Magnetic Characterization Techniques for Nanomaterials by Challa S.S.R. Kumar

Author:Challa S.S.R. Kumar
Language: eng
Format: epub
Publisher: Springer Berlin Heidelberg, Berlin, Heidelberg

5.3.2 Location of the FM/SMP Transition

As concluded in Sect. 5.2, MNPs with sizes next to the SPM/FM limit are the most suitable for low-H 0 applications. This optimum MNP volume (Eq. 8.13) depends on f and K and takes place at a given T B . Then, for a fixed frequency, χ″ (T) measurements may be used to determine T B , since at this temperature χ″ presents a peak (Eq. 8.11). The location of T B helps to conclude whether smaller (if T B  > 36 °C) or larger (if T B  < 36 °C) MNPs will optimize SAR for hyperthermia applications, thus serving as feedback for the synthesis of optimized MNPs. In the low-field range where the LRT applies (Eq. 8.3), SAR is linearly proportional to χ″ (Eq. 8.2) and χ″(T) provides equivalent information than SAR(T).

Figure 8.7b shows the good agreement between χ″(T) and SAR(T) measurements on a system of iron oxide nanoparticles. χ″(T) was determined using the MPMS and PPMS devices from Quantum Design Inc., and SAR(T) was obtained by the pulse heating method in adiabatic conditions [139]. The clear advantage of calorimetric SAR(T) measurements is that the AMF parameters used are typical of magnetic hyperthermia.

Eventually, when the H 0 values overcome the limits of the LRT, and the relationship between χ″ and SAR is unclear, it becomes evident that the direct determination of SAR(T) will provide more reliable information than χ″ about the temperature at which the dissipation peak takes place.

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