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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 2 Peter Grünberg Institut Forschungszentrum Jülich

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The MCE MCE of Gd, Gschneider, et al 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 S –MCE obtains T of the MCE phenomenon

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Application of the MCE B = 0 T=T 1

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Application of the MCE B > 0 T>T 1

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Application of the MCE B > 0 T=T 1

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Application of the MCE B = 0 T

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Fe(ab)0~1/41/4 Fe(c)1/32/3 0 Si~3/501/4 Hexagonal P6 3 /mcm a = b ~ 6.8 Å c ~ 4.7 Å Fe(ab) Fe(c) Si Unit cell of Mn 5-x Fe x Si 3 at room temperature

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Fe(ab)0~1/41/4 Fe(c)1/32/3 0 Si~3/501/4 Hexagonal P6 3 /mcm a = b ~ 6.8 Å c ~ 4.7 Å Fe(ab) Fe(c) Si low cost non-toxic Unit cell of Mn 5-x Fe x Si 3 at room temperature

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Fe(ab)0~1/41/4 Fe(c)1/32/3 0 Si~3/501/4 Hexagonal P6 3 /mcm a = b ~ 6.8 Å c ~ 4.7 Å Fe(ab) Fe(c) Si low cost non-toxic structure flexible/ accommo-date various chemical substitutions understanding how the MCE works

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Synthesis: Mn 5-x Fe x Si 3 (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

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MCE in Mn 5-x Fe x Si 3 Songlin et al. 2002Recently at ORNL (X=4) MCE of Gd 5 Ge 2 Si 2 (2T)~27 J/kg K E. Brück et al. 2007

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TOF instrument (ideal for atomic occupation / high Q) high resolution:Δd/d ~0.1% Neutron the rescue… 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 Schematic view of POWGEN d [Å] Intensity Diamond pattern collected on POWGEN

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unique precision X theor% Fe(c) 1% Fe(ab)x calcul Normalized Intensity Mn 5-x Fe x Si 3 (x= 0 to 4) Fe(ab ) Fe(c ) Si Normalized Intensity d [Å] 300 K x=2

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Mn 5-x Fe x Si 3 (x= 0 to 4) Candini et al Very similar results. 300 K Our data from SNS

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Magnetization Measurements best MCE candidate

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Magnetization Measurements

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Moments II c-axis for x=4 in the ferromagnetic phase LT structure of Mn 5-x Fe x Si 3 x=4 Fe(ab ) Fe(c ) Si 10K Normalized Intensity d [Å] 300K Normalized Intensity d [Å] P6 3 /mcm

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DFT Calculations using program TB-LMTO-ASA, R. Tank et al. => occupations of Mn vs. Fe => stability of the AF and F phases Name wyck x y z ___________________ M1 2i M2 2i M3 2i M4 2i M5 2i Si1 2i Si2 2i Si3 2i X=4 From group to sub-group P6 3 /mcmP-1 1Mn for 4Fe Model 1 Mn on Fe(c) Model 2 Mn on Fe(ab) Fe(ab ) Fe(c ) Si

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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 B small magnetization on Si ~0.1 B (indirect effect) Total Density of States

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Mn 5-x Fe x Si 3 x=0 Negative MCE occurs here

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Mn 5-x Fe x Si 3 x=0

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Normalized Intensity d [Å] 85 K AF2 structure orthorhombic

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Mn 5-x Fe x Si 3 x=0 Space GroupP2 1 /m a (3) Å b (2) Å c6.9046(1) Å β (2)° Normalized Intensity d [Å] 60 K AF1 structure monoclinic

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

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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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