The design of soft matter in which internal fuels or an external energy input can generate locomotion and shape transformations observed in living organisms is a key challenge. Such materials could assist in productive functions that may range from robotics to smart management of chemical reactions and communication with cells. In this context, hydrated matter that can function in aqueous media would be of great interest. Here, we report the design of hydrogels containing a scaffold of high–aspect ratio ferromagnetic nanowires with nematic order dispersed in a polymer network that change shape in response to light and experience torques in rotating magnetic fields. The synergistic response enables fast walking motion of macroscopic objects in water on either flat or inclined surfaces and also guides delivery of cargo through rolling motion and light-driven shape changes. The theoretical description of the response to the external energy input allowed us to program specific trajectories of hydrogel objects that were verified experimentally.

Current-induced spin-orbit torques (SOTs) are of interest for fast and energy-efficient manipulation of magnetic order in spintronic devices. To be deterministic, however, switching of perpendicularly magnetized materials by SOT requires a mechanism for in-plane symmetry breaking. Existing methods to do so involve the application of an in-plane bias magnetic field, or incorporation of in-plane structural asymmetry in the device, both of which can be difficult to implement in practical applications. Here, we report bias-field-free SOT switching in a single perpendicular CoTb layer with an engineered vertical composition gradient. The vertical structural inversion asymmetry induces strong intrinsic SOTs and a gradient-driven Dzyaloshinskii–Moriya interaction (g-DMI), which breaks the in-plane symmetry during the switching process. Micromagnetic simulations are in agreement with experimental results, and elucidate the role of g-DMI in the deterministic switching processes. This bias-field-free switching scheme for perpendicular ferrimagnets with g-DMI provides a strategy for efficient and compact SOT device design.

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In this paper we use a Terahertz (THz) time-domain system to image and analyze the structure of an artwork attributed to the Spanish artist Goya painted in 1771. The THz images show features that cannot be seen with optical inspection and complement data obtained with X-ray imaging that provide evidence of its authenticity, which is validated by other independent studies. For instance, a feature with a strong resemblance with one of Goya's known signatures is seen in the THz images. In particular, this paper demonstrates the potential of THz imaging as a complementary technique along with X-ray for the verification and authentication of artwork pieces through the detection of features that remain hidden to optical inspection.

Magnetic random-access memory (MRAM) based on voltage-controlled magnetic anisotropy in magnetic tunnel junctions (MTJs) is a promising candidate for high-performance computing applications, due to its lower power consumption, higher bit density, and the ability to reduce the access transistor size when compared to conventional current-controlled spin-transfer torque MRAM. The key to realizing these advantages is to have a low MTJ switching voltage. Here, we report a perpendicular MTJ structure with a high voltage-controlled magnetic anisotropy coefficient ~130 fJ/Vm and high tunnel magnetoresistance exceeding 150%. Owing to the high voltage-controlled magnetic anisotropy coefficient, we demonstrate sub-nanosecond precessional switching of nanoscale MTJs with diameters of 50 and 70 nm, using a voltage lower than 1 V. We also show scaling of this switching mechanism down to 30 nm MTJs, with voltages close to 2 V. The results pave the path for the future development and application of voltage-controlled MRAMs and spintronic devices in emerging computing systems.

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In this work, we show the enormous size effect on the ordering transition temperature, T O , in samples of CoFe 2 O 4 nanoparticles with diameters ranging from 1 to 9 nm. Samples were characterized by HRTEM and XRD analyses and show a bimodal particle size distribution centered at 3 nm and around 6 nm for "small" and "large" particles, respectively. The results and concomitant interpretation were derived from studies of the magnetization dependence of the samples on temperature at low and high magnetic fields and relaxation times using both dc and ac fields. The large particles show a typical superparamagnetic behavior with blocking temperatures, T B , around 100 K and a Curie temperature, T C , above room temperature. The small particles, however, show a colossal reduction of their magnetic ordering temperature and display paramagnetic behavior down to ∼10 K. At lower temperatures, these small particles are blocked and show both exchange and anisotropy field values above 5 T. The order of magnitude reduction in T O demonstrates a heretofore unreported magnetic behavior for ultrasmall nanoparticles of CoFe 2 O 4 , suggesting its further study as an advanced material.

There is accelerating interest in developing memory devices using antiferromagnetic (AFM) materials, motivated by the possibility for electrically controlling AFM order via spin-orbit torques, and its read-out via magnetoresistive effects. Recent studies have shown, however, that high current densities create non-magnetic contributions to resistive switching signals in AFM/heavy metal (AFM/HM) bilayers, complicating their interpretation. Here we introduce an experimental protocol to unambiguously distinguish current-induced magnetic and nonmagnetic switching signals in AFM/HM structures, and demonstrate it in IrMn3/Pt devices. A six-terminal double-cross device is constructed, with an IrMn3 pillar placed on one cross. The differential voltage is measured between the two crosses with and without IrMn3 after each switching attempt. For a wide range of current densities, reversible switching is observed only when write currents pass through the cross with the IrMn3 pillar, eliminating any possibility of non-magnetic switching artifacts. Micromagnetic simulations support our findings, indicating a complex domain-mediated switching process.