The growing market and massive use of Internet of Things nodes is placing unprecedented demands of energy efficient hardware for edge computing and microwave devices. In particular, magnetic tunnel junctions (MTJs), as main building blocks of spintronic microwave technology, can offer a path for the development of compact and high-performance microwave detectors. On the other hand, the fascinating field of skyrmionics is bridging together concepts from topology and spintronics. Here, we show the proof of concept of the direct electrical excitation and detection of the dynamics of a topological protected magnetic texture, i.e. skyrmion at room temperature and for a wide region of applied fields, including the zero field case. This topological spin torque diode is realized with an MTJ on top of a skyrmionic material. Quantitative Magnetic Force Microscopy measurements are employed to confirm the existence of a single skyrmion in the MTJ free layer. Spin torque diode electrical measurements show the electrical excitation via spin transfer torque (STT) of a skyrmion resonant mode with frequencies near 4 GHz and a selectivity one order of magnitude smaller than the uniform modes excited in the same device. Micromagnetic simulations identify these dynamics with the excitation of the breathing mode and point out the role of thickness dependent magnetic parameters (magnetic anisotropy field and Dzyaloshinkii Moriya interaction) in both stabilizing and exciting the magnetic skyrmions. This work marks a milestone for the development of topological spin torque diodes.

Synthetic antiferromagnetic structures can exhibit the advantages of high velocity similarly to antiferromagnets with the additional benefit of being imaged and read-out through techniques applied to ferromagnets. Here, we explore the potential and limits of synthetic antiferromagnets to uncover ways to harness their valuable properties for applications. Two synthetic antiferromagnetic systems have been engineered and systematically investigated to provide an informed basis for creating devices with maximum potential for data storage, logic devices, and skyrmion racetrack memories. The two systems considered are (system 1) CoB/Ir/Pt of N repetitions with Ir inducing the negative coupling between the ferromagnetic layers and (system 2) two ferromagnetically coupled multilayers of CoB/Ir/Pt, coupled together antiferromagnetically with an Ir layer. From the hysteresis, it is found that system 1 shows stable antiferromagnetic interlayer exchange coupling between each magnetic layer up to N = 7. Using Kerr imaging, the two ferromagnetic multilayers in system 2 are shown to undergo separate maze-like switches during hysteresis. Both systems are also studied as a function of temperature and show different behaviors. Micromagnetic simulations predict that in both systems the skyrmion Hall angle is suppressed with the skyrmion velocity five times higher in system 1 than system 2.

Magnetic skyrmions are localized magnetization entities with a particle-like feature due to the topological stability. Often considered as promising information carriers, they can exhibit a variety of dynamics beyond the rigid translational motion, such as breathing mode and gyration. These modes are at the key ingredient for skyrmion-based oscillators and detectors. These modes become even more interesting when considering skyrmions in magnetic multilayers. Here, we analyze, within a micromagnetic framework, the frequency response of skyrmions in different magnetic multilayers, as a function of the number of ferromagnetic repetitions and/or number of skyrmions. We observe the presence of a main frequency peak related to the breathing mode, as well as the emergence of additional peaks linked to the number of repetitions and skyrmions. Our achievement can be useful for the design of the next generation of microwave devices based on skyrmions. 1

Despite the huge recent interest towards chiral magnetism related to the interfacial Dzyaloshinskii Moriya interaction (iDMI) in layered systems, there is a lack of experimental data on the effect of iDMI on the spin waves eigenmodes of laterally confined nanostructures. Here we exploit Brillouin Light Scattering (BLS) to analyze the spin wave eigenmodes of non-interacting circular and elliptical dots, as well as of long stripes, patterned starting from a Pt(3.4 nm)/CoFeB(0.8 nm) bilayer, with lateral dimensions ranging from 100 nm to 400 nm. Our experimental results, corroborated by micromagnetic simulations based on the GPU-accelerated MuMax3 software package, provide evidence for a strong suppression of the frequency asymmetry between counter-propagating spin waves (corresponding to either Stokes or anti-Stokes peaks in BLS spectra), when the lateral confinement is reduced from 400 nm to 100 nm, i.e. when it becomes lower than the light wavelength. Such an evolution reflects the modification of the spin wave character from propagating to stationary and indicates that the BLS based method of quantifying the i-DMI strength from the frequency difference of counter propagating spin waves is not applicable in the case of magnetic elements with lateral dimension below about 400 nm.

We show that magnetic skyrmions can be stabilised at room temperature in continuous [Ir/Co/Pt]5 multilayers on SiO2/Si substrates without the prior application of electric current or magnetic field. While decreasing the Co thickness, a transition of the magnetic domain patterns from worm-like state to separated stripes is observed. The skyrmions are clearly imaged in both states using magnetic force microscopy. The density of skyrmions can be significantly enhanced after applying the “in-plane field procedure”. Our results provide means to manipulate magnetic skyrmion density, further allowing for the optimised engineering of skyrmion-based devices.

