Breaking of structural symmetries of nanomagnetic systems is of great interest for the development of ultralow-power spintronic devices. The structural asymmetry in various magnetic heterostructures has been engineered to reveal novel fundamental interactions between electric currents and magnetization, resulting in spin-orbit-torques (SOTs) on the magnetization [1][2][3][4][5][6] , which are both fundamentally important and technologically promising for device applications. Such SOTs have been used to realize current-induced magnetization switching [2][3][4]7 and domain-wall 3 motion [8][9][10] in recent experiments. Typical heterostructures exhibiting SOTs consist of a ferromagnet (F) with a heavy nonmagnetic metal (NM) having strong spin-orbit coupling on one side, and an insulator (I) on the other side (referred to as NM/F/I structures, shown schematically in Fig. 1a, which break mirror symmetry in the growth direction). In terms of device applications, the use of SOTs in NM/F/I structures allows for a significantly lower write current compared to regular spin-transfer-torque (STT) devices 4 . It can greatly improve energy efficiency and scalability [1][2][3][4][5]11 for new SOT-based devices such as magnetic random access memory (SOT-MRAM), going beyond state-of-the-art STT-MRAM.For practical applications, a critical requirement to achieve high-density SOT memory is the ability to perform SOT-induced switching without the use of external magnetic fields, in particular for perpendicularly-magnetized ferromagnets, which show better scalability and thermal stability as compared to the in-plane case 12 .However, there are currently no practical solutions that meet this requirement. In NM/F/I heterostructures studied so far, the form of the resultant current-induced SOT alone does not allow for deterministic switching of a perpendicular ferromagnet, requiring application of an additional external in-plane magnetic field to switch the perpendicular magnetization [2][3][4] . (This is a very general feature of SOT devices, which can be explained by symmetry-based arguments, as discussed below). In such experiments, the external field allows for each current direction to favor a particular orientation for the out-of-plane component of magnetization, thereby resulting in deterministic perpendicular switching. However, this external field is undesirable 4 from a practical point of view. For device applications, it also reduces the thermal stability of the perpendicular magnet by lowering the zero-current energy barrier between the stable perpendicular states, resulting in a shorter retention time if used for memory.This work provides a solution to eliminate the use of external magnetic fields, bringing SOT-based spintronic devices such as SOT-MRAM closer to practical application. We present a new NM/F/I structure, which provides a novel spin-orbit torque, resulting in zero-field current-induced switching of perpendicular magnetization. Our device consists of a stack of Ta/Co 20 Fe 60 B 20 /TaO x layers, but also has a...

We investigate the quantum anomalous Hall Effect (QAHE) and related chiral transport in the millimetersize (Cr 0.12 Bi 0.26 Sb 0.62 ) 2 Te 3 films. With high sample quality and robust magnetism at low temperatures, the quantized Hall conductance of e 2 /h is found to persist even when the film thickness is beyond the twodimensional (2D) hybridization limit. Meanwhile, the Chern insulator-featured chiral edge conduction is manifested by the non-local transport measurements. In contrast to the 2D hybridized thin film, an additional weakly field-dependent longitudinal resistance is observed in the 10 quintuple-layer film, suggesting the influence of the film thickness on the dissipative edge channel in the QAHE regime. The extension of QAHE into the three-dimensional thickness region addresses the universality of this quantum transport phenomenon and motivates the exploration of new QAHE phases with tunable Chern numbers.In addition, the observation of the scale-invariant dissipationless chiral propagation on a macroscopic scale makes a major stride towards ideal low-power interconnect applications.

Correlation of the surface physicochemical properties of nanoparticles with their interactions with biosystems provides key foundational data for nanomedicine. We report here the systematic synthesis of 2, 4, and 6 nm core gold nanoparticles (AuNP) featuring neutral (zwitterionic), anionic, and cationic headgroups. The cellular internalization of these AuNPs was quantified, providing a parametric evaluation of charge and size effects. Contrasting behavior was observed with these systems: with zwitterionic and anionic particles, uptake decreased with increasing AuNP size, whereas with cationic particles uptake increased with increasing particle size. Through mechanistic studies of the uptake process we can attribute these opposing trends to a surface-dictated shift in uptake pathways. Zwitterionic NPs are primarily internalized through passive diffusion, while the internalization of cationic and anionic NPs is dominated by multiple endocytic pathways. Our study demonstrates that size and surface charge interact in an interrelated fashion to modulate nanoparticle uptake into cells, providing an engineering tool for designing nanomaterials for specific biological applications.

Exosomes constitute an emerging biomarker for cancer diagnosis since they carry multiple proteins reflecting the origins of parent cells. Assessing exosome surface proteins provides a powerful means of identifying a combination of biomarkers for cancer diagnosis. We report a sensor platform that profiles exosome surface proteins in minutes by the naked eye. The sensor consists of a gold nanoparticle (AuNP) complexed with a panel of aptamers. The complexation of aptamers with AuNPs protects the nanoparticles from aggregating in a high salt solution. In the presence of exosomes, the non-specific and weaker binding between aptamers and the AuNP is broken, and the specific and stronger binding between exosome surface protein and the aptamer displaces aptamers from the AuNP surface and results in AuNP aggregation. This aggregation results in a color change of AuNP, and generate patterns for identification of multiple proteins on the exosome surface.