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Magnetic Shape Memory Alloys
Chris Ziegler
ENMA490
September 10, 2002
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Shape Memory Alloys
-General Description of how they work
-Twinning
Combinatorial Approach
-Cantilever Fabrication
-Deposition
-Rapid Analysis
Magnetic Shape Memory Alloys
-Similar functionality to SMA
-Magnetostriction
-Applications and downfalls
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Shape Memory Alloys
-Austenite-Martensite Transformation
Austenite
Cooling
Polydomain Martensite
Applied Stress
Single-domain Martensite
Re-heating
Austenite
-Twinning- Formation of symmetrical, inter-grown crystals
-Shape Memory Alloys (NiTi, NiMnGa) are used in switches, actuators, airplane components, and
other applications.
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The Combinatorial Approach to finding new Shape Memory Alloys
Capacitance Measurement
-Change in capacitance as a function of cantilever deflection
-1 Composition at a time!
Optical Measurement
-Cantilever Library Fabricated
-Sputter Deposition of composition spread
-Optical Measurement
-Shape Memory Effect seen by eye
Combinatorial Science = Rapid Characterization of a spread of material
V
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Composition Spread
xx
guns
spread profile
distance between guns & substrate
Raising and lowering the stage in which the sample rests results in different composition gradients across wafer surface.
Picture of the 3 sputtering guns, each capable of holding a
different “target”
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Rapid Detection of Martensitic Transformation
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Magnetic Shape Memory Alloys: What are they?
-An alloy that demonstrates the Austenite to Martensite phase transformation (Shape Memory Effect)
-An alloy that is ferromagnetic (possibly a need for Iron, Cobalt, or Nickel in the alloy)
-The most well known “MSMA” is NiMnGa
-Nickel Manganese Gallium has an L21 crystal structure
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How do they work?
Magnetic Moments without applied magnetic Field
Parallel Alignment of Magnetic
Moments within the twins with applied
field
Redistribution of twin “variants”
http://www.fyslab.hut.fi/epm/heusler/
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Magnetostriction
Definition: Spontaneous deformation of a solid in response to its magnetization (James and Wuttig)
-Discovered in 1842 by James Joule while experimenting with nickel (a ferromagnetic material)
-examples: Terfenol-D, Alloys including Iron, Cobalt, or Nickel, PZT, etc…
-If martensitic material is ferromagnetic there is a possibility that application of a magnetic field will rearrange the martensite variants! This results in strains one order of magnitude or higher than that of Giant Magnetostrictive materials.
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Thin Film Applications for Magnetic Shape Memory Alloys
-Switches and Actuators that are both more responsive and more cost-efficient.
-Microwrapper – used for controlling micro-organisms and even tumor removal in the medical industry
-Metal MSMA more responsive and less brittle than Terfenol-D
-Associated Large-Energy Density for MEMS use
http://www.afrlhorizons.com/Briefs/Sept02/OSR0203.html
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Summary
-MSMA’s exist due to their ferromagnetic and phase transformation characteristics
-Metal Alloys such as NiMnGa exhibit strains on the order of 6% as compared to the .2% exhibited by Terfenol-D
-Actuation by application of a magnetic field is inexpensive, very sensitive, and requires less time than the heating required for general SMA’s
-Very few MSMA’s well known at this point paving the way for Combinatorial Discovery
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QUESTIONS?
Football is good!