Efficient bias-driven magnetization control by orbital selection at a La_0.67Sr_0.33MnO₃ interface

Bias-driven magnetization control of a ferromagnet, which utilizes the ability of controlling the magnetic anisotropy (MA) with an electric field, is crucial for spintronic applications due to its low power consumption. However, it remains a challenge to induce a large change in the MA of ferromagnetic materials that can rotate the magnetization. In this work, using La_0.67Sr_0.33MnO₃ (LSMO)/SrTiO₃ (STO)/LSMO magnetic tunnel junctions (MTJs), 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 bands with different orbital symmetries. By this new approach, we successfully realize a deterministic and magnetic-field-free 90°-magnetization switching of LSMO solely by applying a small electric field of 0.05 V/nm on the tunnel barrier, with a negligibly small current density of ~ 10^–2 A/cm².
The studied MTJs are grown on an STO (001) substrate by molecular beam epitaxy. We probe the orbital symmetry of the carriers and the MA of the LSMO layers at each bias V by measuring the magnetic-field-direction dependence of the tunneling conductance and that of the tunneling magnetoresistance (TMR), respectively. Using this approach, we show that, with applying V, the MA of the LSMO switches from a two-fold symmetry to a four-fold symmetry by shifting E_F from the e_g band to the t_2g band [1]. This change of MA is strong enough to rotate the magnetization direction from [110] to [1-10] without any assisting magnetic field. Our findings indicate that highly efficient magnetization control can be realized by designing materials so that the E_F lies close to the band edges of different-symmetry orbitals [2].
[1] L. D. Anh et al., Sci. Rep. 7, 8715 (2017). [2] L. D. Anh et al., Phys. Rev. Applied. 12, 041001 (2019).