SPIN

Spin-devices are switched by flipping spins without moving charge in space and this can lead to ultra-low-energy switching replacing traditional transistors in beyond Moore’s law era. In particular, the electric field-induced magnetization switching has emerged to be an energy-efficient paradigm. Here, we review the recent developments on ultra-low-energy, area-efficient, and fast spin-devices using multiferroic magnetoelectric composites. It is shown that both digital logic gates and analog computing with transistor-like high-gain region in the input-output characteristics of multiferroic composites are feasible. We also review the equivalent spin-circuit representation of spin-devices by considering spin potential and spin current similar to the charge-based counterparts using Kirchhoff’s voltage/current laws, which is necessary for the development of large-scale circuits. We review the spin-circuit representation of spin pumping, which happens anyway when there is a material adjacent to a rotating magnetization and therefore it is particularly necessary to be incorporated in device modeling. Such representation is also useful for understanding and proposing experiments. In spin-circuit representation, spin diffusion length is an important parameter and it is shown that a thickness-dependent spin diffusion length reflecting Elliott–Yafet spin relaxation mechanism in platinum is necessary to match the experimental results.

We report on our results obtained on the physical properties of B_xIn_yGa${}_{1-x-y}$N quaternary alloys in the zinc-blende phase that are thoroughly considered by the linearized augmented plane wave method, with a full potential within density functional theory, for different concentrations $x$ and $y$ as employed in the Wien2k code. We calculated the structural properties, including lattice constant $a_0$ and the bulk modulus $B$. We computed as well the band structures, the dielectric constant and the refractive index of our quaternary alloys compounds. Finally, nonlinear dependence on the compositions $x$ and $y$ are investigated in-depth and still expecting for experimental confirmations. To the best of our knowledge, this is the first theoretical investigation of B_xIn_yGa${}_{1-x-y}$N alloy conducted to date.

This study was to investigate theoretically the d°-d Half Heusler compound CrSbSr. We have adopted the first-principles full potential linearized augmented plane waves (FP-LAPW) method within GGA and mBJ-GGA potential. The calculated values of formation energy and elastic constants for the d^∘-d HH CrSbSr compound support the thermodynamic and mechanical stability. To the best of our knowledge, there are no available data to compare our results. The calculated lattice parameter and magnetic moments are in good agreement with the available works for VSbSr compound. The electronic structure within the GGA scheme indicates that the d^∘-d HH CrSbSr compound exhibits a spin gapless semiconductor behavior. This behavior was improved by using the mBJ-GGA potential, thus this compound can be a potential candidate for spintronic applications. We believe that our predictive results can be useful for future studies.

Full-Heuslers are a group of materials that have repeatedly attracted the curiosity of scientists and researchers, especially for their use in the field of spintronics. In this work, we undertook a study on the structural, elastic, electronic, magnetic and thermodynamic properties of the full-Heusler Mn₂OsGe alloy using the calculations of the first principles. Two approximations are used: the generalized approximation of the Perdew–Burke–Ernzerhof GGA–PBE gradient for electron-correlation exchange and the new modified Tran-Blaha form of the modified Becke-Johnson mBJ–GGA-PBE potential. As important results, we found that the compound Mn₂OsGe is stable in the CuHg₂Ti structure; on the other hand, we could also verify its mechanical stability at zero temperature and pressure. For the calculation of the electronic properties, we were able to determine the half-metallic ferrimagnetic character of our compound, which exhibits a metallic behavior in the state of the majority spins, and a semiconductor behavior in the state of the minority spins. An integer value of 2${\mu }_B$ has been recorded for a magnetic moment and this conforms to the Slater–Pauling rule.

The continuous downscaling in CMOS devices has increased leakage power and limited the performance to a few GHz. The research goal has diverted from operating at high frequencies to deliver higher performance in essence with lower power. CMOS based on-chip memories consumes significant fraction of power in modern processors. This paper aims to explore the suitability of beyond CMOS, emerging magnetic memories for the use in memory hierarchy, attributing to their remarkable features like nonvolatility, high-density, ultra-low leakage and scalability. NVSim, a circuit-level tool, is used to explore different design layouts and memory organizations and then estimate the energy, area and latency performance numbers. A detailed system-level performance analysis of STT-MRAM and SOT-MRAM technologies and comparison with 22nm SRAM technology are presented. Analysis infers that in comparison to the existing 22nm SRAM technology, SOT-MRAM is more efficient in area for memory size $\ge 128$KB, speed and energy consumption for cache size $\ge 32$KB. A typical 256KB SOT-MRAM cache design is 27.74% area efficient, 2.97 times faster and consumes 76.05% lesser leakage than SRAM counterpart and these numbers improve for larger cache sizes. The article deduces that SOT-MRAM technology has a promising potential to replace SRAM in lower levels of computer memory hierarchy.

