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18 Cards in this Set
- Front
- Back
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spin orbit interaction energy equation |
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how does the spin orbit interaction energy change |
greater for core electrons (small r) and heavy atoms (big Zeff) |
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difference between spin orbit interaction and exchange interaction |
s.o is usually way ******* smaller But. exchange interaction is isotropic nd s.o is fixed to relative axes. this means that the s.o is what is responsible for pulling magnetisation into a fixed direction relative to crystal axes |
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uniaxial anisotropy? |
found in hexagonal crystals |
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magnetic self energy equation |
aka magnetostatic energy |
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how magnetostatic energy and exchange interactions compete |
magnetostatic energy acts over a long range, whereas exchange interactions act on nearest neighbiur atoms . leads to a compromise, and the material organises itself into DOMAINS |
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how is the magnetostatic energy reduced in a uniformly magnetised bar |
1/N if divided into N domains |
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special property of materils with cubic anisotropy? |
can form closure domains at right nagles to reduce external field to zero |
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why will the material form domain walls |
to minimise magnetic self energy, will aim to make as many domains as possible |
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why does there have to be a balance between reducing magnetic self energy and making domains? |
because making domain walls has a high exchange energy cost |
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how do materials combat domain wall exchange energy |
spread the cost of wall formation over many spins |
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anisotropy energy per unit area |
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emergy of wall per unit area equation |
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what is remanence |
the proportion of magnetisation a sample retains once irreversible domain wall motion has taken place |
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hysteresis magnetisation curve |
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how shape affects anisotropy |
magnetic self energy depends on which direction the sample is magnetised in. shape anisotropy often larger than magnetocrystalline anisotropy |
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why do single domain particles exist |
there is a minimum volume, under which domain wall is energetically unfavourable for the sample |
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estimate of critical size |
25nm. done by assuming any particle smalled than domain wall width is a single domain particle. |
