Magnetization temperature dependence in iron nanoparticles

The temperature dependence of the saturation magnetization of iron nanoparticles protected from oxidation by a shell of either magnesium or magnesium fluoride is reported. For iron crystallite sizes ranging from 3 to 18 nm, Bloch’s law is found to hold, but with nonbulk parameters dependent on both size and interface. The Bloch exponent decreases from the bulk value with decreasing size while the Bloch constant increases from the bulk value orders of magnitude with decreasing size. These size dependencies are different for the Mg and ${\mathrm{MgF}}_2$ coated samples to imply important interfacial effects.