Magnetic skyrmions are promising candidates for the next generation of spintronic devices due to their small size and topologically protected structure. One challenge for using these magnetic states in applications lies on controlling the nucleation process and stabilization that usually requires an external force. Here, we report on the evidence of skyrmions in unpatterned symmetric Pd/Co/Pd multilayers at room temperature without prior application of neither electric current nor magnetic field. Decreasing the ferromagnetic interlayer thickness, the tuning of the physical properties across the ferromagnetic/non-magnetic interface gives rise to a transition from worm like domains patterns to isolated skyrmions as demonstrated by magnetic force microscopy. On the direct comparison of the measured and simulated skyrmions size, the interfacial Dzyaloshinskii-Moriya interaction (iDMI) was estimated, reveling that isolated skyrmions are just stabilized at zero magnetic field taking into account non-null values of iDMI. Our findings provide new insights towards the use of stabilized skyrmions for room temperature devices in nominally symmetric multilayers.

We have investigated the motion of vortex domain walls passing across non symmetric triangular notches in single Permalloy nanowires. We have measured hysteresis cycles using the focused magneto-optical Kerr effect before and beyond the notch, which allowed to probe beyond the notch the occurrence probability of clockwise (CW) and counter-clockwise (CCW) walls in tail-to-tail (TT) and head-to-head (HH) configurations. We present experimental evidence of chirality flipping provided by the vortex -notch interaction. With a low exit angle the probability of chirality flipping increases and here with the lowest angle of 15 o the probability of propagation of the energetically favored domain wall configuration (CCW for TT or CW for HH walls) is ≈ 75%. Micromagnetic simulations reveal details of the chirality reversal dynamics. arXiv:1409.6370v2 [cond-mat.mes-hall]

Magnetic skyrmions are small-sized spin textures with nontrivial topology that behave like charged particles under a spin-polarized current. The efficient use of skyrmions on the next generation of technological devices will depend on the controllable creation of sub-100 nm skyrmions, ideally without any external field. We report on the magnetic domains and skyrmions evolution in nanostructured ferrimagnetic Pt/CoGd/Pt multilayers discs at zero magnetic field and room temperature. The tuning of the magnetic structures is studied as a function of the disc size. The ferrimagnetic labyrinthine stripes are succeeded by the formation of multiple or single isolated ferrimagnetic skyrmions depending on the diameter of the disc. Multiple ferrimagnetic skyrmions present an average size of ∼120 nm, whereas single skyrmions ∼70 nm. It indicates a strong effect played by the confinement of the disc in modifying the skyrmions density and size. Our results shed light on the single ferrimagnetic skyrmion stability at zero magnetic field, which is a further drive in the realization of antiferromagnetic spintronic devices such as skyrmion-based spin torque nano-oscillators with implications in neuromorphic computing.