Anisotropy and Current Control of Magnetization in SrRuO3/SrTiO3 Heterostructures for Spin-Memristors

Abstract

Spintronics-based nonvolatile components in neuromorphic circuits offer the possibility of realizing novel functionalities at low power. Current-controlled electrical switching of magnetization is actively researched in this context. Complex oxide heterostructures with perpendicular magnetic anisotropy (PMA), consisting of SrRuO3 (SRO) grown on SrTiO3 (STO) are strong material contenders. Utilizing the crystal orientation, magnetic anisotropy in such simple heterostructures can be tuned to either exhibit a perfect or slightly tilted PMA. Here, we investigate current induced magnetization modulation in such tailored ferromagnetic layers with a material with strong spin-orbit coupling (Pt), exploiting the spin Hall effect. We find significant differences in the magnetic anisotropy between the SRO/STO heterostructures, as manifested in the first and second harmonic magnetoresistance measurements. Current-induced magnetization switching can be realized with spin-orbit torques, but for systems with perfect PMA this switching is probabilistic as a result of the high symmetry. Slight tilting of the PMA can break this symmetry and allow the realization of deterministic switching. Control over the magnetic anisotropy of our heterostructures therefore provides control over the manner of switching. Based on our findings, we propose a three-terminal spintronic memristor, with a magnetic tunnel junction design, that shows several resistive states controlled by electric charge. Non-volatile states can be written through SOT by applying an in-plane current, and read out as a tunnel current by applying a small out-of-plane current. Depending on the anisotropy of the SRO layer, the writing mechanism is either deterministic or probabilistic allowing for different functionalities to emerge. We envisage that the probabilistic MTJs could be used as synapses while the deterministic devices can emulate neurons.

Tunable magnetic anisotropy in SrMnO3/SrRuO3 bilayers studied by angle and temperature dependence of magneto-transport

“…On the other hand, studies of SRO thin films grown on SrTiO 3 (STO) (001) substrates suggest a favorable perpendicular magnetic anisotropy with the easy axis normal to the film surface, along the [110] or direction. 11 A strong perpendicular anisotropy was also reported for SRO thin films on STO (110) substrates, 12,13 and systematic studies from Ziese 14 showed a biaxial magnetic anisotropy at low temperatures that rotate in different directions with increasing temperatures. This unique transformation of magnetic anisotropy in SRO is rooted in the crystalline anisotropy influenced by strong spin-orbit interactions and by the epitaxial strain imposed in the films.…”

Role of noncollinear spin texture driven z-torque in deterministic spin-orbit torque induced switching of perpendicular magnetization

“…Applying an additional external magnetic field parallel to the electric current is a commonly used method for achieving the deterministic switching. 2 However, all-electric manipulation of magnetization is essential for practical device applications, and therefore, many studies on field-free switching methods are under investigation by exploring a material and systemic engineering as follows: antiferromagnetic layer and exchange bias, [10][11][12][13] competing spin current layer, 14 and magnetic trilayer, 15,16 tilted magnetic anisotropy, [17][18][19][20][21][22][23] structural asymmetry, 24,25 Rashba symmetry breaking. 26 Utilizing a chirality can be one efficient approach for achieving field-free SOT induced magnetization switching deterministically and it is firstly observed using chiral nanomagnet by Z. Luo et al 27 And then H. Wu et al confirms the possibility of field-free switching of perpendicular magnetization by chiral symmetry breaking in wedged system.…”