High thermal durability of Ru-based synthetic antiferromagnet by interfacial engineering with Re insertion

Synthetic antiferromagnets (SAFs), composed of Ru spacer with a Re insertion layer, reveal superior thermal stability up to 450 °C annealing, making the back-end of line process a wider manufacturing window and tolerance to integrate the perpendicular magnetic tunneling junctions (P-MTJs) into CMOS process. The coupling strength decays significantly for SAFs with single Ru spacer after annealing above 400 °C. Due to the characteristics of refractory metals, Re can behave as a diffusion barrier during annealing. Furthermore, the Re spacer can still keep reasonable RKKY coupling strength. Therefore, the SAFs with Ru/Re composite spacers exhibit higher RKKY coupling strength than Ru spacers after 450 °C annealing. In addition, we discovered the different enhancements for the upper and lower interfacial Re insertion, which was attributed to the varied defect formation at interfaces. The stacking fault was formed at the upper Ru/Co interface in as-deposited state. When Re was inserted at the upper interface, the diffusion between Co and Ru was significantly suppressed and the stacking fault can be eliminated during annealing, leading to enhanced interlayer coupling. Through the interfacial engineering, we may have more degrees of freedom to tune the SAF performance and thus enhance process compatibility of P-MTJ to the CMOS process.

Local and global energy barriers for chiral domain walls in synthetic antiferromagnet-ferromagnet lateral junctions

The current induced manipulation of chiral spin textures is of great interest for both fundamental research and technological applications1–3. Of particular interest are magnetic non-volatile memories formed from synthetic antiferromagnetic racetracks in which chiral composite domain walls (DWs), that act as data bits, can be efficiently moved by current4. However, overcoming the trade-off between energy efficiency, namely a low threshold current density to move the domain walls, and high thermal stability, remains a major challenge for the development of integrated chips with high reliability and low power consumption. Here we show that chiral DWs5–7 in a synthetic antiferromagnet-ferromagnet lateral junction, formed by local plasma oxidation, are highly stable against large magnetic fields whilst the DWs can be efficiently moved across the junction by current. Our approach takes advantage of the locality of current-driven torque on the small volume of a chiral DW and the globality of field-torque in the energy landscape, thereby leading to fundamentally distinct energy barriers for motion and stability. We find that the threshold current can be further decreased by tilting the junction across the racetrack while not affecting the high DW stability. Furthermore, we demonstrate that chiral DWs can be robustly confined within a ferromagnet region sandwiched on both their sides by synthetic antiferromagnets and yet can be readily injected into these regions by current. Our findings break the aforementioned trade-off between efficiency and stability, allowing for diverse and versatile DW-based memory, and logic, and beyond.

Skyrmions in Thin Films, Interfaces and Antiferromagnetism

Magnetic skyrmions are small whirling topological defects in a texture magnetization state. Their stabilization and dynamics depend strongly on their topological properties. Skyrmions are induced by non-centrosymmetric crystal structure of magnetic compounds and thin films. Skyrmions are extremely small, with diameters in the nanometer range, and behave as particles that can be created, moved and annihilated. This makes them suitable for information storage and logic technologies. Skyrmions had been observed only at low temperature, and mostly under large applied magnetic fields. An intense research in this field has led to the identification of skyrmions in thin-film and multilayer structures in these heterostrutres skyrmions are able to survive at room temperature and can be manipulated by electrical currents. Utilizing interlayer magnetic exchange bias with synthetic antiferromagnet with can be used to isolated antiferromagnetic skyrmions at room temperature. The development of skyrmion-based topological spintronics holds promise for applications in the writing, processing and reading functionalities at room temperature and can be extended further to all-electrical manipulation spintronics.

Spin-orbit torque switching of chiral magnetization across a synthetic antiferromagnet

The interfacial Dzyaloshinskii-Moriya interaction (DMI) holds promises for design and control of chiral spin textures in low-dimensional magnets with efficient current-driven dynamics. Recently, an interlayer DMI has been found to exist across magnetic multilayers with a heavy-metal spacer between magnetic layers. This opens the possibility of chirality in these three-dimensional magnetic structures. Here we show the existence of the interlayer DMI in a synthetic antiferromagnetic multilayer with both inversion and in-plane asymmetry. We analyse the interlayer DMI’s effects on the magnetization and the current-induced spin-orbit torque (SOT) switching of magnetization through a combination of experimental and numerical studies. The chiral nature of the interlayer DMI leads to an asymmetric SOT switching of magnetization under an in-plane magnetic field. Our work paves the way for further explorations on controlling chiral magnetizations across magnetic multilayers through SOTs, which can provide a new path in the design of SOT devices.