Different models have been used to evaluate the interfacial Dzyaloshinskii-Moriya interaction (DMI) from the asymmetric bubble expansion method using magneto-optics. Here, we investigate the most promising candidates over a range of different magnetic multilayers with perpendicular anisotropy. Models based on the standard creep hypothesis are not able to reproduce the domain wall (DW) velocity profile when the DW roughness is high. Our results demonstrate that the DW roughness and the interface roughness of the sample layers are correlated. Furthermore, we give guidance on how to obtain reliable results for the DMI value with this popular method. A comparison of the results with Brillouin light scattering (BLS) measurements on the same samples shows that the BLS approach often results in higher measured values of DMI.

The magnetisation data presented in the main text were acquired in a Quantum Design MPMS3 magnetometer. The magnetometer returns measurements of the total magnetic moment of the sample in emu. The total magnetic moment of the sample contains the contributions due to the substrate, thin film, and any spurious signal such as those described by Garcia et al. [1] . Careful sample handing was used to minimise spurious contributions to the total moment. The linear diamagnetic background due to the substrate was subtracted from the total measured moment. We report the data after substrate subtraction as the area normalised magnetic moment (moment/area) in emu/cm by measuring the area of the sample. For a uniform slab of ferromagnetic material, the volume magnetisation (M) can be determined by dividing the saturation moment/area by the thickness of the ferromagnetic layer. M can also be reliably determined by measuring several samples of varying thickness. If one plots moment/area versus thickness (d), as per Figure S1, then the fitted gradient will be M , moment/area = Md. (S1)

We report on the electrical transport properties of Nb based Josephson junctions with Pt/Co[Formula: see text]B[Formula: see text]/Pt ferromagnetic barriers. The barriers exhibit perpendicular magnetic anisotropy, which has the main advantage for potential applications over magnetisation in-plane systems of not affecting the Fraunhofer response of the junction. In addition, we report that there is no magnetic dead layer at the Pt/Co[Formula: see text]B[Formula: see text] interfaces, allowing us to study barriers with ultra-thin Co[Formula: see text]B[Formula: see text]. In the junctions, we observe that the magnitude of the critical current oscillates with increasing thickness of the Co[Formula: see text]B[Formula: see text] strong ferromagnetic alloy layer. The oscillations are attributed to the ground state phase difference across the junctions being modified from zero to [Formula: see text]. The multiple oscillations in the thickness range [Formula: see text] nm suggests that we have access to the first zero-[Formula: see text] and [Formula: see text]-zero phase transitions. Our results fuel the development of low-temperature memory devices based on ferromagnetic Josephson junctions.

Abstract We report on the electrical transport properties of Nb based Josephson junctions with Pt/Co $$_{68}$$ 68 B $$_{32}$$ 32 /Pt ferromagnetic barriers. The barriers exhibit perpendicular magnetic anisotropy, which has the main advantage for potential applications over magnetisation in-plane systems of not affecting the Fraunhofer response of the junction. In addition, we report that there is no magnetic dead layer at the Pt/Co $$_{68}$$ 68 B $$_{32}$$ 32 interfaces, allowing us to study barriers with ultra-thin Co $$_{68}$$ 68 B $$_{32}$$ 32 . In the junctions, we observe that the magnitude of the critical current oscillates with increasing thickness of the Co $$_{68}$$ 68 B $$_{32}$$ 32 strong ferromagnetic alloy layer. The oscillations are attributed to the ground state phase difference across the junctions being modified from zero to $$\pi $$ π . The multiple oscillations in the thickness range $$0.2~\leqslant ~d_\text {CoB}~\leqslant ~1.4$$ 0.2 ⩽ d CoB ⩽ 1.4 nm suggests that we have access to the first zero- $$\pi $$ π and $$\pi $$ π -zero phase transitions. Our results fuel the development of low-temperature memory devices based on ferromagnetic Josephson junctions.

We demonstrate a Josephson junction with a weak link containing two ferromagnets with perpendicular magnetic anisotropy and independent switching fields in which the critical current can be set by the mutual orientation of the two layers. Such pseudospin-valve Josephson junctions are a candidate cryogenic memory in an all superconducting computational scheme. Here, we use Pt/Co/Pt/CoB/Pt as the weak link of the junction with d(Co) = 0:6nm; d(CoB) = 0:3 nm, and d(Pt) = 5nm and obtain a 60% change in the critical current for the two magnetization configurations of the pseudospin-valve. Ferromagnets with perpendicular magnetic anisotropy have advantages over magnetization in-plane systems, which have been exclusively considered at this point, as, in principle, the magnetization and magnetic switching of layers in the junction should not affect the in-plane magnetic flux. Published under license by AIP Publishing.