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Search for magnetic refrigerant materials

Search for magnetic refrigerant materials. - Lian Zhang. WZI group meeting May 28 th 2003, UvA. Outline. What & why is MR? Search for candidate materials Gd 5 (Si,Ge) 4 Fe 2 Mn(Si,Ge) La(Fe,Si) 13 MnFe(P,As) Conclusion. Fleet. FR de Boer, KHJ Buschow

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Search for magnetic refrigerant materials

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  1. Search for magnetic refrigerant materials - Lian Zhang WZI group meeting May 28th 2003, UvA

  2. Outline • What & why is MR? • Search for candidate materials • Gd5(Si,Ge)4 • Fe2Mn(Si,Ge) • La(Fe,Si)13 • MnFe(P,As) • Conclusion

  3. Fleet FR de Boer, KHJ Buschow E Brück, A de Visser, J Klaasse, YK Huang O Tegus AL Wolf

  4. Why magnetic refrigeration? • Conventional gas expansion cooling • Ozone depletion • Global warming • Green MR • Higher efficiency • Less noisy • More compact • Low temperature capability

  5. Ericsson Q Q Magnetic Refrigeration • Magnetic-materials change in temperature if subjected to magnetic-field change Magnetocaloric effect B=0 Carnot S B0 T

  6. S Refrigerant capacity Table-like T S1 Sm S2 Tad T1 T2 Integration from isothermal magnetization curves Directly measure or compute from specific heat measurements

  7. Composite material B1 > B2 M S B T T1 T2 T3 T4 : : Tn TC Field-induced or not, behaves differently.

  8. Gd5(Si,Ge)4 Hysteresis M T Magnetostructural transition Misleading message

  9. O. Tegus Physica B 319 (2002) M. Nazih Solid State Comunications 126 (2003)

  10. Fe2Mn(Si1-xGex) • Fe3Si: • TC > 800 K • Fe2MnSi: • TC ~ 250 K • Cubic D03 • Heusler-type • Fe3Ge: • D019(HT) • L12(LT)

  11. D03  D019 L. Zhang J. Alloys Comp. 352 (2003)

  12. TC- Ge content Lattice change with Ge content

  13. L. Zhang Physica B 328 (2003)

  14. Disappointed!

  15. La(Fe,Si)13 • The highest 3d metal concentration (1:13) in RT intermetallic compounds • Failed to be a good permanent magnet • Cubic: weak anisotropy Palstra 1983

  16. Hypothetical LaFe13 structure: Space group = Fm-3c Unit cell = 8 f.u. = 112 atoms = 8 La + 8 FeI + 96 FeII FeI@8b FeII@96i Al, Si La @8a Moze 1999

  17. Modification • Substitution of Fe by other transition metals • Mn: failed to get single phase LaFe10.92Mn0.65Si1.43 • Co: LaFe10.92Co0.65Si1.43 has a 2nd transition at TC=265K • Doping with interstitial atoms • B: -Fe emerges in small amount of doping (B=0.2) • N: difficulty in diffusion makes sample inhomogeneous and broadens the transition enormously • C: saturated at C=0.5, while TC=250K

  18. Field step 0.005T Field step 0.1T Field step 0.02T Be cautious with the height of S peak when it is a 1st order field-induced transition.

  19. For the field-induced 1st order transition, the field-up S-T show point rotation symmetry with the field-down S-T curve.

  20. MnFe(P,As)

  21. s (B/f.u.) T(K) TN s 400 4 TN TC 3 300 AF AF TN 2 200 F AF 1 100 Orth Hex Tetr MnFeP MnFeAs Beckman-Lundgren, 1991

  22. O. Tegus Physica B 319 (2002)

  23. Virgin effect

  24. c b a c b a

  25. X=0.4 X=0.2

  26. X=0.4 X=0.2 X=0.2

  27. Conclusion • Materials for MR are ready • Much room for improvement • Behaviors vary: rich ingredients • Theories are called • Accommodate engineering challenges

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