Comparison of the Critical Single-Domain Size for Fe3O4 and γ-Fe2O3

On theoretical grounds the critical single-domain size for $\mathrm{\gamma -}{\mathrm{Fe}}_2{\mathrm{O}}_3$ is expected to be somewhat larger than for ${\mathrm{Fe}}_3{\mathrm{O}}_4$ . Measurements of the variation of coercive force with temperature and with compression for a single iron-oxide powder in both the ${\mathrm{Fe}}_3{\mathrm{O}}_4$ and $\mathrm{\gamma -}{\mathrm{Fe}}_2{\mathrm{O}}_3$ forms yield strong evidence in support of this conclusion.