1 / 15

Outline

Neutron Scattering Analysis of Magnetostructural Phase Transformations of High Magnetic Field Textured Shape Memory Alloys. Ben Shassere, Orlando Rios, Khorgolkhuu Odbadrakh, Jason Hodges, Gerry Ludtka, Don Nicholson, Boyd Evans Oak Ridge National Laborator y. Outline.

jennis
Download Presentation

Outline

An Image/Link below is provided (as is) to download presentation Download Policy: Content on the Website is provided to you AS IS for your information and personal use and may not be sold / licensed / shared on other websites without getting consent from its author. Content is provided to you AS IS for your information and personal use only. Download presentation by click this link. While downloading, if for some reason you are not able to download a presentation, the publisher may have deleted the file from their server. During download, if you can't get a presentation, the file might be deleted by the publisher.

E N D

Presentation Transcript

  1. Neutron Scattering Analysis of Magnetostructural Phase Transformations of High Magnetic Field Textured Shape Memory Alloys Ben Shassere, Orlando Rios, Khorgolkhuu Odbadrakh, Jason Hodges, Gerry Ludtka, Don Nicholson, Boyd Evans Oak Ridge National Laboratory

  2. Outline • Introduction to magnetic cooling • Why magnetic cooling • Thermodynamics of the magnetocaloric effect (MCE) • First principles modeling of MCE in Ni/Mn/Ga alloys • Reasons for choosing this material • Sample preparation and DSC heating curves • Neutron diffraction results • Conclusion for Ni/Mn/Ga alloys • Iron based shape memory alloys

  3. Magnetic cooling • Magnetocaloric effect is an intrinsic property of all magnetic solids • Occurs near Curie point in Ferromagnetic materials • Magnetic moments align (unpaired 3d or 4f electrons) when placed in magnetic field • Magnetic entropy is lowered on exposure to field • May be enhanced by combined magnetic/structural transformations • MCE commonly used to reach temperatures near absolute zero (micro-Kelvin) † † White, Experimental Techniques in Low-Temperature Physics, Oxford Press 2002

  4. Why Magnetic Cooling • Energy Efficient – Magnetization is 99%+ efficient – Conventional refrigeration systems already operate near theoretical efficiency limit of ~30% – Magnetic refrigeration theoretical efficiency of 60% – Reduces use of fossil fuels – HVACR accounts for 32% of US building energy consumption – Refrigeration accounts for 15% of worldwide energy use • Environmentally Friendly – No CFC’s (ozone depletion) – No HFC’s (greenhouse emissions) – Less CO2 (greenhouse emissions) – Solid refrigerant – Safe heat transfer fluids (water, antifreeze, air) – Simple, low pressure mechanical system

  5. Magneto-Caloric Effect (MCE) Basic Thermodynamics MCE Pecharsky and Gschneidner P.R.L. 1997 Magnetic contribution to Entropy change • Coupling between Structural and Magnetic Phase Transitions results in Giant MCE • Combining Modeling with Experimental Investigation to search for suitable composition and temperature range

  6. Reasons for Choosing Ni/Mn/Ga • Coupling of magnetic and structural transitions causing giant magnetocaloric effect around Curie temperature • Utilization of non rare earth materials • Utilization of dopants allows for modification of the Curie temperature

  7. First principles modeling of MCE in Ni2MnGa Ground State: Density Functional Theory determination using LSMS Finite Temperature: Combining First Principles with Statistical Mechanics: Wang-Landau LSMS • Magnetic Moment Relaxation within LSDA approximation. • Ga stabilizes Ni-Mn in FM phase. • Only Mn-Ni nearest neighbor spin interaction dominates. • Large Mn and small Ni moments (3.5μB,0.3μB). • WL DOS based on DFT energy for non-collinear magnetic states. • 144 atoms and 1500 walkers: 216,000 processors. • PM States have larger moments: Magnetic field can more easily effect a large number of states. • Large MCE: ΔE of Ni(0.3μB) flip same as Mn(3.5μB) flip.

  8. Bulk Ni/Mn/Ga Sample Preparation Bulk Samples • Ni/Mn/Ga (2.2/0.8/1 at %) • Ni/Mn/Ga (2.26/0.77/0.97 at %) • Ni/Mn/Ga (2.23/0.77/1 at %) • Ni/Mn/Ga/Fe/Cu (2.3/0.74/0.96/0.03/0.03 at %) • Ni/Mn/Ga/Fe/Cu (2.34/0.71/0.95/0.06/0.06 at %) Preparation • Arc melted rod of material • Remelted sample 4 times • Annealed at ºC

  9. Specific Heat Capacity of NiMnGa Alloys from DSC Heating Curves • Delete text box and insert picture here • Ni/Mn/Ga/Fe/Cu (2.3/0.74/0.96/0.03/0.03) 5 Ni/Mn/Ga (2.2/0.8/1 at %) 6 Ni/Mn/Ga (2.26/0.77/0.97 at %) 7 Ni/Mn/Ga (2.23/0.77/1 at %) • Ni/Mn/Ga/Fe/Cu (2/34/0.71/0.95/0.06/0.06) Coupled Magnetic and Structural Transitions • Magnetic and structural transition temperatures • Modified Curie temperatures Magnetic Transitions Structural Transitions

  10. Neutron Scattering Results for Ni/Mn/Ga/Fe/Cu (2.3/0.74/0.96/0.03/0.03 at %) Transition between 190 C and 210 C Transition between 110 C and 130 C Temperature in ºC 210 190 170 150 130 110 90 70 50 30

  11. Conclusions for Ni/Mn/Ga Alloys • Neutron scattering shows phase transitional temperatures • Ni/Mn/Ga shows magnetocaloric effect around Curie temperature • Structural and magnetic transitions can be modified using Cu and Fe doping elements • First principles modeling allows for greater understanding of the ground state properties and contributes to understanding the thermodynamics involved

  12. Iron Based High Magnetic Field Textured Shape Memory Alloys Preparation • Arc melted button • Remelted 4 times • Drop cast into ¾” Cylinder • Sectioned into 3 in bars • Melted and Textured at 1420 C at 20 T

  13. Resistivity Characterization Under High Magnetic Field Shifting phase transition between 6T and 12T

  14. Acknowledgements This research is sponsored by the Laboratory Directed Research and Development Program (ORNL), the Center for Defect Physics in Structural Materials (CDP), an Energy Frontier Research Center funded by the U.S. Department of Energy, Office of Science, Office of Basic Energy Sciences and by the Division of Materials Sciences and Engineering,  Office of Basic Energy Sciences (US DOE)

More Related