title: Elastic torsion effects in magnetic nanoparticle diblock-copolymer structures.
abstract: 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.
authors.affiliation: Physik-Department E13, Technische Universität München, Garching, Germany.
authors.forename: L
authors.initials: L
authors.lastname: Schulz
authors.forename: W
authors.initials: W
authors.lastname: Schirmacher
authors.forename: A
authors.initials: A
authors.lastname: Omran
authors.forename: V R
authors.initials: VR
authors.lastname: Shah
authors.forename: P
authors.initials: P
authors.lastname: Böni
authors.forename: W
authors.initials: W
authors.lastname: Petry
authors.forename: P
authors.initials: P
authors.lastname: Müller-Buschbaum
mesh_terms: D016880:Anisotropy; D001703:Biophysics / Q000379:methods; D004548:Elasticity; D008280:Magnetics; D008422:Materials Testing; D015233:Models, Statistical; D053758:Nanoparticles / Q000737:chemistry*; D010825:Physics / Q000379:methods; D011108:Polymers / Q000737:chemistry*; D013696:Temperature
chemical_list: D011108:Polymers