SPIN

We have developed a random-number-generator (RNG) named “spin dice,” which employs the stochastic nature of spin-torque switching (STS) in a magnetic tunnel junction. The principle of the idea is that the switching probability first tuned around 0.5 is varied linearly with the applied current. After that, the switching results are converted into binary random numbers. We fabricated several types of “spin dice” by combining magnetic tunnel junctions and single-board microcomputer, and achieved generation speed of random numbers up to several hundred kbit/sec. Because STS is scalable and magnetic tunnel junctions have compatibility to semiconductor fabrication process, “spin dice” can be considered as a promising candidate for truly random-number-generator (TRNG) for security applications.

Owing to improved thermal stability and scalability, materials with perpendicular magnetic anisotropy (PMA) are extremely attractive. The all perpendicular magnetic tunnel junction ($p$-MTJ) devices are primarily devoted to spin transfer torque (STT)-induced switching and few works report their microwave emission. Here, we demonstrate the basic results of RF function in nanoscale $p$-MTJ which has two different thickness free layers separated by atom-thick tungsten insertion. The ultrathin W spacer layer not only enables the two CoFeB free layers precess as a single layer but also greatly enhances the PMA which further induces high-emission frequency. The all perpendicular spin transfer torque nano-oscillator (STNO) exhibited high frequency (7.6GHz) and large current modulation capability of $0.86\mathrm{\text{GHz}}\cdot {\mathrm{\text{mA}}}^{-1}$ at moderate external magnetic field. Along with our previous work on STT switching utilizing the similar stack, such a multifunctional structure could bring low cost solutions to Internet of Things (IoT) network applications.

Spin-torque nano-oscillators (STNOs) have become one of the emerging and novel microwave devices with the high performance and tunability of GHz range frequency. The nanopillar structure with an out-of-plane (OP) spin polarizer and an in-plane (IP) magnetized free layer (FL) has been considered as a good candidate for the STNOs. Using the local rotational coordinate transformation, a nonstationary process describing magnetization dynamics in the laboratory frame is therefore transformed into a stationary one in the rotating frame. In this way, the state phase diagram of this type of STNOs is well established as a function of an applied current and external field, which is also evidenced by the macrospin simulations. Also, we show that the frequency tunability of the STNOs through electrical current can be well elevated by applying a static magnetic field anti-parallel to the spin-polarizer vector.

Understanding the dynamic behavior of an isolated skyrmion with external perturbations has been obstructed due to the difficulty in experimentally observing such an instantaneous phenomenon within picoseconds. Herein, we theoretically investigated the spin-transfer-torque-induced dynamics of an isolated skyrmion excited by external nanosecond-pulse perturbations. It is found that a redshift of the resonant frequency appears under a pulse polarized current with $\sim 50\times 10^{10}$A/m² and $>0.93$GHz, while a blueshift is presented under a combined perturbation of the pulse polarized current and an out-of-plane ac magnetic field. The physic origins of the redshift and the blueshift are ascribed to the increased average energy of system from $1.69\times 10^{-17}$J to $1.78\times 10^{-17}$J and integer multiple (twofold and fourfold) oscillation frequencies of total energy, respectively. The present study could thus provide an insight to the micromagnetic dynamics of skyrmion under the magnetoelectric couplings.

Magnetic phase stability and electronic properties of Gd-doped Mg₂X ($\mathrm{\text{X}}=\mathrm{\text{Si}}$, Ge and Sn) were investigated by first-principle calculations based on density functional theory. The present calculations were performed using the Generalized Gradient Approximation (PBE-GGA) and the modified Becke–Johnson (mBJ-GGA). The 4$f$ electrons’ behavior has been investigated as a function of the Coulomb repulsion $U$ by varying it from 0eV to 8eV. The ground state properties for the pure compounds are consistent with experimental values and other theoretical data. All doped compounds are metallic and ferromagnetic with large Curie temperature values. It was found that both exchange potentials ($\mathrm{\text{GGA}}+U$ and $\mathrm{\text{mBJ}}+U$) provide a better description of the electronic structures of pure and doped systems than regular GGA and mBJ.

