Magnetic phase transitions in nanoclusters of iron oxyhydroxides in polymeric matrices

Magnetic transitions in nanoclusters of iron oxyhydroxide in polymeric (sul focationite) and biopolymeric (ferritin) matrices are studied in the 4.2-50 K range by gamma-resonance (Mossbauer) spectroscopy. The hydration effect on the magnetic phase transitions. Hydration and swelling of the sulfocatio nite ion-exchange resin lower the magnetic transition temperature in cluste rs by Delta T-c0 = 3-4 K. This effect is considered using the thermodynamic model of magnetic phase transitions in nanoclusters and explained by the e xcess pressure of about 10(9) Pa arising due to freezing of the system and water transformation into ice with a volume increase. The Delta T-c0 shift estimated within the thermodynamic model of magnetic phase transitions for nanoclusters of about 3 nm in diameter ranges between (0.1-1.0)Delta T-c0 ( Delta T-c0 is the temperature of magnetic cluster transition) which does no t contradict experimental data. A 70% ferrite hydration also reduces Delta T-c0 by three or four K, which is consistent with the thermodynamic estimat es.