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Ortega, D. and Chen, S. J. and Suzuki, K. and Garitaonandia, J. S. (2012) Room temperature spontaneous magnetization in calcined trioctylphosphine-ZnO nanoparticles. Journal of Applied Physics, 111 (7). 07C314. ISSN 00218979

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Abstract

In this work, it is demonstrated that capping with trioctylphosphine oxide (TOPO) induces a ferromagnetic response in free-standing ZnO nanoparticles upon calcination without the necessity of metallic doping. Samples were synthesized by precipitation of zinc acetate solutions in a basic medium followed by capping with TOPO and heat treatment in static aerobic conditions. Nanoparticles show a wurtzite-type structure with an average size of 14 nm, and magnetization measurements evidence a spontaneous magnetic moment at room temperature for calcined nanoparticles, in contrast with the diamagnetic response observed in non-calcined TOPO-capped nanoparticles. Giving the absence of any magnetic impurity or metal dopant that could account for the total magnetization, it is proposed that the magnetism would be consistent with a charge transfer mechanism promoted by a phosphorous doping upon calcination of TOPO over the nanoparticles. This situation leads to a spontaneous magnetic moment by the local fulfillment of Stoner’s criterion for ferromagnetism at the nanoparticles surface.

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