Surface spin polarization induced ferromagnetic Ag nanoparticles

We report on the observation of ferromagnetic spin polarized moments in 4.5 nm Ag nanoparticles. Both ferromagnetic and diamagnetic responses to an applied magnetic field were detected. The spin polarized moments shown under non-linear thermoinduced magnetization appeared on the surface atoms, rather than on all the atoms in particles. The saturation magnetization departed substantially from the Bloch T-3/2-law, showing the existence of magnetic anisotropy. The Heisenberg ferromagnetic spin wave model for H-a-aligned moments was then employed to identify the magnetic anisotropic energy gap of similar to 0.12 meV. Our results may be understood by assuming the surface magnetism model, in which the surface atoms give rise to polarized moments while the core atoms produce diamagnetic responses. (C) 2015 Elsevier B.V. All rights reserved.