Magnetic properties of transition metal fluorides $M{\mathrm{F}}_2$ $(M=\mathrm{Mn},$ Fe, Co, Ni) via high-energy photon diffraction

We present an overview of recent results from nonresonant magnetic diffraction experiments on the antiferromagnetic compounds ${\mathrm{MnF}}_2,$ ${\mathrm{FeF}}_2,$ ${\mathrm{CoF}}_2,$ and ${\mathrm{NiF}}_2$ using high-energy synchrotron radiation of photon energies above 100 keV. New results are presented on the determination of the spin and of the $L/S$ ratio for ${\mathrm{CoF}}_2$ and ${\mathrm{NiF}}_2.$ For ${\mathrm{CoF}}_2,$ the saturation value of the long-range-ordered pure spin $S_z$ component $S_z=1.11\mathrm{}\left(1\right)\mathrm{}$ is considerably lower than the value $S_z=3/2\mathrm{}$ for the free ${\mathrm{Co}}^{2+}$ ion. This is in contrast to our results for ${\mathrm{NiF}}_2,$ where the full spin of the free transition-metal ion was found, $S_z=0.98\mathrm{}\left(1\right).$ The temperature dependence of the magnetization in the critical region as well as in the low-temperature region is also presented. For all compounds, Ising behavior is found in the critical regime, whereas the crossover to the low-temperature spin-wave behavior varies. We attribute this to different anisotropies in this series of compounds.