The 4-2 compressor has been widely employed in the design of multipliers. The considerable impact of 4-2 compressors on the efficiency of multipliers has created significant research interests in design of new compressor structures. In the vast range of error resilient applications, multiplication plays an important role in performing computation. Imprecise (approximate) realization of multiplication results in considerable area, power and delay efficiency at the cost of negligible computational errors. In this paper, an imprecise 4-2 compressor is presented. Spintronic devices as promising alternative technologies for silicon-based FET are considered for implementation of the proposed design. All designs are simulated exhaustively at the circuit level and application level. The conducted simulations indicate the superiority of the proposed design compared with the related state-of-the-art in all aspects. The proposed design has more than two and three times lower power and power delay product, respectively, compared to the best previous design.

A new all-$d$-metal full-Heusler alloy (Cd₂MnPd) was designed based on density functional theory. Its crystal structure, band structure, density of states, magnetism, and the possibility of martensitic transformation were studied. The calculated total energy shows that the most stable cubic structure of this alloy is the L2₁ type at ferromagnetic (FM) state, and the equilibrium lattice constant is 6.57Å. The band structure and density of states show that it is a FM metal with a total magnetic moment of 3.97${\mu }_B$, mainly originating from the Mn element. The results of the martensitic transformation investigation show that the martensitic phase has minimum energy when the c/a ratio is 1.35, and the absolute value of the energy difference ($\mathrm{\Delta }{E}_M$) between the martensitic and the austenitic phases is 0.07eV. This indicates that there is a high possibility that a stable martensitic phase exists. Furthermore, $\mathrm{\Delta }{E}_M$ can be tuned by uniform strain, and the absolute value of $\mathrm{\Delta }{E}_M$ increases as the volume increases in the range of $V_{\mathrm{\text{opt}}}\pm 3\%V_{\mathrm{\text{opt}}}$ ($V_{\mathrm{\text{opt}}}$ is the optimal volume, namely, the cubic volume under its equilibrium lattice). In conclusion, Cd₂MnPd may be a good candidate for ferromagnetic shape-memory alloys (FSMAs). We expect that our theoretical prediction can provide guidance for exploring valuable FSMAs experimentally.

Deep submicron conventional complementary metal oxide semiconductor (CMOS) technology is facing various issues such as high static power consumption due to the increasing leakage currents. In recent years, spin-based technologies like magnetic tunnel junctions (MTJ) have emerged and shown some fascinating features to overcome the aforesaid issues of CMOS technology. The hybrid MTJ/CMOS circuits offer low power consumption, nonvolatility, and high performance. This paper proposes two novel hybrid MTJ/CMOS approximate full-adder circuits (AXMA) for low power approximate computing-in-memory architectures. The proposed AXMAs offer low area, high sensing speed, considerable lower energy consumption, and the lowest power delay product (PDP) than the considered antecedent counterparts. The proposed AXMAs also introduce the advantage of full nonvolatility to the systems. This feature allows the system to be powered off during the idle modes in order to reduce the static power without the need for any retention parts or loss of data. Applications of the proposed AXMAs in digital image processing and their effect on the quality of images considering some relevant metrics like peak signal-to-noise ratio (PSNR) and mean structural similarity (MSSIM) are also investigated using the MATLAB software.

The structural, electronic and magnetic properties of FeCr₂O₄ and CrFe₂O₄ spinels have been investigated by the first-principles approach based on density functional theory (DFT) and the full-potential linearized augmented plane-wave method, within the generalized gradient approximation (GGA-PBE) and GGA-$\mathrm{\text{PBE}}+U$ scheme. The stability of these spinels in the normal and inverse phases is evaluated.

The spin-polarized electronic band structures and density of states of FeCr₂O₄ calculated by GGA-PBE and GGA-$\mathrm{\text{PBE}}+U$ show that the minority spin channel has metallic nature and the majority spin channel has a half-metallic (HM) gap of 0.25eV and 1.30 eV, respectively. CrFe₂O₄ shows that both minority and majority spin channels have metallic nature when using GGA-PBE and half-semiconducting behavior with half-semiconductor gap of 0.71eV when using GGA-$\mathrm{\text{PBE}}+U$, with magnetic moment of 2${\mu }_B$ per formula unit. Analysis of density of states of these compounds indicates that the magnetic moment mainly originates from the strong spin-polarization of 3$d$ states of Fe and Cr atoms. Presence of HMF in FeCr₂O₄ and CrFe₂O₄ spinels makes these compounds promising compounds for spintronic applications.

