Magnetic tunnel junctions with perpendicular magnetic anisotropy are investigated using a conductive atomic force microscope. The 1.23 nm Co 40 Fe 40 B 20 recording layer coercivity exhibits a size dependence which suggests single domain behavior for diameters ≤ 100 nm. Focusing on devices with diameters smaller than 100 nm, we determine the effect of voltage and size on the effective device anisotropy K eff using two different techniques. K eff is extracted both from distributions of the switching fields of the recording and reference layers, and from measurement of thermal fluctuations of the recording layer magnetization when a field close to the switching field is applied. The results from both sets of measurements reveal that K eff increases monotonically with decreasing junction diameter, consistent with the size dependence of the demagnetization energy density. We demonstrate that K eff can be controlled with a voltage down to the smallest size measured, 64 nm. PACS numbers: 85.75.-d,73.40.Gk,75.78.-n,75.70.-i 1 I. INTRODUCTION Magnetic tunnel junctions (MTJs) with perpendicular magnetic anisotropy (PMA) are an attractive building block for non-volatile memories. PMA MTJs (p-MTJs) show promisein terms of the key requirements for implementation into products competitive with current data storage and memory technologies: large tunnel magnetoresistance (TMR), low writing energy cost, non-volatility over ∼ 10 years, and scalability of these properties toward ∼ 1 Tbit/inch 2 densities. Room temperature TMR ratios greater than 100% have long existed in in-plane MTJs 1,2 . In state of the art in-plane MTJs, TMR in excess of 600% is achieved by controlling the diffusion of Ta in the film stack through the addition of boron to the magnetic electrodes 3 . Despite these achievements, in-plane MTJs suffer from scalability issues due to their dependence on shape anisotropy for thermal stability and the high energy cost of switching the magnetization by the spin transfer torque (STT) effect 4,5 . For in-plane MTJs, switching energies E sw = I 2 c Rt, where I c is the critical switching current, R is the resistance, and t is the length of the pulse, of approximately 10 µJ/bit were achieved for current pulses on the order of 10 ms 6 . This value was drastically reduced using nanosecond pulses, yielding E sw on the order of single pJ/bit in purely in-plane MTJs 7 . In high TMR p-MTJs the large out-of-plane demagnetization energy does not contribute to E sw 8 . Recently, TMR ratios up to 162% were obtained in p-MTJs by further controlling interlayer diffusion through the substitution of Ta with Mo in the film stack 9 . PMA is achieved when the CoFeB thickness is less than about 1.5 nm, so that the effective anisotropy K eff is dominated by the interfacial anisotropy between Fe in the CoFeB and oxygen in the MgO 10 . In such p-MTJs, switching energies of hundreds of fJ/bit were achieved in 60 nm × 170 nm ellipses 11 . One of the most promising aspects of p-MTJs is that the interface anisotropy can be controlled by applying a...

A technique for micromagnetic simulation of the magnetoelectric (ME) effect in Cr2O3 based structures has been developed. It has been observed that the microscopic ME susceptibility differs significantly from the experimentally measured values. The deviation between the two susceptibilities becomes more prominent near the Curie temperature, affecting the operation of the device at room temperature. A fully electric field controlled ME switching element has been proposed for use at technologically interesting densities: it employs quantum mechanical exchange at the boundaries instead of the applied magnetic field needed in traditional switching schemes. After establishing temperature dependent physics-based parameters, switching performances have been studied for different temperatures, applied electric fields, and Cr2O3 cross-sections. It has been found that our proposed use of quantum mechanical exchange favors reduced electric field operation and enhanced scalability while retaining reliable thermal stability.

Wave function penetration has significant impact on nanoscale devices having ultrathin gate oxide. Although wave function penetration effects on ballistic drain current and capacitance-voltage characteristics in nanoscale devices have been reported in literature, to the best of the authors' knowledge, effects of temperature on drain current incorporating with and without wave function penetration are yet to be studied. In this work, the impacts of temperature, gate dielectric and film thickness in wave function penetration on ballistic drain current of nanoscale double-gate (DG) MOSFETs are presented. The effects are observed using two-dimensional self-consistent solution of Schrödinger and Poisson equations. It has been obtained that temperature effect on drain current is greatly dependent on silicon surface orientation. Drain current of DG MOS-FETs fabricated on h110i surface is more sensitive to temperature compared to h001i surface. This has been obtained for both the cases with and without incorporating wave function penetration in silicon-gate oxide interface. Electrostatics behind this phenomenon has been explained from the transmission probability of electrons from source to drain which is largely influenced by temperature on h110i surface compared to h001i: Moreover, the transmission coefficient is significantly affected by wave function penetration in h110i than h001i surface. Both these demonstrate greater sensitivity of temperature and wave function penetration in h110i silicon surface orientation compared to h001i: Furthermore, gate dielectric with lower conduction band offset and device scaling with thin channel thickness tend to exhibit greater impact of wave function penetration.

Voltage-controlled switching of CoFeB/MgO magnetic tunnel junctions has been analyzed using micromagnetic simulation that includes thermal fluctuations and surface roughness. It is shown that the large samples typically studied experimentally switch by domain wall motion, nucleated at points where the CoFeB is slightly thicker. This is a consequence of small thickness variations producing large percentage changes in the anisotropy owing to the near balance of interface anisotropy and shape anisotropy in these films. It is also found that these films are likely never saturated at the experimental fields employed owing to the importance of thermal fluctuations in the near 2-D geometry.

Exchange bias in a magnetoelectric Cr2O3/ferromagnet system at finite temperature, based on the formation of a domain wall in Cr2O3, has been investigated using Monte Carlo simulation. It has been shown that the calculation of the exchange bias based on domain wall formation yields a more realistic value than that calculated using interfacial exchange coupling between Cr2O3 and the adjacent ferromagnet. Possible shortcoming of the magnetoelectric effect in setting the switchable exchange bias in the low temperature regime has also been demonstrated based on an energy threshold requirement. Specifically, it has been found that the magnetoelectric effect becomes intrinsically less effective in switching the exchange bias at low temperature, thus making the applicability of the system limited to only a certain temperature range.