Highly Tunable Ferromagnetic 2D Electron Gases at Oxide Interfaces

Abstract

the fundamental interest of exploring the spin degree of freedom in unusual electronic environments, but also for exploiting magnetism and spin currents in multifunctional devices. [7,8] Ongoing studies of magnetic 2DEGs focus on novel applications, as well as the search for new magnetic phenomena via, e.g., doping and charge transfer, or imposing epitaxial strain via growth on substrates with different crystal symmetries and lattice parameters. [9][10][11][12][13][14] LaTiO 3 (LTO) and EuTiO 3 (ETO) are two antiferromagnetic (AFM) insulating oxides possessing closely lattice-matched perovskite structures. Along the (001) direction, LTO has formally alternating charged layers (La 3+ O 2-/Ti 3+ O 2-2 ) and ETO has charge-neutral layers (Eu 2+ O 2-/ Ti 4+ O 2-2 ), thus the LTO/ETO interface has

High-mobility spin-polarized two-dimensional electron gas at the interface of EuTiO3/SrTiO3 heterostructures

“…As shown in figure 1(d), the zero-field resistancetemperature (R-T) curve of the ETO/STO heterostructure shows a monotonic decrease upon cooling from 300 to 1.8 K, which suggests the metallic ground state of the ETO/STO heterostructure. In contrast, the resistance of high-quality ETO thin films grown on (LaAlO 3 ) 0.3 (Sr 2 AlTaO 6 ) 0.7 (LSAT) (001) substrates (supplementary figure S1) using the same preparation parameters show insulating behaviors and its value is too large to be measured below 200 K (blue curve in figure 1(d)), which is consistent with previous observations in ETO/LSAT heterostructures [16]. We note that a bare STO single-crystal substrate experienced the similar deposition process is also a semiconductor, as shown in our previous work [17].…”

“…MR at 1.8 K reaches ∼9% under a low magnetic field (B < 20 Oe). MR value is approximately one order of magnitude higher than those observed in LaTiO 3 /ETO (MR = 0.8%) [16], EuO/KTaO 3 (MR = 0.2%) [30], STO/LaTiO 3 (MR = 0.3%) [29], and NdTiO 3 /STO (MR = 1%) [31] 2DEG systems. The simultaneous occurrence of SdH oscillations and a large hysteretic MR at the same To explain the mechanism of the hysteretic MR, we further measured the MR of the ETO/STO heterostructure by applying in-plane magnetic field (B // film plane and B ⊥ I), and obtained similar MR vs. B curves (supplementary figure S3).…”

“…The 4.5 nm (∼11-12 unit cells) conducting interfacial layer with Ti 3+ ions mainly contribute to the interfacial ferromagnetism. For our 73 nm ETO film, most of the Eu 2+ spins shall order antiferromagnetically below 5.5 K, while the symmetry broken interfacial Eu 2+ -O layer neighboring to the top Ti 3+/4+ -O layer of the STO substrate would show ferromagnetic order due to the Ruderman-Kittel-Kasuya-Yosida (RKKY) exchange interaction between Eu spins and itinerant Ti-3d electrons [10,11,16,38]. The RKKY interaction can stabilize the ferromagnetic state when the carrier density of itinerant electrons exceeds 1.4 × 10 21 cm −3 [16,38].…”

“…For our 73 nm ETO film, most of the Eu 2+ spins shall order antiferromagnetically below 5.5 K, while the symmetry broken interfacial Eu 2+ -O layer neighboring to the top Ti 3+/4+ -O layer of the STO substrate would show ferromagnetic order due to the Ruderman-Kittel-Kasuya-Yosida (RKKY) exchange interaction between Eu spins and itinerant Ti-3d electrons [10,11,16,38]. The RKKY interaction can stabilize the ferromagnetic state when the carrier density of itinerant electrons exceeds 1.4 × 10 21 cm −3 [16,38]. The carrier density of our ETO/STO heterostructure (n (Hall) = 4.28 × 10 22 cm −3 ) is one order of magnitude higher than 1.4 × 10 21 cm −3 .…”

LaAlO3/SrTiO3 Heterointerface: 20 Years and Beyond

“…[111] Shin et al reported a ferromagnetic LTO/ETO 2DEG interface at temperatures up to 5.5 K even though the respective entities are inherently antiferromagnetic. [112] Apart from regulating the carrier concentration of the interfacial 2DEG, the interfacial magnetotransport can also be tuned by varying the thickness of the LTO overlayer. Thereby indicating that the anomalous Hall effect at the interface is directly intervened by the carrier concentration.…”