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We report on the fabrication of nanoscale, three-terminal in-plane spin–orbit torque switching devices with low switching current densities. Critical parameters in the fabrication process, including the ion beam etching angle and time, were optimized to avoid fabrication defects and improve device yield. Measurements of the magnetic field and current-induced switching behavior of the tunnel junctions demonstrate a sensitivity to the nanopillar aspect ratio, which dictates the nanopillars’ anisotropy and thermal stability. Additionally, we show that the current density required for switching can be reduced and the device thermal stability increased by inserting Hf interlayers into the heterostructure. Micromagnetic simulations are generally consistent with the experimentally observed switching behavior, suggesting an increase in the interfacial perpendicular anisotropy at the CoFeB/MgO interface and the reduction in the Dzyaloshinskii–Moriya interaction at the W/CoFeB interface by the Hf interlayers.

The Hi-C experiment can capture the genome-wide spatial proximities of the DNA, based on which it is possible to computationally reconstruct the three-dimensional (3D) structures of chromosomes. The transcripts of the long non-coding RNA (lncRNA) Xist spread throughout the entire X-chromosome and alter the 3D structure of the X-chromosome, which also inactivates one copy of the two X-chromosomes in a cell. The Hi-C experiments are expensive and time-consuming to conduct, but the Hi-C data of the active and inactive X-chromosomes are available. However, the Hi-C data of the X-chromosome during the process of X-chromosome inactivation (XCI) are not available. Therefore, the 3D structure of the X-chromosome during the process of X-chromosome inactivation (XCI) remains to be unknown. We have developed a new approach to reconstruct the 3D structure of the X-chromosome during XCI, in which the chain of DNA beads representing a chromosome is stored and simulated inside a 3D cubic lattice. A 2D Gaussian function is used to model the zero values in the 2D Hi-C contact matrices. By applying simulated annealing and Metropolis-Hastings simulations, we first generated the 3D structures of the X-chromosome before and after XCI. Then, we used Xist localization intensities on the X-chromosome (RAP data) to model the traveling speeds or acceleration between all bead pairs during the process of XCI. The 3D structures of the X-chromosome at 3 hours, 6 hours, and 24 hours after the start of the Xist expression, which initiates the XCI process, have been reconstructed. The source code and the reconstructed 3D structures of the X-chromosome can be downloaded from http://dna.cs.miami.edu/3D-XCI/.

A spin-torque switchable magnetic tunnel junction contains two ferromagnetic electrodes across a barrier that supports spin-polarized tunnel current. The spin-torque induced magnetic switching of its more agile, or “free” layer provides the “write” mechanism. Often the dynamics of the non-switching “reference” layer is also important. Here, we illustrate such dynamics involving both the free and the reference layers by using an exchange-coupled two-macrospin-moment numerical model, described by a set of Landau–Lifshitz–Gilbert (LLG) equations, together with a stochastic Langevin-field for finite temperature. Damping-like spin-transfer torque is included for both moments. In steady-state, the coupled precession is shown to reduce effective spin-current delivered to the free layer due to a precessional resonant spin-current back flow. This back-flow of spin current preferentially affects the parallel state dynamics. It is not directly related to the reference layer’s thermal stability, nor its spin-torque switching threshold, as determined by the total anisotropy energy and magnetic volume. Rather, the spin-current reduction relates primarily to the matching of precession frequency between the free- and the reference-layer. Therefore, a desirable materials choice is to avoid anisotropy fields giving the free and the reference layer similar dynamic frequencies, so as to prevent such resonance-related spin-current loss.

We define a new invariant tB(G) in bipartite graphs that is analogous to the toughness t(G) and we give sufficient conditions in term of tB(G) for the existence of k-factors in bipartite graphs. We also show that these results are sharp.