Impact of bond-order loss on surface and nanosolid magnetism

Incorporating the recent bond-order-length-strength correlation mechanism [Sun CQ, Bai HL, Li S, Tay BK, Jiang EY, Acta Mater 2004;52:501] into the Ising convention and the Brillouin function has enabled the unusual magnetic behavior of a ferromagnetic nanosolid and a surface to be reproduced using Monte Carlo simulations. Examination of the size and temperature dependence of the saturation magnetization (MS) of a solid of various structures reveals that: (i) at low temperatures, the MS increases inversely with solid size due to the contribution from the localized charges that are trapped by the deepened potential well of the lower-coordinated atoms in the surface skins; (ii) at the ambient temperatures, the MS drops with solid size because of the bond-order loss that suppresses the Curie temperature of the specimen; (iii) the quantized features of the surface to volume ratio of the solid is responsible for the observed MS oscillations of smaller clusters at low temperatures.