Growth-Induced Perpendicular Magnetic Anisotropy in Thin Film Rare Earth Iron Garnets

Abstract

Perpendicular magnetic anisotropy (PMA) is a property of magnetic films which allows for high-density data storage in spintronic applications. In rare earth iron garnets, PMA typically originates from magnetoelastic anisotropy either as a result of film strain due to lattice mismatch with a single crystal garnet substrate or from thermal mismatch upon annealing1. However, PMA derived from magnetoelastic anisotropy requires specific combinations of strain state and magnetostriction coefficients, so there is interest in finding new ways to control PMA in thin films.In this study we demonstrate that PMA can also be obtained from a dominant growth-induced anisotropy (GIA) using europium thulium iron garnet (EuTmIG) as a model material. By varying the ratio of Eu to Tm, the lattice parameter of the garnet can be changed, resulting in films which are under compression or tension on a gadolinium gallium garnet (GGG) substrate, as shown in Fig. 1 with high resolution x-ray diffraction (HRXRD) analysis. Vibrating sample magnetometry (VSM), shown in Fig. 2, indicates that PMA is present in all films regardless of strain state. We propose that PMA in the zero-strain film is attributed to GIA due to the preferential ordering of different rare earth ions on inequivalent lattice sites within the garnet2. Additionally, we quantify GIA and spin transport in the films with spin hall magnetoresistance measurements on Pt/EuTmIG hall crosses. This work shows that precise engineering of the structure of these high quality films creates new methods for control of garnet thin film properties for spintronic applications.  Fig. 1. HRXRD of the (444) symmetric reflection of ~25 nm EuIG, TmIG and Eu0.7Tm2.3Fe5O12 films on (111) GGG substrates show tensile, compressive, and near zero strain states, respectivley, as shown by the relative position of the film and substrate peaks.  Fig 2. PMA is evident in out-of-plane VSM of all films, regardless of the magnitude of magnetoelastic anisotropy.