Weiss theory of ferromagnetism

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Atre
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Weiss theory of ferromagnetism

Postby Atre » Sun Oct 25, 2009 10:32 am UTC

Okay,

Weiss theory can be used to predict the heat capacity relating to ordering of electron spin, it does alright but has 2 major flaws.

The first of these is that (after Curie temp) the heat capacity component should drop straight to zero, but IRL there is a decaying tail of magnetism. This is due to random fluctuating magnetism inducing local order

The second flaw is that there is a major spike in heat capacity at the Curie temp that is noticeably above the model's prediction - Why is this? I can perhaps envisage this as magnetic domains shrinking and multiplying to offer more microstates but I'm not 100% sure...

Help please?

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You, sir, name?
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Re: Weiss theory of ferromagnetism

Postby You, sir, name? » Sun Oct 25, 2009 8:21 pm UTC

Atre wrote:The first of these is that (after Curie temp) the heat capacity component should drop straight to zero, but IRL there is a decaying tail of magnetism. This is due to random fluctuating magnetism inducing local order


Can't it be explained by the paramagnetic properties of a ferromagnet above TC? I don't remember much at all from the magnetism part of solid state physics, so I'm not sure, but it's what springs to mind.
I edit my posts a lot and sometimes the words wrong order words appear in sentences get messed up.

Noetherlite
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Re: Weiss theory of ferromagnetism

Postby Noetherlite » Sun Oct 25, 2009 8:54 pm UTC

You, sir, name? wrote:
Atre wrote:The first of these is that (after Curie temp) the heat capacity component should drop straight to zero, but IRL there is a decaying tail of magnetism. This is due to random fluctuating magnetism inducing local order


Can't it be explained by the paramagnetic properties of a ferromagnet above TC? I don't remember much at all from the magnetism part of solid state physics, so I'm not sure, but it's what springs to mind.


From what I recall, instant Paramagnetism above Tc would lead to instant zero magnetic specific heat capacity. So Atre's explanation is a necessary extension to Weiss theory (weiss has W = kM, fuller theories are summat like W= kM + lM* where M* is the fluctuationish term - my memory is a bit woolly on the details).

I don't know an exact answer to the second point, the best theory for magnetism in solid state is a renormalisation group theory, so that will hold the answers you are looking for - but it is ridiculously hard to understand and I couldn't find any details for you on a quick tour of the internet


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