For all the compositions the crystallite sizes range from 9.5 to 12.9 nm. The smallest crystallites are observed for the Ni HT samples aged at 65 and 80 °C: 9.5 and 9.7 nm respectively. Changing the aging temperature from 65 to 80 °C has little or no effect on the crystallite size, with the largest effect observed in the Fe HT sample: from 11.9 to 12.9 nm.