The variation of the blocking temperature T(subscript B) with measuring frequency f(subscript m) and applied field H are reported for Ni nanoparticles (NPs) embedded in SiO(subscript 2) matrix with the nominal composition Ni/SiO(subscript 2) (15/85). Transmission electron microscopy (TEM) of the sol-gel prepared NPs yielded a log-normal distribution with diameter D=3.8(0.2)nm whereas x-ray diffraction data yielded d~3.3nm. The T(subscript B) vs f(subscript m) variation for f(subscript m)=0.1 to 1000 Hz fits the equation T(subscript B)=T(subscript a)/In(f(subscript 0)/f(subscript m)) with f(subscript 0)=2.6x10(superscript 5) A/m (3200Oe) and m = 2(3/2) for lower(higher) H. These results are compared with the prediction of the Neel-Brown model of magnetic relaxation in non-interacting NPs.
Citation: Journal of Applied Physics
Pub Type: Journals
electron microscopy, magnetism, nanoparticle, Neel relaxation, x-ray diffraction