Growth and Characterization of the Multiferroic Barium Transition Metal Fluorides Ba$M$F$_{4}$

We have investigated the temperature dependent growth, as well as the magnetic and ferroelectric properties of thin films of the isostructural compounds Ba$M$F$_{4}$, where $M=$Fe, Co, Ni. The films were grown by molecular beam epitaxy to thicknesses of 50 or 100 nm on single crystal Al$_{2}$O$_{3}$ (0001) substrates. X-ray diffraction shows that this family of films grow epitaxially in the (010) orientation, but are twinned in the plane, with three domain orientations rotated by 120$^{\circ}$ relative to one another. Measurements of the remanent hysteresis via interdigitated electrodes show that the compounds $M=$Co, and Ni are ferroelectric, but no switching behavior was observed in the Fe system at electric fields up to 400 kV/cm. Measurements of the field-cooled and zero-field-cooled magnetic moment confirm the existence of low temperature magnetic behavior.