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28 Cards in this Set
- Front
- Back
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the probability that a magnetic energy is occupied is given by |
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what is the spacing between J levels |
μbB |
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what is the mean atomic moment associated with this state |
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mean magnetisation M |
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how to check whether the saturation magnetisation is as predicted |
have a highly dilute solution of metal salts, meaning the ions are isolated and non interacting. can measure magnetisation M at different temperatures T |
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low field approximation |
μbB << kT, can use taylor series expansion to get M |
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paramagnetic susceptibility in low field equation |
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effective magneton number p equation |
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what is curie's law |
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what is the agreement of experimental and predicted p values in RARE EARTH METALS |
very good!!! apart from two but we dont care about them. |
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what is the agreement between experimental and predicted p values in TRANSITION METLS |
TRASH! but theyre a lot better if we arbitrarily set L = 0, meaning orbital angular momentum in transitional metals is quenched |
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why do rare earth metals have good agreement |
because magnetism arises in 4f shells, which make the electrons in this shell essentially isolated particles as they are far away from the nucleus |
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why do transition metals have TRASH agreement |
magnetism arises in 3d shell, which are responsible for chemical bonding, so they interact strongly with their environment. this can be represented as a crystal field, which causes a quenching of orbital moments |
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how do we directly measure L and S |
technology is amazing now! we use a XMCD machine (Xray Magnetic Circular Dichromism) |
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why are nanoclusters useful |
have diameters of range 1-5nm, consist of 10s-1000s of atoms can see how magnetism builds up atom by atom |
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potential applications of nanoclusters |
biomedical stuff, ultra high density storage |
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why are atomic moments in a nanocluster special |
they are locked together to form a single 'giant' atomic moment |
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energy of moment μ in applied magnetic field equation |
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average moment equation |
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does superparamagnetism obey curie's law |
ye boi |
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what is magnetic anisotropy |
the dependence of magnetic energy of the system on the direction in which the magnetisation vector is pointing, leading to 'hard' or 'easy' magnetism/axes |
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what is magnetocrystalline anisotropy |
when the atomic spin orbit interaction produces a dependence of magnetic energy on magnetisation relative to crystal axes |
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other sources of magnetic anisotropy |
shape stress surface |
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value of anisotropy energy barrier between two minimum energy states |
KV (K is energy density) |
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how temperature affects anisotropy barrier |
T > 50k, magnetic moment is easily excited past the barrier T >> 50K, barrier is irrelevant, cluster is superparamagnetic T < 50K, kT is too small to excite magnetic moment over barrier, magnetic moment is BLOCKED and lies along easy axes |
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how to estimate blocking temperature |
abitrarily set τ |
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paramagnetism in free electron gas |
small effect compared to in ions atoms and nanoparticles appropriate for describing paramagnetism of conduction electrons in metals |
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pauli paramagnetic susceptibility equation |
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