Detection of bottom ferromagnetic electrode oxidation in magnetic tunnel junctions by magnetometry measurements

Surface oxidation of the bottom ferromagnetic (FM) electrode, one of the major detrimental factors to the performance of a Magnetic Tunnel Junction (MTJ), is difficult to avoid during the fabrication process of the MTJ's tunnel barrier. Since Co rich alloys are commonly used for the FM electrodes in MTJs, over-oxidation of the tunnel barrier results in the formation of a CoO antiferromagnetic (AF) interface layer which couples with the bottom FM electrode to form a typical AF/FM exchange bias (EB) system. In this work, surface oxidation of the CoFe and CoFeB bottom electrodes was detected via magnetometry measurements of exchange-bias characterizations including the EB field, training effect, uncompensated spin density, and coercivity. Variations of these parameters were found to be related to the surface oxidation of the bottom electrode, among them the change of coercivity is most sensitive. Annealed samples show evidence for an oxygen migration back to the MgO tunnel barrier by annealing.Comment: 5 pages, 4 figues, submitted to J. Appl. Phy

Two-Loop O(αt2){\cal O}(\alpha_t^2) Corrections to the Neutral Higgs Boson Masses in the CP-Violating NMSSM

We present our calculation of the two-loop corrections of ${\cal O}(\alpha_t^2)$ to the neutral Higgs boson masses of the CP-violating Next-to-Minimal Supersymmetric extension of the Standard Model (NMSSM). The calculation is performed in the Feynman diagrammatic approach in the gaugeless limit at vanishing external momentum. We apply a mixed $\overline{\mathrm{DR}}$-on-shell (OS) renormalization scheme for the NMSSM input parameters. Furthermore, we exploit a $\overline{\mathrm{DR}}$ as well as an OS renormalization in the top/stop sector. The corrections are implemented in the Fortran code NMSSMCALC for the calculation of the Higgs spectrum both in the CP-conserving and CP-violating NMSSM. The code also provides the Higgs boson decays including the state-of-the-art higher-order corrections. The corrections computed in this work improve the already available corrections in NMSSMCALC which are the full one-loop corrections without any approximation and the two-loop ${\cal O}(\alpha_t \alpha_s)$ corrections in the gaugeless limit and at vanishing external momentum. Depending on the chosen parameter point, we find that the ${\cal O}(\alpha_t \alpha_s + \alpha_t^2)$ corrections add about 4-7% to the one-loop mass of the SM-like Higgs boson for $\overline{\mathrm{DR}}$ renormalization in the top/stop sector and they reduce the mass by about 6-9% if OS renormalization is applied. For an estimate of the theoretical uncertainty we vary the renormalization scale and change the renormalization scheme and show that care has to be taken in the corresponding interpretation

Crack propagation in concrete at very early ages

Surface defects and cracks in early-age concrete slabs have been observed to propagate under adverse conditions, impairing the performance and service life of these structures. However, the underlying mechanism of this form of crack propagation has remained largely unexplained, with very limited literature available. In this paper, simple yet sufficiently rigorous theoretical analyses of crack propagation in early-age concrete slabs, based on combined geotechnical engineering and fracture mechanics models, are presented. The results obtained clearly show how surface cracks can become unstable and propagate further, and either become stable again or develop through the full depth of the slab. They also convincingly demonstrate the roles of surface cracks and defects, pore moisture suctions and exposure conditions in this process. Importantly, the critical role of good construction practices in minimising this form of cracking is highlighted. These include proper compaction and effective curing as well as timely and adequate saw-cutting

Plastic cracking of concrete: The roles of osmotic and matric suctions

Plastic cracking of concrete is primarily attributable to desiccation by evaporation from unprotected surfaces. This causes high matric suctions to develop in the pore water in the voids adjacent to these surfaces. Dissolved salts in the pore water generate osmotic suctions. However, the effects of these suctions on the strength of plastic concrete are imperfectly understood. In this paper, equations describing total (matric plus osmotic) and osmotic suctions and the shear strength of desiccated particulate materials are discussed briefly. The development of suctions in desiccating fly ash and their effect on its shear strength are illustrated by experimental data. These show that matric suctions do but osmotic suctions do not affect the shear strength of fly ash and hence of comparable materials, including plastic concrete

Asymptotic Behavior of Ext functors for modules of finite complete intersection dimension

Let $R$ be a local ring, and let $M$ and $N$ be finitely generated $R$-modules such that $M$ has finite complete intersection dimension. In this paper we define and study, under certain conditions, a pairing using the modules \Ext_R^i(M,N) which generalizes Buchweitz's notion of the Herbrand diference. We exploit this pairing to examine the number of consecutive vanishing of \Ext_R^i(M,N) needed to ensure that \Ext_R^i(M,N)=0 for all $i\gg 0$. Our results recover and improve on most of the known bounds in the literature, especially when $R$ has dimension at most two