Heat-assisted magnetic recording (HAMR) is being developed as the next-generation magnetic recording technology. High anisotropy granular media such as FePt-C have been demonstrated as HAMR media for ∼2 Tbpsi (terabits per in2) recording density. In order for this technology to reach its full potential of 4–5 Tbpsi, more progress and innovations are needed for the key requirements for HAMR media, including microstructure, design, magnetic distribution, and thermal design. Beyond granular media, heated-dot magnetic recording (HDMR) is planned to extend areal density toward 10 Tbpsi. HDMR combines similar advanced recording layer materials with advanced patterning techniques to fabricate <10-nm rectangular dot media.

The heat-assisted magnetic recording (HAMR) head–disk interface is a unique operating environment that combines nanoscale spacings, high shear rates, high-temperature gradients, and high optical fluxes in a mass-produced device. One of the greatest challenges is to develop materials for the head–disk interface that enable the required head–media spacing while also providing reliability. Traditional head–disk interface materials, engineered and optimized for conventional magnetic recording hard-disk drives, are challenged to provide the needed performance at the high temperatures that HAMR involves. We review some of the primary materials used in conventional magnetic recording, how high temperatures challenge their performance, and some of the current understanding and strategies to develop a reliable HAMR head–disk interface.

This article reviews progress in magnetoresistive (MR) read sensor technology for hard-disk drives (HDDs). MR reader technology has progressed from the anisotropic magnetoresistance sensor, to the current-in-plane giant magnetoresistive (CIP-GMR) sensor, to today’s current-perpendicular-to-plane (CPP) tunneling magnetoresistance (TMR) sensor. This evolution has driven the continuous growth of the areal density of HDDs from 2 Gbpsi (gigabits/in2) in early longitudinal recording to ∼1 Tbpsi (terabits/in2) currently in perpendicular magnetic recording. For further increases in the areal density, a transition to energy-assisted recording is expected in the near future. Further technical challenges for the read sensor technology toward 2 Tbpsi and then 5 Tbpsi areal densities are discussed based on recent promising experimental work on CPP-GMR using Heusler alloys, and CPP-GMR’s laterally expanded version, the lateral spin valve (LSV). To realize large MR output and narrow shield-to-shield spacing requirements for higher density recording, materials selection and optimization of interface structures of CPP-GMR and LSV devices are critical.

Specifically designed microlattices are able to combine outstanding mechanical and physical properties and, thus, expand the actual limits of the material property space. However, post-yield softening induced by plastic buckling or crushing of individual ligaments limits performance under cyclic loading, which affects their energy absorption capabilities. Understanding deformation under repeated loading is key to further optimizing these high-strength materials. While until now mainly hollow metallic microlattices and multistable or tailored buckling structures have been analyzed, this study investigates deformation and failure of polymer and ceramic-polymer microlattices under cyclic loading to understand the (i) influence of the microarchitecture and (ii) influence of processing conditions on the energy absorption capability. Despite fracture of individual struts, the stretching-dominated microarchitectures possess a superior behavior especially for larger cycle numbers. In combination with a specific annealing treatment of the polymer material, high recoverability and energy dissipation can be achieved.

We review two recent advances in coupled quantum mechanics/molecular mechanics (QM/MM) modeling for metallic materials. The QM/MM methods are formulated based on quantum mechanical charge density embedding. In the first method, QM/MM coupling is accomplished by an embedding potential evaluated via orbital-free density functional theory. The charge density embedding in the second QM/MM method is achieved through constrained density functional theory. The extension of QM/MM coupling to the quasicontinuum method is illustrated, offering a route toward quantum mechanical simulations of materials at micron scales and beyond. The theoretical formulations of the QM/MM methods are discussed in detail. We also provide some examples where the QM/MM methods have been applied to understand fundamental physics in a wide range of material problems, ranging from void formation, pipe diffusion along dislocation core, nanoindentation of thin films, hydrogen-assisted cracking, magnetism-induced plasticity to stress-controlled catalysis in metals. An outlook to future development of QM/MM methods for metals is envisioned.

We present a novel distributed-memory parallel implementation of the concurrent atomistic-continuum (CAC) method. Written mostly in Fortran 2008 and wrapped with a Python scripting interface, the CAC simulator in PyCAC runs in parallel using Message Passing Interface with a spatial decomposition algorithm. Built upon the underlying Fortran code, the Python interface provides a robust and versatile way for users to build system configurations, run CAC simulations, and analyze results. In this paper, following a brief introduction to the theoretical background of the CAC method, we discuss the serial algorithms of dynamic, quasistatic, and hybrid CAC, along with some programming techniques used in the code. We then illustrate the parallel algorithm, quantify the parallel scalability, and discuss some software specifications of PyCAC; more information can be found in the PyCAC user’s manual that is hosted on www.pycac.org.

We report on a new type of polymer electrolyte fuel cell based on a hydroxide ion conductive polymer combined with a non-noble chromium–nickel (Cr–Ni) catalyst for the oxygen reduction reaction (ORR). We study variable fractions of Cr in Ni by density functional theory simulating the thermodynamic potentials characterizing the ORR. We found increased ORR catalytic activity employing the rotating disk electrode technique. The polarization curve and power densities measured for the constructed fuel cell indicate considerable performance improvement with the Cr–Ni catalyst. Thus we expect that this kind of fuel cell may open up alternative routes in fuel cell research using non-noble catalysts.