SPIN

Flash memory has served as an important technology driver due to its many new applications. Despite the fact that NAND flash has out run lithography and other scaling barriers and thus is facing steep challenges, several innovative solutions are being developed to carry its momentum, and it continues to serve as a technology driver in the nanoelectronics era. New devices that are not based on charge storage, on the other hand, are promising to further boost system performance by offering low-power, high-density, and fast latency storage. These new developments should provide the next generation memory and storage solutions that will elevate system performance to a new level.

This paper reviews the progress made over the last few years in understanding the development of perpendicular magnetic tunneling junctions (pMTJs). The material systems for making pMTJs, including rare-earth/transition metal alloys, L1₀-ordered (Co, Fe)–Pt alloys, Co/(Pd, Pt) multilayers, and CoFeB–MgO crystallized structures, are briefly introduced. The fabrication processes of the MTJ devices are focused on, consisting of open-trench, etch-back and self-aligned techniques. The authors also propose a spin-torque nano-oscillator based on pMTJ, for application in GHz range telecommunications.

A new concept of an optical spin generation using bright and dark soliton conversion behaviors within a modified optical add–drop filters known as a PANDA ring resonator is proposed. The orthogonal solitons can be formed randomly within the system and detected simultaneously at the output ports. Under the resonant condition, the orthogonal solitons corresponding to the left-hand and right-hand solitons (photons) can be generated. Whenever a photon is absorbed by an object, an angular momentum of either +ℏ or -ℏ is imparted to the object, in which two possible spin states known as soliton spins are exhibited. Many soliton spins, i.e., many particles, dynamic spin and long distance spin transport using the proposed design are also discussed.

We show that inhomogeneity-induced magnetoresistance (IMR) in lightly doped silicon can be significantly enhanced through the injection of minority charge carriers, and then tuned by an applied current to have an onset at low magnetic fields. We designed an IMR device in which, the inhomogeneity is provided by the p–n boundary formed between regions where conduction is dominated by the minority and majority charge carriers respectively; application of a magnetic field distorts the current in the boundary region, resulting in large magnetoresistance. The room-temperature field sensitivity of our IMR device at low fields was remarkably improved, with magnetoresistance reaching 10% at 0.07 T and 100% at 0.2 T, approaching the performance of commercial giant magnetoresistance devices. The combination of high sensitivity to low magnetic fields and large high-field response should make this device concept attractive to the magnetic field sensing industry. Moreover, being based on a conventional silicon platform, it should be possible to integrate with existing silicon devices and so aid the development of silicon-based magnetoelectronics.

The use of polarized currents as tools for influencing the magnetic switching of magnetic materials was an important step in the evolution of modern recording technologies. A new paradigm was opened and new technologies based on this new idea have been developed. However, the modeling effort did not followed at the same pace the technological developments. In this paper, we are analyzing the effect on switching critical curves of the polarized current, which seems to be the most sensitive tool for the moment in evidencing these effects. The most important point of this paper is that we took into consideration the effect of higher order terms in the series expansion of the uniaxial anisotropy free energy and we analyze how these terms are influencing the critical curve shape. The results are discussed in terms of the efficiency of the polarized currents on the switching behavior of macrospins.

We used polarized neutron reflectometry (PNR) to investigate the depth-dependent saturation magnetization (4πM_s) of bi-layer structured Fe–N/Fe grown on MgO substrates, which were prepared by a facing target sputtering method followed by a subsequent annealing process to purposely study the N inter-diffusive effect. It is observed that by tuning the Fe layer thickness from 2 nm to 5 nm, the magnetic properties of the resulting product varies substantially. According to X-ray diffraction, an additional peak, indexed to Fe₁₆N₂(004), was developed in the sample with thinner (2 nm) underlayer. Its corresponding PNR study shows a 4πM_s of up to 2.82 T towards the substrate interface, which is 14% higher than the known limit (Fe₆₅Co₃₅ ~ 4πM_s = 2.45 T). We attribute this giant magnetization to the presence of chemically ordered Fe₁N₂. We have seen evidence that the high M_s is favorably stabilized due to the lattice misfit. The thickness range is consistent with the strained region of the films. This depth-dependent saturation magnetization analysis can shed a light to help understand the previous magnetization reports by classical magnetometry methods for the samples prepared using the same underlayer.

The dynamics of vortex gyration under spin-polarized current in a spin-torque nano-oscillator with axial symmetry violated by shape imperfection has been studied by micromagnetic modeling. We have considered the following kinds of shape: the displacement of the nanodisks centers, the pyramidal shape and the shape with several small cutouts. The corresponding frequency spectra of the vortex oscillations are presented. We found that shape imperfection can influence not only fundamental frequency but also can genarate second and higher harmonics. The impact of different types of shape on the vortex dynamics has been analyzed qualitatively. New ideas of microwave signal arising by artificial nonidealities of structure were proposed.

It has been known that magnetic properties of a ferromagnet grown on piezoelectric substrates can be altered by the electric field-induced strain. We consider spin-valve CoFe/Cu/CoFe/IrMn grown on (011)-cut piezoelectric Pb(Mg_1/3Nb_2/3)O₃–PbTiO₃ (PMN–PT) substrate and investigate the effect of the electric field on the giant magnetoresistance (GMR) of the spin valve. We found that the electric field induced strain on PMN–PT substrate enhances the coercivity of the magnetic layers. The transport measurement shows that the GMR ratio of the spin valve could be altered as much as 50% for an electric field of -8 kV/cm. The change of GMR is attributed to the reduced maximum degree of the antiparallel alignment between the magnetization directions of the free and pinned layers. The present studies establish a prototype electrically tunable magnetic memory device such that the electric field can reversibly tune spin valve magnetoresistance without deteriorating electric and magnetic properties.