Magnetic domain walls (DWs) in perpendicularly magnetised thin films are attractive for racetrack memories, but technological progress still requires further reduction of the operationing currents. To efficiently drive these objects by the means of electric current, one has to optimize the damping-like torque which is caused by the spin Hall effect (SHE). This not only requires a high net spin Hall angle but also the presence of a Dzyaloshinskii–Moriya interaction (DMI) to produce magnetic textures sensitive to this type of the torque. In this work, we explore the coexistence and importance of these two phenomena in epitaxial Pt/Co/Pt1−xAux films in which we control the degree of inversion symmetry-breaking between the two interfaces by varying x. Gold is used as a material with negligible induced magnetic moment and SHE and the interface between Co/Au as a source of a small DMI. We find no current-induced DW motion in the symmetric Pt/Co/Pt (x = 0) trilayer. By fitting a one-dimensional model to the DW velocity as a function of drive current density and in-plane applied field in samples with non-zero values of x, we find that both net DMI strength and spin Hall angle rise monotonically as Au is introduced. They reach values of 0.75 ± 0.05 mJ m−2 and 0.10 ± 0.01, respectively, for Pt/Co/Au (x = 1).
Focus on Spin Memory
Guest Editors
Jagadeesh Moodera, Massachusetts Institute of Technology
Markus Münzenberg , University of Greifswald
Scope
The concept of electron spin proposed by Samuel Goudsmit and George Uhlenbeck nearly 100 years ago has been revolutionising the information storage industry for the past two to three decades. In conventional electronics, charges are manipulated or stored by electric fields, with no attention paid to spin. Nevill Mott, who realised that spin could influence conduction in a ferromagnetic metal, introduced the idea of a two current model, spin-up (majority-spin) and spin-down (minority-spin) that set the early stage. The development of spintronics, exploiting the electron?? spin degrees of freedom in devices, the discovery of spin polarized current, GMR (giant magnetoresistance) and TMR (tunnel magnetoresistance) set the platform for strong technological advances. Spin orientation is maintained unless perturbed by a magnetic field or until its exchange interacts with another opposite spin (nuclear or electron) causing it to flip. The very fundamental property of the ferromagnet, namely the hysteresis and remanent magnetisation, allows for the non-volatile storage of information such as in magnetic random access memory (MRAM). On the other hand, momentum conservation by spin-orbit torques allows an efficient spin control. Spin textures and topological objects, such as skyrmions, guide new ways for rethinking magnetic memories and spin-based computation. Magnetic storage can be much more complex, thinking of spin textures instead of storing digital information as '0' and '1'. Thereby, non-linearities in the spin-memories allow to mimic neuron inspired learning and to think of alternative ways of intelligent data processing. The spin also facilitates a robust means to transmit information. In the form of spin-currents and spin-waves, information can be transferred. Besides the nonvolatility of spin-based memory, they are fast and potentially very energy efficient. Different device geometries and materials have been investigated, from oxide spintronics to organic molecules and graphene, from single magnetic molecules, spins in semiconductors and single rare earth atoms to miniaturise magnetic storage to the ultimate limit. New concepts also involve spin manipulation on temporal limits towards femtoseconds and even beyond.
The goal of this special issue is to bring out various approaches and progress in the field of spin memory, both from the fundamental science point of view and technological status, including where we are, the bottle necks, new concepts and the future direction.
Submission process and deadline for submission
All articles to feature in this Focus Collection are invited contributions, and authors who have agreed to submit should do so by visiting our online submission form.
The window for submissions is open from now until 31 June 2019. Nanotechnology is able to publish focus collections incrementally. This means that articles submitted early will be published as soon as they are accepted and prepared for publication, without being delayed waiting for other papers in the collection. If you are not able to meet the deadline, please let us know.