Strain-tuned magnetic anisotropy in sputtered thulium iron garnet ultrathin films and TIG/Au/TIG valve structures

Abstract

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 (7.5–60 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 °C show compressive strain favoring an in-plane magnetic anisotropy, whereas films annealed above 800 °C are under a tensile strain leading to a perpendicular magnetic anisotropy. Air-annealed films present a high degree of crystallinity and magnetization saturation close to the bulk value. These results lead to the 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 toward the development of complex devices. Moreover, the sputtering technique is advantageous as it can be easily scaled up for industrial applications.