Three-Dimensional Magnetic Page Memory

The increasing need to store large amounts of information with an ultra-dense, reliable, low power and low cost memory device is driving aggressive efforts to improve upon current perpendicular magnetic recording technology. However, the difficulties in fabricating small grain recording media while maintaining thermal stability and a high signal-to-noise ratio motivate development of alternative methods, such as the patterning of magnetic nano-islands and utilizing energy-assist for future applications. In addition, both from sensor and memory perspective three-dimensional spintronic devices are highly desirable to overcome the restrictions on the functionality in the planar structures. Here we demonstrate a three-dimensional magnetic-memory (magnetic page memory) based on thermally assisted and stray-field induced transfer of domains in a vertical stack of magnetic nanowires with perpendicular anisotropy. Using spin-torque induced domain shifting in such a device with periodic pinning sites provides additional degrees of freedom by allowing lateral information flow to realize truly three-dimensional integration

Reproducible formation of single magnetic bubbles in an array of patterned dots

International audienceThe formation conditions of single magnetic bubbles through in-plane field demagnetizationare investigated in an array of Co/Ni circular dots by magnetic force microscopy andcompared to micromagnetic calculations. We demonstrate high success rates in nucleatingstable bubbles. The efficiency of single bubble formation is found to depend not only on thedot size, material thickness and intrinsic material parameters but also on the bubble nucleationpath. Experimental phase diagrams and micromagnetic calculations highlight the influenceof the starting in-plane field amplitude and dipolar interactions in stabilizing the bubble.The identification of a systematic procedure for controlling nucleation of single bubbles,multidomain states or a uniform state is important from a technological point of view, openinga path toward the realization of reprogrammable magnonic crystals for the control of spinwavepropagation

Observation of Magnetic Radial Vortex Nucleation in a Multilayer Stack with Tunable Anisotropy

International audienceRecently discovered exotic magnetic configurations, namely magnetic solitons appearing in the presence of bulk or interfacial Dzyaloshinskii-Moriya Interaction (i-DMI), have excited scientists to explore their potential applications in emerging spintronic technologies such as racetrack magnetic memory, spin logic, radio frequency nano-oscillators and sensors. Such studies are motivated by their foreseeable advantages over conventional micro-magnetic structures due to their small size, topological stability and easy spin-torque driven manipulation with much lower threshold current densities giving way to improved storage capacity, and faster operation with efficient use of energy. In this work, we show that in the presence of i-DMI in Pt/CoFeB/Ti multilayers by tuning the magnetic anisotropy (both in-plane and perpendicular-to-plane) via interface engineering and postproduction treatments, we can stabilize a variety of magnetic configurations such as Néel skyrmions, horseshoes and most importantly, the recently predicted isolated radial vortices at room temperature and under zero bias field. Especially, the radial vortex state with its absolute convergence to or divergence from a single point can potentially offer exciting new applications such as particle trapping/detrapping in addition to magnetoresistive memories with efficient switching, where the radial vortex state can act as a source of spin-polarized current with radial polarization. Magnetic skyrmions are spin configurations with a topology that has perpendicular-to-plane magnetization components at the core and the edges with opposite directions 1,2. They can be Bloch or Néel type depending on the chirality of the transition region between the core and the edges, being circular or radial, respectively 3. Unique properties of skyrmions such as their intrinsically small size, topological stability and efficient manipulation with much lower threshold current densities compared to conventional micromagnetic structures have recently attracted the attention of researchers to look for ways of utilizing them in technological applications. Envisioned skyrmionic devices 1,2 are expected to possess the benefits of combining storage, logic operations and microwave functionalities at the same level with efficient use of energy 4,5. Skyrmions appear due to Dzyaloshinskii-Moriya Interaction (DMI) in the bulk of chiral magnets (Bulk DMI), at the interface of heavy metal/ferromagnet thin film stacks (interfacial DMI) 6-8 or in perpendicular magnetic anisotropy materials as a result of long range dipolar interactions 9,10 in the presence of DMI as well as frustrated exchange and four spin exchange interactions 11. Bulk DMI arises as a result of lack of inversion symmetry in chiral magnets, whereas the interfacial DMI (i-DMI) stems from the interaction between ferromagnetic atoms and strong spin-orbit coupling (SOC) atoms of an adjacent heavy metal 12-14. I-DMI strength is param-eterized by a constant D and can be incorporated into the Landau-Lifshitz-Gilbert (LLG) equation competing with other energy terms such as exchange, anisotropy and magneto-static energies. The resulting micromagneti