  Defining the magnetic anisotropy for in-plane or out-of-plane easy axis in
ferrimagnetic insulators films by controlling the strain, while maintaining
high-quality surfaces, is desirable for spintronic and magnonic applications.
We investigate ways to tune the anisotropy of amorphous sputtered ultrathin
thulium iron garnet (TIG) films, and thus tailor their magnetic properties by
the thickness (7.5 to 60 nm), substrate choice (GGG and SGGG), and
crystallization process. We correlate morphological and structural properties
with the magnetic anisotropy of post-growth annealed films. 30 nm thick films
annealed at 600 {\deg}C show compressive strain favoring an in-plane magnetic
anisotropy (IPMA), whereas films annealed above 800 {\deg}C are under a tensile
strain leading to a perpendicular magnetic anisotropy (PMA). Air-annealed films
present a high degree of crystallinity and magnetization saturation close to
the bulk value. These results lead to successful fabrication of trilayers
TIG/Au/TIG, with coupling between the TIG layers depending on Au thickness.
These results will facilitate the use of TIG to create various in situ clean
hybrid structures for fundamental interface exchange studies, and towards the
development of complex devices. Moreover, the sputtering technique is
advantageous as it can be easily scaled up for industrial applications.
