SPIN

Geometric asymmetry effect on vortex annihilation was investigated in series of submicro-scaled permalloy dots. By introducing the one-side-flat asymmetric shape into circular magnetic disks, the original degenerate signals of vortex annihilation for different chirality are separated into two different trajectories, where the asymmetry level is quantified by an excised angle. The separation of annihilation field for clockwise and counterclockwise vortex shows as a function of the excised angle. The asymmetry influence on the separation of annihilation field is discussed from the view of disk aspect ratio and flat boundary effect. Comparison of experimental results with numerical simulations is also presented.

Motivated by spintronic devices and their applications, we engineer a model to investigate the magnetic properties of the magnetic nano-alloy Fe${}_{1+x}$Co${}_{1-x}$. Where $x$ is the fraction of iron atoms Fe substituted by the cobalt Co atoms, $x=0$ corresponds to 50% Fe atoms and 50% Co atoms, this compound is then called equiatomic FeCo. The purpose of this work is to apply the Monte-Carlo Simulations (MCS), under Metropolis algorithm to predict the magnetic properties of such system. In a first step, we propose a model describing this system including different exchange coupling interactions. Then, we establish and analyze the ground state phase diagrams, in different planes. For non-null temperature values, applied MCS under the Metropolis algorithm. The behavior of both the magnetizations and the susceptibilities are illustrated as a function of temperature. Also the effect of the different exchange coupling interactions is studied and discussed. The hysteresis loops are presented and analyzed for specific values of temperature, exchange coupling interactions and concentrations.

Recent study in [C. C. Lin, Y. F. Gao, A. V. Penumatcha, V. Q. Diep, J. Appenzeller and Z. H. Chen, Acs Nano 8, 3807 (2014)], showed that the spin-transfer torque (STT) is enhanced by the asymmetry in a graphene lateral spin-valve structure. This lateral structure or geometry can be modeled by a four-terminal magnetic tunneling junction (MTJ) as opposite to the conventional two-terminal MTJ. In this paper, using the nonequilibrium Green’s function formalism (NEGF), we compare the anti-damping components of the STT in a similar nonconventional lateral one-dimensional MTJ with that in the conventional MTJ. We find that the lateral geometry renders enhanced anti-damping torques compared with the conventional one, provided that the barrier energy, the scattering length and the magnetization angle are in a certain parameter region. We also identify this parameter region in the presence of dephasing. The enhancement of the anti-damping torques declines when the scattering region is longer. For the four-terminal MTJ of larger scattering length, the dephasing can expedite the anti-damping torque.

We present the possibility of enhancing magnetoresistance (MR) by controlling nanoscale domain wall (DW) width in a planar nanowire array. Results based on micromagnetic calculations show that DW width decreases with increasing exchange bias field and decreases with reducing exchange interaction between neighboring nanowires. Fe/Fe₃O₄ nanowire arrays were grown on $c$-plane sapphire to demonstrate the feasibility of this concept, and an enhanced MR ratio of 3.7% was observed at room temperature. compared with flat and stepped Fe₃O₄ thin films.

We illustrate in this contribution the determination of the magnetic conductance across a nanocontact region defined by an isolated defect region joined between two mono-atomic leads ferromagnetically ordered. The system is described by the Heisenberg interaction. Additionally, to deal with the lack of symmetry across the contact region defined by the isolated defect, we involve the phase field matching approach. Furthermore, to compute the quantum conductance, we define the quantum scattering of the transmission and reflection probabilities within the framework of Landauer–Büttiker formalism. Based on these approaches, we present an analytical expression of the magnetic conductance. The obtained analytical results based on our adopted procedures confirm the known results adopted for perfect infinite leads (no defect). Our model calculations can be applied numerically when we deal with doping across the defect region. The adopted model could be also used numerically to deal with the impurity configurations that one might encounter in real systems.

The Magneto-Optic Kerr Effect (MOKE) technique has been used to investigate the magnetic properties of Ni thin films, with thickness $t$ ranging from 9 to 163nm, evaporated onto several substrates (glass, Si (111), mica and Cu) with and without an evaporated Cu underlayer. The MOKE observations were correlated with the surface morphology inferred from Scanning Electron Microscope images and with the structural properties (grain size and strain). Some interesting behaviors of the coercive field (with values in the 2 to 151 Oe range), the squareness (between 0.1 and 0.91) and the saturation field (25–320 Oe) are observed as a function of $t$, the substrate and the Cu underlayer. A thickness-dependent stress-induced anisotropy is found in these films. The differences between the present MOKE results and the ones obtained from the Vibrating Sample magnetometer (VSM) are highlighted. The former describe the surface magnetism of these systems, while the latter are attributed to the whole volume of the sample.

As CMOS technology scales down toward below 2-digit nanometer dimensions, exponentially increasing leakage power, vulnerability to radiation induced soft errors have become a major problem in today’s logic circuits. Emerging spin-based logic circuits and architectures based on nonvolatile magnetic tunnel junction (MTJ) cells show a great potential to overcome the aforementioned issues. However, radiation induced soft errors are still a problem in MTJ-based circuits as they need sequential peripheral CMOS circuits for sensing the MTJs. This paper proposes a novel nonvolatile and low-cost radiation hardened magnetic full adder (MFA). In comparison with the previous designs, the proposed MFA is capable of tolerating particle strikes regardless of the amount of charge induced to a single node and even multiple nodes. Besides, the proposed MFA offers low power operation, low area and high performance as compared with previous counterparts. One of the most important features suggested by the proposed MFA circuit is full nonvolatility. Nonvolatile logic circuits remove the cost of high volume data transactions between memory and logic and also facilitate power gating in logic-in-memory architectures.