Magnetism and spin transport in rare-earth-rich epitaxial terbium and europium iron garnet films

Rare-earth iron garnet thin films with perpendicular magnetic anisotropy (PMA) have recently attracted a great deal of attention for spintronic applications. Thulium iron garnet (TmIG) has been successfully grown and TmIG/Pt heterostructures have been characterized. However, TmIG is not the only rare-earth iron garnet that can be grown with PMA. We report the growth, magnetic, and spintronic properties of epitaxial terbium iron garnet (TbIG) and europium iron garnet (EuIG) thin films with PMA. Reciprocal space mapping shows the films are lattice matched to the substrate without strain relaxation, even for films up to 56 nm thick. The lattice strain and magnetostriction coefficient produce PMA in certain cases. TbIG grows on (111) gadolinium gallium garnet (GGG) with PMA due to the in-plane compressive strain, whereas TbIG on (111) substituted GGG (SGGG) is in tension and has an in-plane easy axis. EuIG grows with PMA on (100) and (111) GGG substrates, which facilitates the investigation of spintronic properties as a function of orientation. Both garnets have excess rare earth, which is believed to occupy Fe octahedral sites and in the case of TbIG is associated with an increase in the compensation temperature to 330 K, higher than the bulk value. Anomalous Hall effect (AHE) measurements of Pt/EuIG Hall crosses show that the spin mixing conductance of Pt/ (111) and (100) EuIG is similar. AHE measurements of Pt/TbIG Hall crosses reveal a sign change in the AHE amplitude at the compensation point analogous to all-metallic systems.

Figure 1

[(a)–(d)] High-resolution XRD ω-2θ scans of representative EuIG and TbIG thin films [(e) and (f)] High-resolution XRD reciprocal space maps of TbIG/GGG and TbIG/SGGG thin films.

Figure 2

(Tb,Eu) $3d$, Fe $2p$, and O $1s$ spectra of representative TbIG and EuIG thin films. In the RE spectra, peaks belonging to each oxidation state are marked.

Figure 3

In-plane (IP) and out-of-plane (OOP) VSM hysteresis loops of representative TbIG and EuIG thin films. In the IP EuIG hysteresis loops, the estimated anisotropy fields are presented and are color-coded (color online) in the same manner as the loops.

Figure 4

[(a)–(c)] Anomalous-Hall-like SMR hysteresis loops for Pt(4)/REIG(10) heterostructures. (d) Optical micrograph of representative Hall crosses used for data acquisition.

Figure 5

Temperature-dependent measurements of (a) magnetic moment, (b) Faraday rotation, (c) coercivity, and (d) AHE-like SMR amplitude. All of these techniques agree on a magnetic compensation point of ∼335 K.