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jeebs
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Say we had a material which contains nanoparticles with uniaxial magnetic anisotropy - single domain "Stoner-Wohlfarth" particles. If you know what I'm talking about then you might be familiar with "field-cooled" and "zero field-cooled" curves, where the material has its magnetization plotted as a function of temperature, as it is cooled down from high temperature. The cooling is done both in the absence and presence of a magnetic field.
a typical set of results would look like this:
http://www.rsc.org/ejga/DT/2008/b807603k-ga.gif
where the black line is for the cooling with the field applied, and the red line is when there is no field.
I understand what is going on with the field-cooled curve. That's straightforward enough - as the temperature drops, the individual magnetic moments associated with each particle go from a totally disordered state, cancelling each other out over the whole sample, to being aligned in a common direction (parallel to the field).
However, I cannot get my head around the zero-field cooled curve. It has a peak at a temperature known as the "blocking temperature" of the particle (which is dependent on the particles' size and composition), then drops to zero as the temperature falls to zero.
Can anyone explain why the ZFC curve takes the shape that it does?
Thanks.
a typical set of results would look like this:
http://www.rsc.org/ejga/DT/2008/b807603k-ga.gif
where the black line is for the cooling with the field applied, and the red line is when there is no field.
I understand what is going on with the field-cooled curve. That's straightforward enough - as the temperature drops, the individual magnetic moments associated with each particle go from a totally disordered state, cancelling each other out over the whole sample, to being aligned in a common direction (parallel to the field).
However, I cannot get my head around the zero-field cooled curve. It has a peak at a temperature known as the "blocking temperature" of the particle (which is dependent on the particles' size and composition), then drops to zero as the temperature falls to zero.
Can anyone explain why the ZFC curve takes the shape that it does?
Thanks.
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