FeII) of low local symmetry, and the highly symmetrical (8b) sites (FeI). At room temperature in the paramagnetic state, the electric hyperfine parameters of Fe atoms on both sites were obtained. At low temperatures (4.8 K), the observed magnetically split nuclear Zeeman sextets with broad apparent lines were analyzed in terms of a distribution P(B hf) of hyperfine magnetic fields B hf. The average hyperfine field 〈B hf〉, originating predominantly from FeII sites, was found to be rather high (30.7(1) T at 4.8 K) for LaFe11.6Si1.4, and the approximate relation 〈B hf〉 = Aμ Fe is confirmed for FeII sites, with A = 14.2 T/μ B. 〈B hf〉 is significantly reduced (to 27.7(1) T at 4.8 K) for the Mn-containing sample LaFe11.3Mn0.3Si1.4, providing evidence for a reduction by 9.7% of the average Fe atomic moment μFe from ~2.16 μ B to a value of ~1.95 μ B by Mn substitution of Fe. Our Mössbauer results are in good agreement with magnetometry, which reveals a reduction of the saturation magnetization of M s = 163.1(1) Am2 kg−1 of LaFe11.6Si1.4 by 10.5% due to Mn substitution.

Uncontrolled Keywords: Mossbauer spectroscopy, intermetallic compounds, Fe and its alloys, magnetocaloric effect, magnetic cooling, saturation moments, magnetic susceptibility
Divisions: 11 Department of Materials and Earth Sciences > Material Science > Functional Materials
11 Department of Materials and Earth Sciences > Material Science
11 Department of Materials and Earth Sciences
Date Deposited: 08 Jan 2016 10:11
Last Modified: 08 Jan 2016 10:11
PPN:
Funders: Funded by Deutsche Forschungsgemeinschaft under grant SPP 1599 and by Stiftung Mercator (MERCUR) .
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