MAGNETIC-PROPERTIES OF IRON-OXIDE NANOCLUSTERS WITHIN MICRODOMAINS OFBLOCK-COPOLYMERS

The magnetic properties of gamma-Fe2O3 nanoclusters grown within the m icrodomains of optically transparent block copolymer films were invest igated. SQUID magnetometry and Fe-57 Mossbauer spectroscopy were emplo yed with characteristic measurement times of 100 s and 10(-s) s, respe ctively. The observed magnetism of the ca. 5 nm diameter particles was dominated by quantum-size effects, collective magnetic excitations, a nd superparamagnetic relaxation processes associated with the sub-magn etic domain gamma-Fe2O3 nanoclusters. The combination of these two tec hniques allowed determination of the values of the magnetic anisotropy constant (K = 1.58 x 10(5) J/m(3)) and the pre-exponential factor (ta u(0) = 4.2 x 10(-12) s) which determine the magnetic behavior of the n anocomposites. At low temperatures, the nanocomposite films exhibited hysteresis with the saturated coercivity, H-c(0), equal to 530 Oe. (C) 1998 Elsevier Science B.V. All rights reserved.