High-quality thulium iron garnet films with tunable perpendicular magnetic anisotropy by off-axis sputtering \u2013 correlation between magnetic properties and film strain

C N Wu,S R Yang,K Y Lin,C K Cheng,J Kwo,C T Wu,M Wu,S L Yeh,M Hong,C C Tseng,Y T Fanchiang,T Liu

doi:10.1038/s41598-018-29493-5

Abstract

Thulium iron garnet (TmIG) films with perpendicular magnetic anisotropy (PMA) were grown on gadolinium gallium garnet (GGG) (111) substrates by off-axis sputtering. High-resolution synchrotron radiation X-ray diffraction studies and spherical aberration-corrected scanning transmission electron microscope (Cs-corrected STEM) images showed the excellent crystallinity of the films and their sharp interface with GGG. Damping constant of TmIG thin film was determined to be 0.0133 by frequency-dependent ferromagnetic resonance (FMR) measurements. The saturation magnetization (Ms) and the coercive field (Hc) were obtained systematically as a function of the longitudinal distance (L) between the sputtering target and the substrate. A 170% enhancement of PMA field (H⊥) was achieved by tuning the film composition to increase the tensile strain. Moreover, current-induced magnetization switching on a Pt/TmIG structure was demonstrated with an ultra-low critical current density (jc) of 2.5 × 106 A/cm2, an order of magnitude smaller than the previously reported value. We were able to tune Ms, Hc and H⊥ to obtain an ultra-low jc of switching the magnetization, showing the great potential of sputtered TmIG films for spintronics.

Highlights

Utilizing the electron’s second fundamental characteristic—spin, advances in spintronic research such as spin-transfer torque (STT) and spin-orbit torque (SOT) have recently attracted enormous attention
We have examined the excellent crystallinity of thulium iron garnet (TmIG) films by spherical aberration-corrected scanning transmission electron microscope (Cs-corrected STEM), and determined the damping constant of the TmIG thin films by frequency-dependent ferromagnetic resonance (FMR) measurements
The cross-sectional TEM image and the energy-dispersive X-ray spectroscopy (EDS) element mapping images shown in Fig. 1(a) show the uniform composition distribution in each layer and show no obvious chemical intermixing at the interface of the TmIG/gadolinium gallium garnet (GGG) thin film

Summary

Introduction

Utilizing the electron’s second fundamental characteristic—spin, advances in spintronic research such as spin-transfer torque (STT) and spin-orbit torque (SOT) have recently attracted enormous attention. High-quality TmIG films pave the way towards ultra-low current-induced SOT for magnetization manipulation in ferromagnetic hetero-structures with high SOT efficiency, realizing the magnetization switching, magnetic oscillation and ultrafast chiral domain wall motion. These can be applied to data storage, magnetic random access memory, logic/memory utilizing domain wall[9]. As an alternative way to deposit oxide thin films, we have successfully utilized off-axis magnetron sputtering to grow high-quality TmIG films with excellent crystallinity and PMA on GGG(111)[13] and observed a negative magnetoresistance in TI/ TmIG hetero-structures, revealing time-reversal symmetry breaking in TI14. Our work of high-quality, highly tunable PMA TmIG films provides a new route to tailoring rare earth iron garnet films for spintronic application

Methods

Results

Conclusion