We are attempting to study the properties of new materials based on Diamond-like semiconductors (DLS). Due to broad collection of useful properties, DLS are exciting materials to study. The novel substances Li₂MnGeS₄ and Li₂CoSnS₄ result from using a rational and guileless design approach that leads the discovery of DLSs with wide-ranging regions of optical transparency. So here, we have analyzed their applications in atomic devices and system called “optoelectronic” using the FP-APW method and mBJ method. The band gap value for Li₂MnGeS₄ is 2.911eV and Li₂CoSnS4 is 2.45eV. The present DLS materials confirm their semiconductor characters. The presence of iron and manganese in these compounds have generated magnetic properties that we explored by the calculation of magnetic moment and spin-densities maps.

We study here a single band Hamiltonian model to describe the effect of next-nearest-neighbor (NNN) electron hopping on superconducting gap in Cuprates. The Hamiltonian consists of nearest-neighbor (NN) and next-nearest-neighbor (NNN) electron hopping integrals between the copper sides. By taking d-wave pairing symmetry into account, BCS type superconducting interaction is studied. By applying Zubarev’s Green function technique, the total Hamiltonian is solved. From the correlation function, the temperature-dependent superconducting gap (SC) equation is derived and is computed self-consistently by using technique $100\times 100$ grid points of the electron momentum. By varying SC coupling, chemical potential, J-T coupling parameter and second-nearest-neighbor electron hopping integral, the evolution of the order parameter is investigated.

A novel half-metallic family of materials, the multiple Dirac cones half-metals, has received considerable interest from researchers. Benefiting from its novel electronic structure, they are promising candidates for ultra-performance spintronic devices. In this paper, we propose a new half-metallic material, perovskite-type $R\stackrel{-}{3}c$ HoMnO₃, which possesses similar Dirac-like multiple linear band crosses. We investigated its electronic, magnetic and thermodynamic properties in detail on the basis of density functional theory. The excellent band structures are robust enough against spin-orbit coupling and electron and hole doping. Through calculations, we confirmed its multi-aspect stability. Based on the current study, we confirm that HoMnO₃ has potential for next-generation spintronic applications.

The effects of strain on the half-metallic (HM) and elastic properties of FeCrTe and CoCrSi alloys with Cl_b structure were calculated using a first-principles calculation. Both compounds showed (HM) property with full spin polarization, and this property can be present when their lattice constants are in the range from 5.18 Å to 5.71 Å for CoCrSi, and 5.25 Å to 6.05 Å for FeCrTe. The calculations of elastic properties show that both compounds are mechanically stable, ductile and hard with varied properties. In addition, calculations of the elastic characteristics for the above ranges for both FeCrTe and CoCrSi alloys showed mechanical stability, therefore, the FeCrTe and CoCrSi alloys are likely to be composed in experimental applications.

Magnetic skyrmions are promising building blocks for next generation data storage due to their stability, small size and extremely low currents to drive them. Skyrmion-based metallic racetrack memory has potential to replace traditional domain walls to store information as data bits, in which, however, skyrmions can drift from the direction of electron flow due to the Magnus force. In addition, skyrmion-edge effect at the end of the racetrack can cause the clogging of the skyrmions at the end of the racetrack. Here, we show that the clogging of skyrmion signals can be avoided by adding various kinds of notch at the end of the racetracks. On the other hand, by adding high-$K$ materials (materials with high magnetic crystalline anisotropy) at the edges, the skyrmions can be confined in the center region of the metallic racetrack successfully. This design can overcome the problems of both clogging and annihilation according to our micromagnetic simulation. As a result, skyrmions can pass the right end of the racetrack efficiently at a very high speed (100–300m/s), whereas the driving current is much smaller in comparison with other racetrack design. Besides, we study the influence of the uneven part at the joint of the high-$K$ material and the CoPt racetrack on the skyrmionic motion. It is found that at the joint between the high-$K$ material and the CoPt racetrack, the concave part basically does not affect the passage of skyrmion, but the convex part does when the length and width of the convex part reach a certain value. The results show that the design has high feasibility.

We consider theoretically the spin blockade effect on the spin polarization of a current passing through a geometrically confined head-to-head 180^∘ domain wall at a magnetic point contact in a two-dimensional (2D) metallic nanowire. The analysis is based on coherent scattering of the carriers by spin-dependent potential associated with the wall structure. The transmission properties of coherent states are obtained by introducing an algorithm to solve the coupled spin channels Schrödinger equation with mixed Dirichlet–Neumann boundary conditions applied far from the domain wall. It has been shown that a domain wall separating two media of opposite magnetization direction can act as a spin filter, allowing controllable modification of the spin polarization via the wall width.