Nanoparticle (NP) assisted magnetic hyperthermia (NMH) is a clinically proven method for cancer treatment. High-Z magnetic NPs could also be a perspective object for combining hyperthermia with tumor radiosensitization. However, this application of NPs is little studied, and it is unclear as to what particle compositions one can rely on. Therefore, the present work focuses on the search of materials that combine alternating magnetic field induced heating and high atomic number related dose enhancement abilities. A theoretical evaluation of 24 promising NP compositions was performed: the values of dose enhancement factor (DEF) were determined for kilovoltage x-ray spectra (30–300 kVp), as well as specific absorption rate (SAR) values were calculated for various combinations of elemental compositions and particle size distributions. For the alternating magnetic fields with amplitude 75–200Oe and frequency 100kHz, the maximum obtained SAR values ranged from 0.35 to 6000Wg−1, while DEF values for studied compounds ranged from 1.07 to 1.59. The increase in the monodispersity of NPs led to a higher SAR, confirming well-known experimental data. The four types of SAR dependences on external magnetic field amplitude and anisotropy constant were found for various particle sizes. The most predictable SAR behavior corresponds to larger NPs (∼70–100 nm). Thus, based on these calculations, the most promising for the combination of NMH with radiotherapy, from a physical point of view, are La0.75Sr0.25MnO3, Gd5Si4, SmCo5, and Fe50Rh50. The greatest dose enhancement is expected for superficial radiotherapy (in the voltage range up to ∼60 kVp).
The effect of ytterbium impurity on the magnetic and galvanomagnetic properties of new diluted magnetic semiconductors Pb 1-x Sn x Te : Yb was investigated. Impurity-related Curie-Weiss paramagnetism was revealed. The concentration of magnetic centers and the ytterbium impurity-band occupancy as a function of impurity content were determined. The results are discussed assuming the formation of a ytterbiuminduced level under the valence-band top and a variation of the magnetic centers concentration due to changing of the mutual arrangement of the valence band, impurity level and Fermi-level position.
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