New functionalities at oxide interfaces: Ultralow-power magnetization switching by orbital selection and high-mobility two-dimensional hole/electron transport*

We present our recent findings: 1) Low-power magnetization control utilizing peculiar electronic structures of magnetic perovskite oxide interfaces [1,2], and 2) realization of a high-mobility two-dimensional “hole” gas (2DHG) and electron gas (2DEG) at an oxide interface [3]. Both results are promising for future oxide-based electronics.
Bias-driven magnetization control of ferromagnets is highly desirable, but still challenging because generally electric-field effect is too weak to induce a large change in the magnetic anisotropy (MA) that is required for magnetization switching. Here, using a magnetic tunnel junction (MTJ) composed of La_0.67Sr_0.33MnO₃ (LSMO)/SrTiO₃ (STO)/LSMO, we demonstrate that a drastic change in the MA of LSMO can be induced when the chemical potential E_F at the LSMO/STO interface is moved between different orbital symmetry bands [1]. By this new approach, we have successfully realized a magnetic-field-free 90°-magnetization switching of LSMO by applying a small electric field of 0.05 V/nm. With changing V, the MA of the LSMO layer switches from two-fold symmetry to four-fold symmetry when the E_F is moved from the e_g band to the t_2g band. This change of MA is strong enough to rotate the magnetization without any assisting magnetic field, with an extremely small switching current density of ~ 10^–2 A/cm² [2]. Furthermore, we show our recent finding of a 2DHG with ultrahigh mobility up to 24,000 cm²V^–1s^–1 (at 2 K), which is realized by depositing a sub-nm-thick Fe layer (thickness ≦ 0.2 nm) on an STO surface. This is the highest hole mobility ever reported in oxide materials [3]. We found that the 2DHG/2DEG transport can be switched and controlled by the Fe thickness and gate voltage.
[1] L. D. Anh et al., Sci. Rep. 7, 8715 (2017). [2] L. D. Anh et al., Phys. Rev. Applied 12, 041001 (2019).[3] L. D. Anh et al, Adv. Mater. 32, 1906003 (2020).