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

Low frequency current and resistance fluctuations in magnetic tunnel junctions

Current and resistance fluctuations provide insight into the electronic and magnetic properties of spin electronic devices based on giant- and tunneling-magnetoresistance. The on going research on tunneling magnetoresistance (TMR) devices, namely magnetic tunnel junctions (MTJs), has revealed novel physics of spin dependent transport. To date, the majority of studies have involved conventional transport measurements and structural studies. Many studies are motivated by the desire to achieve higher TMR values as experimental observations of TMR are still well below theoretical predictions. The voltage bias dependence and temperature dependence of the TMR indicate that electronic transport in MTJs depends on structural quality. In particular, the role of defect states inside the barrier and interface effects are poorly understood. This thesis focuses on using noise as a complementary probe of magneto-electronic transport in MTJs. The emphasis is on relating barrier resistance noise and current shot noise to spin dependent transport processes in MTJs. Understanding and controlling noise is also important from a technological perspective. TMR devices are now being used as magnetic sensors in computer hard-drives and magnetoresistive random access memories. The trend towards miniaturization is leading to devices in which resistance and current noise become a limiting factor in their performance. 1/f resistance noise was measured over a wide range of magnetic fields and temperatures in a number of MTJs having both Mg O and AlOx tunnel barriers. The electronic 1/ f noise in MTJs is associated with defects in the tunnel barrier that act like charge traps. The temperature dependence of 1/f noise indicates that the population kinetics of charge traps are, in part, thermally activated and involve a broad distribution of charge trap depths. A Hooge-like noise parameter, α, is defined and it was found to exhibit an anomalous dependence on bias voltage, in contrast to the usual quadratic dependence found in metals and semiconductors. An exponential scaling between α and the differential resistance is revealed and indicates that the mechanisms behind the bias dependence of the differential resistance may also be responsible for the bias dependence of the barrier noise. Although the origin of such a scaling is not understood the data is consistent with a model for spin transport that involves the opening of low-noise, tunneling channels for electrons. Through this scaling, the measured bias dependence of the tunneling resistance quantitatively accounts for the bias dependence of the magnetoresistive 1/f noise that occurs when magnetization of the magnetic layers undergoes reversal. Current fluctuations in MTJs have also been investigated at low temperatures. For some MTJs, the current noise is in quantitative agreement with the shot noise predictions for random, uncorrelated tunneling events. However, other MTJs show shot noise suppression. Suppression is observed to be higher in thin barrier MTJs that also have large areas. Possibility defect assisted tunneling though localized states in the barrier is argued to be the reason for the suppression. Shot noise data in linear arrays of MTJs was found to be consistent with theoretical predictions of current noise for incoherent tunneling of charge carriers through N barriers; that is, a suppression of shot noise that scales with 1/N is observed

Molecular docking, Hirshfeld surface analysis and spectroscopic investigations of 1-(adamantan-1-yl)-3-(4-fluorophenyl)thiourea: A potential bioactive agent

SERT, YUSUF/0000-0001-8836-8667WOS: 000489698800014In this study, the optimized molecular structure, Hirshfeld surface analysis, vibrational frequencies and corresponding vibrational modes of a potential bioactive agent namely; 1-(adamantan-1-yl)-3-(4-fluorophenyl)thiourea were studied experimentally and theoretically. The theoretical calculations of the title compound were carried out using the density functional theory (DFT/B3LYP and DFT/M06-2X) quantum mechanical method with 6-311 + + G(d,p) basis set and Gaussian 09W program. The vibrational assignments of the title compound were obtained using VEDA 4 program by %10 precision with the help of potential energy distributions (PED). The experimental (FT-IR and Laser-Raman) spectra were recorded in solid phase at 4000-400 cm(-1) (FT-IR) and 4000-100 cm(-1) (Laser-Raman). Additionally, the experimental and theoretical H-1 and C-13 NMR chemical shifts in DMSO-d(6) and UV-Vis. Spectral analysis in DMF were studied theoretically and experimentally. The highest occupied molecular orbital (HOMO) and the lowest unoccupied molecular orbital (LUMO) analyses were performed. The molecular docking studies of the title compound revealed that it may exhibit antibacterial activity via inhibition of bacterial DNA gyrase PDB: 3U2D enzyme.Deanship of Scientific Research at Princess Nourah bint Abdulrahman University through the Research Group Program [RGP-1438-0010]This work was funded by the Deanship of Scientific Research at Princess Nourah bint Abdulrahman University through the Research Group Program (Grant No. RGP-1438-0010)

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