Ultrathin regime growth of atomically flat multiferroic gallium ferrite films with perpendicular magnetic anisotropy

Abstract

Room temperature magnetoelectric multiferroic thin films offer great promises for the spintronics industry. The actual development of devices, however, requires the production of ultrathin atomically smooth films of high crystalline quality in order to increase spin transfer efficiency. Using both high-resolution transmission electron microscopy and atomically resolved electron energy loss spectroscopy, we unveil the complex growth mechanism of a promising candidate, gallium ferrite. This material, with its net room-temperature magnetization of approximately 100 emu/cm 3 , is an interesting challenger to the antiferromagnetic bismuth ferrite. We obtained atomically flat gallium ferrite ultrathin films with a thickness control down to one fourth of a unit cell. Films with thicknesses as low as 7 nm are polar and show a perpendicular magnetic anisotropy of 3 × 10 3 J/m 3 at 300 K, which makes them particularly attractive for spin current transmission in spintronic devices, such as spin Hall effect based heavy-metal / ferrimagnetic oxide heterostructures.

Spin Current Transport in Hybrid Pt/Multifunctional Magnetoelectric Ga0.6Fe1.4O3 Bilayers

“…The roughness of a GFO layer of similar thickness (32 nm) deposited alone on a STO (111) substrate, without any Pt layer on top, had already been previously characterized, and is also of about 0.3 nm. 40 Observations of the heterostructure cross section by transmission electron microscope (TEM) (JEOL 2100 F) allowed confirming the low roughness of the Pt/GFO interface. A composition profile was measured across the interface by energy dispersive X-ray spectroscopy (EDS) and showed that interdiffusion is limited in this system and restricted to a less than 2 nm wide zone (Figure 1b).…”

“…The choice of STO as the substrate was dictated by the will to have the lowest number of in-plane variants, and we have recently demonstrated the possibility to have a layer-by-layer growth of highly crystalline GFO on this substrate. 40 The growth of such atomically flat GFO films is a prerequisite to high quality Pt/GFO interfaces. The GFO layer (ca.…”

12 Multiferroic heterostructures for spintronics

“…With the progress in growth techniques, new multiferroic magnetoelectric candidates have emerged as alternatives to BiFeO3-based heterostructures. For instance, GaFeO3 [24][25][26], exhibiting a higher magnetoelectric coefficient than the reference Cr2O3 material, can now be deposited as high quality thin films [27]. Similarly, layered materials such as Aurivillius phases [28,29], only recently grown in a single-crystalline epitaxial form [30], show robust ferroelectric properties in the ultrathin regime [30][31][32][33] in a structure that is compatible with long-range magnetic order [34,35].…”

Multiferroic heterostructures for spintronics

“…With the progress in growth techniques, new multiferroic magnetoelectric candidates have emerged as alternatives to BiFeO3-based heterostructures. For instance, GaFeO3 [24][25][26], exhibiting a higher magnetoelectric coefficient than the reference Cr2O3 material, can now be deposited as high quality thin films [27]. Similarly, layered materials such as Aurivillius phases [28,29], only recently grown in a single-crystalline epitaxial form [30], show robust ferroelectric properties in the ultrathin regime [30][31][32][33] in a structure that is compatible with long-range magnetic order [34,35].…”