Magnetism superparamagnetic behavior

Taking into account the non-spherical shape of granules leads to deviation of the Ap/p(H) dependence from the square law, which becomes logarithmic in high magnetic fields. This is similar to the superparamagnetic behavior of magnetization. The parametrical dependence Ap/p oc (H /T% 3)... 

All the samples measured showed characteristic superparamagnetic behavior with a blocking temperature TB. An independent method of determining the parameters of the particle size distribution g(D) is by means of the analysis of magnetic measurements under equilibrium conditions, i.e. at temperatures above the superparamagnetic blocking temperature Tb- For this purpose we performed magnetization measurements as a function of field M(H) at different temperatures [4,5]. 

Malaescu I, Marin CN (2000) Deviation from the superparamagnetic behavior of fine-particle systems. J Magnet Magnetic Mater 218 91-96... 

The mPS microspheres show a typical superparamagnetic behavior at room temperature. No remanence was observed when the magnetic field was removed. 

Iron nanoparticles prepared by pyrolysis of poly(ferrocenylsilanes) inside periodic mesoporous sihca displayed the absence of room-temperature hysteresis in the magnetization curves which shows their superparamagnetic behavior [55]. However, magnetic properties cannot always be easily interpreted. For example, for this material data analysis of magnetization curves resulted in the ambiguous conclusion that either particle size distribution is bimodal, or iron particles have an oxide layer which behaves as small superparamagnetic nanoparticles. So magnetic measurements should be combined with other techniques (probably, in this case, EXAFS may be useful) to allow more accurate evaluation of particle structure. 

---