The magnetic properties of amorphous Co${}_{100-x}$Zr_x films prepared by co-evaporation have been studied by means of vibrating sample magnetometry and ferromagnetic resonance. The temperature dependence of spontaneous magnetization $M_s$ in the low temperature range can be described using Bloch’s law. In addition, the spin wave stiffness constant, the distance between nearest magnetic atoms and the exchange interaction between cobalt and its nearest neighbors were calculated from the experimental results for $x=27$. Spin-wave resonance modes were obtained and the change of the resonant field as a function of the mode number $n$ obeys the so-called $n^2$ law perpendicular to the film plane at 300K.

Research Highlights

• •Electronic, magnetic, elastic and thermoelectric properties of RbCrC alloy are investigated.
• •Material is half-metallic, ductile and anisotropic in nature.
• •The total magnetic moment (3$\mu$B) obeys the Slater–Pauling rule.
• •The HM RbCrC compound is identified as potential candidate for spintronic applications.
• •ZT calculated values of 0.89 and 0.94 make RbCrC a promising thermoelectric material candidate for use in future devices.

The aim of this work is to investigate the half-metallicity behavior, elastic, thermodynamic and thermoelectric (TE) properties of the Heusler compound RbCrC using the generalized gradient approximation (GGA-PBE96) and the modified Becke–Johnson (mBJ) approach. The electronic band structures and density of states reveal that RbCrC is a half-metallic ferromagnet (HMF). The calculated total magnetic moment of 3$\mu$B follows the Slater–Pauling rule ($M_{\mathrm{\text{tot}}}=Z_{\mathrm{\text{tot}}}-8$). The half-metallicity character can be maintained in the 5.4–7.4 Å lattice constants range and the 0.8–1.2 $c$/$a$ ratio range. Existence of half-metallic ferromagnetism in RbCrC makes it a promising material for practical applications in the spintronic field. Also, the RbCrC exhibits a ductile and anisotropic behavior. The quasi-harmonic Debye model (QHDM) is used to calculate the thermodynamic properties. The BoltzTraP code which is based on semi-classical Boltzmann theory (SCBT) is applied for calculating TE properties. According to the obtained figure of merit values (ZT between 0.89 and 0.94 from 50 K to 800 K), the RbCrC alloy remains a good candidate for thermoelectric applications.

The influence of mild thermal annealing and nickel addition on the magnetic properties of Co–CoO multilayers is investigated. Co–CoO and CoNi–CoNiO multilayers were fabricated by radio-frequency magnetron sputtering and natural oxidation. Their magnetic properties have been studied via the magneto-optical Kerr effect and a vector network analyzer ferromagnetic resonance setup. The Co–CoO multilayers were annealed up to 90min at $250^{°}$C and they were found to be always in-plane magnetized. The value of Gilbert damping was evaluated. The multilayers after annealing or Ni addition show a small increase in coercivity without considerable changes in their anisotropy. The phenomenon of inverted hysteresis with negative remanence, with the field being applied perpendicular to the film plane, has been recorded. It was modeled with two coexisting magnetic moments with in-plane and perpendicular anisotropies, respectively.

The structural, elastic, electronic and magnetic properties of quaternary OsCrMnSb and IrCrMnSb Heusler alloys are performed employing ab initio electronic structure calculations. It has been identified that the Y_I type is the most stable structure among the three configurations for both OsCrMnSb and IrCrMnSb alloys in the magnetic state. The calculated cubic elastic constants show that these alloys fulfill the mechanical stability criteria. The band structures and density of state calculations reveal the half-metallic (HM) behavior of these alloys with a direct gap, and the half-metallicity is rather originated from the Cr-d states. Results on magnetic properties suggest that OsCrMnSb and IrCrMnSb are HM antiferromagnets. However, the inclusion of spin–orbit coupling affects strongly the IrCrMnSb alloy, losing its HM nature.