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Experimental and theoretical Studies of the Magnetocaloric Effect (MCE) in the Mn 5-x Fe x Si 3 Series

Experimental and theoretical Studies of the Magnetocaloric Effect (MCE) in the Mn 5-x Fe x Si 3 Series. Michael Gottschlich 1. Olivier Gourdon 1 , Michael Ohl 1 , Jörg Perßon 2. 1 Jülich Centre for Neutron Science outstation at the SNS at ORNL

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Experimental and theoretical Studies of the Magnetocaloric Effect (MCE) in the Mn 5-x Fe x Si 3 Series

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  1. Experimental and theoretical Studies of the Magnetocaloric Effect (MCE) in the Mn5-xFexSi3 Series Michael Gottschlich1 Olivier Gourdon1, Michael Ohl1, Jörg Perßon2 1 Jülich Centre for Neutron Science outstation at the SNS at ORNL 2 Peter Grünberg Institut Forschungszentrum Jülich

  2. The MCE The MCE is related mostly to the magnetic entropy changes of magnetic materials under the influence of an applied field • Tc where the phenomenon occurs • DS –MCE obtains • DT of the MCE phenomenon MCE of Gd, Gschneider, et al. 2005

  3. Application of the MCE T=T1 B = 0

  4. Application of the MCE T>T1 B > 0

  5. Application of the MCE T=T1 B > 0

  6. Application of the MCE T<T1 B = 0

  7. Unit cell of Mn5-xFexSi3 at room temperature Hexagonal P63/mcm Si Fe(ab) Fe(c) a = b ~ 6.8 Å c ~ 4.7 Å

  8. Unit cell of Mn5-xFexSi3 at room temperature Hexagonal P63/mcm • low cost • non-toxic Si Fe(ab) Fe(c) a = b ~ 6.8 Å c ~ 4.7 Å

  9. Unit cell of Mn5-xFexSi3 at room temperature Hexagonal P63/mcm • low cost • non-toxic • structure flexible/ accommo-date various chemical substitutions • understanding how the MCE works Si Fe(ab) Fe(c) a = b ~ 6.8 Å c ~ 4.7 Å

  10. Synthesis: Mn5-xFexSi3 (x=0,1,2,3,4) • polycrystalline samples prepared by inductive crucible free melting • structures preliminary confirmed by x-ray diffraction • magnetization measurements • chemical Analysis

  11. MCE in Mn5-xFexSi3 MCE of Gd5Ge2Si2 (2T)~27 J/kg K E. Brück et al. 2007 Songlin et al. 2002 Recently at ORNL (X=4)

  12. Neutron the rescue… 80000 60000 40000 20000 0 Intensity 0 0.5 1.0 d [Å] • to elucidate the coloring problem: Fe vs. Mn on both sites (no discernable by X-ray) • to investigate the magnetic ordering …POWGEN at the SNS • TOF instrument (ideal for atomic occupation / high Q) • high resolution:Δd/d ~0.1% Diamond pattern collected on POWGEN Schematic view of POWGEN

  13. Mn5-xFexSi3 (x= 0 to 4) Si Fe(ab) Fe(c) 300 K 1.0 0.9 0.8 0.7 0.6 0.5 0.4 0.3 0.2 0.1 0.0 x=2 Normalized Intensity Normalized Intensity “unique precision” 0.5 1.0 1.5 2.0 2.5 3.0 3.5 d [Å]

  14. Mn5-xFexSi3 (x= 0 to 4) 300 K Candini et al. 2004 Our data from SNS Very similar results.

  15. Magnetization Measurements best MCE candidate

  16. Magnetization Measurements

  17. LT structure of Mn5-xFexSi3 x=4 1.0 0.9 0.8 0.7 0.6 0.5 0.4 0.3 0.2 0.1 0.0 Normalized Intensity 300K 0.5 1.0 1.5 2.0 2.5 3.0 3.5 d [Å] 1.0 0.9 0.8 0.7 0.6 0.5 0.4 0.3 0.2 0.1 0.0 Normalized Intensity 10K 0.5 1.0 1.5 2.0 2.5 3.0 3.5 d [Å] P63/mc‘m‘ Si Fe(ab) Fe(c) Moments II c-axis for x=4 in the ferromagnetic phase

  18. DFT Calculations using program „TB-LMTO-ASA“, R. Tank et al. => occupations of Mn vs. Fe => stability of the AF and F phases From group to sub-group X=4 Si 1Mn for 4Fe Name wyck x y z ___________________ M1 2i 0.3333 0.6667 0.0000 M2 2i 0.6667 0.3333 0.5000 M3 2i 0.7636 0.7636 0.2500 M4 2i 0.2364 0.0000 0.2500 M5 2i 0.0000 0.2364 0.2500 Si1 2i 0.4043 0.4043 0.2500 Si2 2i 0.5957 0.0000 0.2500 Si3 2i 0.0000 0.5957 0.2500 Fe(ab) Fe(c) P63/mcm P-1 Model 1 Mn on Fe(c) Model 2 Mn on Fe(ab)

  19. DFT Calculations LDA and LSDA calculations have been performed both confirmed that: Model 1 Mn on Fe(c) Model 2 Mn on Fe(ab) is less stable than by 0.5 eV/unit cell in agreement with the refined data • magnetic moments of ~1.7 mB • small magnetization on Si ~0.1 mB (indirect effect) Total Density of States

  20. Mn5-xFexSi3 x=0 Negative MCE occurs here

  21. Mn5-xFexSi3 x=0

  22. Mn5-xFexSi3 x=0 AF2 structure orthorhombic 1.0 0.9 0.8 0.7 0.6 0.5 0.4 0.3 0.2 0.1 0.0 85 K Normalized Intensity 0.5 1.0 1.5 2.0 2.5 3.0 3.5 d [Å]

  23. Mn5-xFexSi3 x=0 AF1 structure monoclinic 60 K Normalized Intensity d [Å]

  24. Acknowledgements POWGEN at SNS ORNL • Jason Hodges • Ashfia Huq • HB2a at HFIR ORNL • Ovidiu Garlea • Clarina Dela Cruz • JANA Software • Vaclav Petricek

  25. Summary and future direction • the combination of experimental data and theoretical tools lead to a better understanding of the MCE property. • chemical substitutions • single crystals for further neutron scattering experiments Thank you very much for your attention!

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