Elastic Torsion Effects in Magnetic Nanoparticle Diblock-Copolymer Structures

Magnetic properties of thin composite films, consisting of non-interacting polystyrene-coated $\gamma$ - Fe 2 O 3 (maghemite) nanoparticles embedded into polystyrene-block-polyisoprene P(S- b -I) diblock-copolymer films are investigated. Different particle concentrations, ranging from 0.7 to 43 wt%, have been used. The magnetization measured as a function of external field and temperature shows typical features of anisotropic superparamagnets including a hysteresis at low temperatures and blocking phenomena. However, the data cannot be reconciled with the unmodified Stoner\textendash{}Wohlfarth\textendash{}Néel theory. Applying an appropriate generalization we find evidence for either an elastic torque being exerted on the nanoparticles by the field or a broad distribution of anisotropy constants.     «

Magnetic properties of thin composite films, consisting of non-interacting polystyrene-coated $\gamma$ - Fe 2 O 3 (maghemite) nanoparticles embedded into polystyrene-block-polyisoprene P(S- b -I) diblock-copolymer films are investigated. Different particle concentrations, ranging from 0.7 to 43 wt%, have been used. The magnetization measured as a function of external field and temperature shows typical features of anisotropic superparamagnets including a hysteresis at low temperatures and blocki...     »