How much should the magnetic field in DC and AC magnetic measurements be? Should the magnetic field be as low as possible? The AC magnetization is always performed in a low field(1~3 Oe). Can anyone explain this?
The answer depends not only of you want to measure (such as the magnetic ground state or the magnetic properties as susceptibility), but also of what kind of material you have (soft or hard ferromagnetic, paramagnetic o diamagnetic, diluted magnetic material) and also on what kind of equipment you have to perform the measurments: (a VSM, a SQUID or whatever)
@Sergio Ferrari: Dear Dr Sergio Ferrari, thanks for you reply. Would you like to provide some detailed information or references about this topic?
Ok, @Chenyang Zhang, I will try to give you detailed information about this topic. First thing you neeed to consider when applying a field to make a DC or AC magnetic measurement is what kind of sample you have. Depending of the material of your sample the magnetic behaviour can be predicted to be ferromagnetic (spontaneus aligment of magnetic moments of atoms), paramagnetic (atoms have magnetic moments but they are at random directions, they only align under an applied magnetic field) or diamagnetic (the atoms will aligned oppositivily to the applied magnetic field). Also ferromagnetism can be divided into hard ferrromagnets (as NdFeB magnets) or weak ferromagnets (as iron, iron alloys, etc).
For example a weak ferromagnet can saturate with a small applied field, so depending of you want to measure the saturation magnetization or/and the magnetic hysterisis cycle you should set the applied magnetic field differently.
I can continue what I recommend that you read some book about magnetism or ask someone of your University that has made magnetic measurments before.
The AC magnetic characterization is generally performed at relatively low fields because of obvious constraints related to the exciting power and power dissipated in the material. On the other hand, the interest for AC behavior is generally restricted to soft magnets.
You might have a look at the book "Measurement and characterization of magnetic materials", Elsevier-Academic Press (author F. Fiorillo)
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