Elastic torsion effects in magnetic nanoparticle diblock-copolymer structures

• Published in: Journal of physics. Condensed matter Vol. 22; no. 34; p. 346008
• Main Authors: Schulz, L, Schirmacher, W, Omran, A, Shah, V R, Böni, P, Petry, W, Müller-Buschbaum, P
• Format: Journal Article
• Language: English
• Published: Bristol IOP Publishing 01.09.2010; Institute of Physics
• Subjects: Anisotropy; Biophysics - methods; Condensed matter; Condensed matter: electronic structure, electrical, magnetic, and optical properties; Constants; Diamagnetism, paramagnetism and superparamagnetism; Elastic anisotropy; Elasticity; Exact sciences and technology; Magnetic properties and materials; Magnetic properties of nanostructures; Magnetics; Materials Testing; Models, Statistical; Nanocomposites; Nanomaterials; Nanoparticles; Nanoparticles - chemistry; Nanostructure; Physics; Physics - methods; Polymers - chemistry; Temperature; Iron oxide; Magnetization; Isoprene derivative copolymer; Magnetic hysteresis; Superparamagnetism; Polystyrene; Nanoparticles; Magnetic particles; Quantity ratio; Stoner model; Anisotropy; Temperature effects; Coated particle; Saturation magnetization
• ISSN: 0953-8984; 1361-648X; 1361-648X
• DOI: 10.1088/0953-8984/22/34/346008

Magnetic properties of thin composite films, consisting of non-interacting polystyrene-coated γ-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-Wohlfarth-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.