Magnetic properties of self-organized L10 FePtAg nanoparticle arrays

The magnetic properties of chemically synthesized high anisotropy L1(0) [Fe49Pt51](88)Ag-12 nanoparticle arrays have been studied as a function of annealing temperature. Particles were prepared by the simultaneous polyol reduction of platinum acetylacetonate and silver acetate and the thermal decomposition of iron carbonyl, yielding monodispersed particles of diameter similar to 3.5 nm. Addition of Ag lowers the ordering temperature of self-assembled arrays by similar to 150degreesC. After annealing at T-a = 500degreesC for 30 min in an Ar/H-2 atmosphere, the coercivity was 13,800 Oe. TEM and delta-M measurements indicate weak particle aggregation up to T-a = 400degreesC, with evidence of sintering at higher temperatures. Large ratios of remanent to hysteresis coercivity indicate a large distribution in anisotropy energies. Anomalously large thermal stability constants, KV/k(B)T, and switching volumes were measured, even in samples with very little evidence of sintering. Zero field viscosity versus remanence curves show evidence of exchange interactions. (C) 2003 Elsevier B.V. All rights reserved.