Localized demagnetizing field

They improved their method by using finer magnetic elements, and developed a representation for the local demagnetizing field (Fukunaga and Kanai 1998). They concluded that a magnet composed of 60% soft and 40% hard grains with a grain size around 20 nm should be the best nanocomposite microstructure for the Nd-Fe-B system. 

In other cases, the demagnetizing field has a local character. In principle, it should be calculated in each point within matter. However, this constitutes a formidable task and a uniform demagnetizing field is still assumed most generally, with the demagnetizing field being expressed as in Eq. 16 and N being evaluated by approximating the sample shape to that of an ellipsoid. 

Then the sample is removed from the field of the magnets. To preserve the proton polarization, the demagnetization process is carried out adiabatically dB/dt < 7h 1oc/ where 7h is the gyromagnetic ratio for protons, Bioc is the mean local dipole field at the sites of protons). The value of the permanent magnetic field inside the sample slowly decreases finally reaching the value oiB 2tivn/7h-The entropy of the Zeeman proton reservoir at this moment is determined by expression... 

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