Critical behavior of epitaxial antiferromagnetic insulators: Interdigital capacitance measurement of magnetic specific heat ofFeF2thin films

We have adapted the method of fabricating interdigital capacitors in the development of a technique for the measurement of magnetic specific-heat ($C_m$) critical behavior of micron-thick epitaxial films of antiferromagnetic insulators. This interdigital capacitance technique (ICT) was first tested on very carefully polished, bulk ${\mathrm{FeF}}_2$ surfaces. It was then applied to a study of high-quality 3-μm epitaxial films of ${\mathrm{FeF}}_2$ on lattice matching (001)-oriented ${\mathrm{ZnF}}_2$ substrates. Under ideal preparatory conditions, the ICT results in both cases exhibit the divergent critical behavior of a d=3 Ising system; namely, $C_m$=$A^{\pm }$‖t${\Vert }^{\mathrm{-}\alpha }$ with α=0.10±0.01 and amplitude ratio $A^{+}$/$A^{\mathrm{-}}$=0.60±0.05. .AE