I have the normalized volume magnetic susceptibility from VSM values. I want to have the magnetic susceptibility of a big cylinder of the same material. Is this parameter a constant? or Do I have to re-calculate the value that I already have to a bigger volume? Thanks in advance for your comments!
Мolume magnetic susceptibility is dimensionless quantity.
Dimensionless quantity is a quantity to which no physical dimension is applicable.
If you would to measure susceptibility swith VSM technique, you must make some corrections especially for demagnetising filed wihich depends on the shape and the size of the sample Heff =Happl-[N][M] (in the MKSA system) where [N] is the demagnetization tensor , Trace[N]=1,([N] could be reduced as a simple number 1/3 if you have a sphere ) . For a cylinder, you have an axis of symmetry, ....... .
Of course, for low fields : X =M/ Heff
Thus, the demagnetization field's correction is required!
Just to sum up Yuri's and Mohamed's responses: magnetic susceptibility is the quantity which related to a material, and is not related to volume or shape of the sample. However, the measurement of susceptibility is made on a real sample with certain shape and dimensions. The shape of the sample may distort the results of the measurement due to demagnetisation. Therefore, if you have susceptibility calculated from VSM measurements, demagnetisation is likely. Unless your sample is long and slim, you should make corrections for demagnetisation to the VSM results, because these results are quantitatively imperfect. After corrections, you will have the real susceptibility of the investigated material and this is what you wanted to have.
But, if you wish to build a bigger cylinder from this material, please be aware that your cylinder will also exhibit demagnetisation. This means it will quantitatively respond to the applied magnetic field (get magnetised) differently than a long and slim sample or toroidal sample. The latter two shapes of samples are not affected by demagnetisation, so only from them you can get the susceptibility directly, withour corrections. The demagnetisation factor (N) may be fairly well assessed for cylinders, just google up the formulae.
Hello Mayra Llamas !
Magnetic susceptibility is the degree to which a material can be magnetized in an external magnetic field. If the ratio between the induced magnetization and the inducing field is expressed per unit volume, volume susceptibility (k) is defined as
k = M/H,
where M is the volume magnetization induced in a material of susceptibility k by the applied external field H. Volume susceptibility is a dimensionless quantity. The value depends on the measurement system used:
k(SI) = 4Pi k(cgs) = 4Pi G Oe–1,
where G and Oe are abbreviations for Gauss and Orstedt, respectively. The SI system should be used.
Mass, or specific, susceptibility is defined as
X = k/r,
where r is the density of the material. The dimensions of mass susceptibility are therefore cubic meters per kilogram.
The commonly used MS is measured at very low fields, usually not exceeding 0.5 mT, which have no influence on the NRM. It is therefore referred to as low-field susceptibility (klf). For comparison, fields of ~50 mT are required to change orientation in magnetite domains. High-field susceptibilities are measured in fields of a few hundred millilteslas and require equipment that is not available in the shipboard laboratory.
In practice, volume susceptibility is generally measured with core logging devices, for which calibration factors must be established to account for the specific geometry and effects of core conveyors and core liners. In the case of discrete specimen measurements, the mass of the specimen can be determined more accurately than volume and specific susceptibility is directly obtained. If average grain density and moisture content of the specimen are known, the specimen measurements can be compared with core logging measurements. Susceptibility values can then be normalized to mass and volume corrected for porosity. This can make susceptibility data more useful for quantitative estimates in conjunction with other mineral phases, such as carbonate, which are always normalized to dry mass.
References:
https://ipfs.io/ipfs/QmXoypizjW3WknFiJnKLwHCnL72vedxjQkDDP1mXWo6uco/wiki/Magnetic_susceptibility.html
Article Magnetic Resonance Imaging Measurement of Volume Magnetic Su...
And here is a good demagnetization factor calculator: http://www.magpar.net/static/magpar/doc/html/demagcalc.html
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