Large magnetocaloric effect, moment, and coercivity enhancement after coating Ni nanoparticles with Ag

Abstract

We observe a large magnetocaloric effect in monodisperse Ni and Ni coreAgshell nanoparticles in the superparamagnetic region. The organically passivated Ni nanospheres show a large magnetic entropy change of 0.9 J-kg-1-K for a 3 T magnetic field change. In comparison to the surfactant-coated Ni nanoparticles, the NicoreAgshell nanoparticles show an enhanced coercivity, magnetization, and magnetocaloric effect (1.3 kg-K for a 3 T magnetic field change). The coercivity at 10 K increases from 360 Oe for Ni nanoparticles to nearly 610 Oe for Ni coreAgshell particles. This large enhancement is attributed to the enhanced inter-particle interaction, which is mediated by the metallic shell, over the relatively weaker dipolar interaction in the surfactant-coated Ni nanoparticles, and to modification of the surface spin structure. What a difference a coat makes: A large magnetocaloric effect is observed in monodisperse Ni and NicoreAgshell nanoparticles in the superparamagnetic region. The organically passivated Ni nanospheres show a large magnetic entropy change of 0.9 J-kg-1-K for a 3 T magnetic field change. This large enhancement is attributed to the enhanced inter-particle interaction mediated by the metallic shell, and modification of the surface spin structure. © 2014 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.