Ultrafast electron diffraction of free standing expitaxial nickel oxide thin films

Spintronic devices incorporating antiferromagnetic materials have the potential to exhibit faster dynamics, a higher density of information storage, and more robustness to external magnetic fields than devices based on ferro or ferrimagnetic materials. However, these same advantages also make their static and dynamic properties difficult to probe, especially in thin films. To this end, we have fabricated freestanding antiferromagnetic thin films of nickel oxide (NiO) on SiN membranes to probe via ultrafast electron diffraction (UED). We show epitaxial growth of NiO on a water-soluble Sr₂CaAl₂O₆ buffer layer on SrTiO₃ substrates. After dissolving the sacrificial layer we transfer the free standing films to the SiN membranes and maintain the epitaxial character of the films. UED experiments were performed to probe the response of the lattice and potentially the magnetic order to optical excitations. We use an above-gap photoexcitation (l= 280 nm) and measure an initial lattice response on the order of picoseconds and the persistence of this state for greater than 20 ps. This work demonstrates the viability of the thin film transfer method combined with UED to probe the dynamic response of antiferromagnetic oxide thin films.