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umby
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Hi, I am looking for the temperature dependence of the saturation magnetization of Fe. Any help?
many thanks!Charles Link said:Here is a previous thread on Physics Forums about the temperature dependence of the magnetization and the Curie temperature. The formula of interest is contained in posts 2 and 3: https://www.physicsforums.com/threa...perature-relationship-in-ferromagnets.923380/ The saturation magnetization is approximately the same as the magnetization of a permanent magnet, but they are not exactly the same thing. ## \\ ## If the material does not make a permanent magnet, I think the same formula may still be applicable to give the approximate magnetization that occurs for relatively high applied magnetic fields.
I agree, and this is why I told the OP that saturation and the level of magnetization ## M ## in a permanent magnet are not exactly the same thing.essenmein said:Isn't saturation defined as all magnetic dipoles aligned? Ie a further increase of external magnetic field does not increase the magnetic flux beyond that of vacuum. Short of the change in density due to temperature the number of dipoles doesn't significantly change, therefore Bsat should be ~ temp independent?
Now its willingness to hold onto that magnetization does depend on temp.
Approaching the Curie temperature, the saturation magnetization (the magnetic moment per unit volume at saturation) of a ferromagnetic material should not go to zero?essenmein said:Isn't saturation defined as all magnetic dipoles aligned? Ie a further increase of external magnetic field does not increase the magnetic flux beyond that of vacuum. Short of the change in density due to temperature the number of dipoles doesn't significantly change, therefore Bsat should be ~ temp independent?
Now its willingness to hold onto that magnetization does depend on temp.
essenmein said:Have to be careful with terminology here.
Saturation = all magnetic dipoles aligned, this is a physical property based on the number of atoms in the material that have a magnetic moment. This changes only with density (with in the constraints of classical physics at least, I assume you could change this property with extremes of gravity or radiation).
Saturation B max does not change with temperature, however the external applied field needed to reach this does (magnetic susceptibility).
Now basically all magnetic materials have some level of hysteresis, ie apply an external field, and remove it, and some level of internal magnetization remains if the forces due to the now aligned dipoles is not enough to disorder them again. All magnets will self demagnetize to some extent based on this, if you go look lat the load lines of neo materials, this is very shape dependent (and temperature dependent). The field the moments induce wants to undo those aligned moments, and if the shape (and external reluctance) is such that the induced field is enough to demag, they will demag to that point.
The currie temperature is where thermal agitation is overcoming the "stickiness" of those magnetic moments within the material, and they spontaneous fall back into disorder (currie point). Ie the material will no longer hold a magnetic field once an external field is removed.
This thermal agitation also affects how the dipoles want to align to an external field, ie they are vibrating now and take more force to hold in place, the hotter a material gets the more the thermal "vibrations" over power the aligning forces of the external field on the magnetic dipole. So while its harder to align the individual atoms, they can still be aligned with enough field.
So as I understand it Bmax does not change, but susceptibility does, ie permeability is temp dependent.
The curve does not show the tremendously dramatic change that occurs at the Curie temperature (below the Curie temperature, the susceptibility is much higher), but otherwise, I think it has the right idea. Also, be sure and see my post 8 including a couple additions to it.umby said:Can i try to summarize with a picture?
View attachment 227431
So, the saturation is always the same, but the higher the temperature is, the higher the field needed to reach it; then, at a given external field, the same material can be at saturation at a certain temperature but can be not at saturation at an higher temperature.
umby said:Can i try to summarize with a picture?
View attachment 227431
So, the saturation is always the same, but the higher the temperature is, the higher the field needed to reach it; then, at a given external field, the same material can be at saturation at a certain temperature but can be not at saturation at an higher temperature.
essenmein said:Yup, so the slope of T1, T2 etc is the permeability of the material, if you plotted this value over a wide range of temp above and below the currie temp, it would be high below the currie temp, and nose dive to barely above u0, which is the dramatic effect Charles Link is referring too.
essenmein said:The field the moments induce wants to undo those aligned moments, and if the shape (and external reluctance) is such that the induced field is enough to demag, they will demag to that point.
Saturation magnetization is the maximum magnetic moment per unit volume that a material can have when all of its magnetic domains are aligned in the same direction.
As temperature increases, the saturation magnetization of iron decreases. This is because thermal energy disrupts the alignment of magnetic domains, resulting in a decrease in overall magnetic moment.
The Curie temperature of iron is 1043 K (770°C). Above this temperature, iron loses its ferromagnetic properties and becomes paramagnetic.
The saturation magnetization of iron can be measured using a magnetometer, which applies a magnetic field to the material and measures the resulting magnetic moment. The saturation magnetization is reached when the magnetic moment reaches a plateau.
The saturation magnetization of iron can be affected by impurities and defects in the material, as well as by external factors like mechanical stress and magnetic fields. The crystal structure and composition of the iron can also impact its saturation magnetization.