cbe455 lecture14 magnetism2 handout
TRANSCRIPT
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8/18/2019 CBE455 Lecture14 Magnetism2 Handout
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Instructor : Doh Chang Lee ([email protected])
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Ferromagnetic Superparamagnetic
Random magnetizationdue to thermal energy
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The characteristic time, !, for a magnetized domain to flip is given by:
( where K u is the magnetocrystalline anisotropy,
V is the volume of the nanocrystal (4 nm in “diameter”),
T is the temperature,
k is Boltzmann’s constant (8.61×10-5 eV/K) ,
f 0 is a frequency factor (use 10-9 sec-1) )
what is the minimum magnetocrystalline anisotropy ( K u) that is needed
for a memory storage application at room temperature (kT = 26 meV)?
Assume that the flip time should be longer than 100 sec.
1
"
= f 0 exp #K uV
kT
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We want to have a small size magnetic bit. (small V)
Magnetic energy scales with V.
To keep the magnet reliably magnetic, we need to either lower T or increase KV.