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We present the first Embedded Spin-Transfer-Torque MRAM (eMRAM) technology in a 14 nm CMOS node. A novel integration supports the highest eMRAM density (0.0273 um2 cell size), optimal magnetic tunnel junction (MTJ) placement between M1-M2 for performance and density, and the lowest-cost integration scheme, with only 3 added mask levels (2 critical + 1 non-critical) and a single added electrode module. An advanced 400°C-compatible MTJ stack is read and written by innovative reference-cell sensing circuitry. We demonstrate digital functionality and write performance down to 4 ns, with companion parametric analysis for magnetoresistance, switching voltage, retention, and endurance cycling. Finally, we checked the 14 nm eMRAM hardware BEOL EM and TDDB at the critical levels, verifying good reliability after the embedding process.

This paper presents a multi-step process to improve the stability of plasma ignition of a magnetic target in a multi-cathode physical vapor deposition (PVD) system. Most target materials in the system have no issues igniting a stable plasma. The material in question is a material for which it is much more difficult to ignite a reliable plasma because it is a more complex target made of different compounds, therefore this target will be affected by grain size, impurities, and other factors from its manufacturing, therefore there are more ignition faults and retries than with other conventional targets using the same recipe settings. It was found that ignition retries and faults can be improved by implementing sequence start cleans, high pressure ignition using the sputter on shield, and/or by using a higher wattage power supply to ignite the plasma with the ion gauge on. Each method was shown to decrease the number of retries and faults and can be used on PVD systems with targets which are difficult to ignite. Any combination of these solutions should result in improvement of up to 50% reduction in ignition faults.

Lattice distortions can stabilize magnetic ground states not observed in the bulk for thin films of undoped cobalt perovskites ACoO 3 . We have found that lattice distortions, in the form of tensile epitaxial strain, can stabilize a ferromagnetic ground state in PrCoO 3 thin films below 65 K. However, in Pr 0.7 Y 0.3 CoO 3 , which has a smaller unit cell, similar levels of tensile strain are insufficient to induce ferromagnetism. These results indicate the importance of A-site cation choice for Co spin-state and Co-O-Co exchange interactions, offering another dimension to tune magnetic order in thin film cobalt perovskites.

© 2017 American Chemical Society. Light-matter interaction at the nanoscale in magnetic materials is a topic of intense research in view of potential applications in next-generation high-density magnetic recording. Laser-assisted switching provides a pathway for overcoming the material constraints of high-anisotropy and high-packing density media, though much about the dynamics of the switching process remains unexplored. We use ultrafast small-angle X-ray scattering at an X-ray free-electron laser to probe the magnetic switching dynamics of FePt nanoparticles embedded in a carbon matrix following excitation by an optical femtosecond laser pulse. We observe that the combination of laser excitation and applied static magnetic field, 1 order of magnitude smaller than the coercive field, can overcome the magnetic anisotropy barrier between "up" and "down" magnetization, enabling magnetization switching. This magnetic switching is found to be inhomogeneous throughout the material with some individual FePt nanoparticles neither switching nor demagnetizing. The origin of this behavior is identified as the near-field modification of the incident laser radiation around FePt nanoparticles. The fraction of not-switching nanoparticles is influenced by the heat flow between FePt and a heat-sink layer.

Magnetostriction, the strain induced by a change in magnetization, is a universal effect in magnetic materials. Owing to the difficulty in unraveling its microscopic origin, it has been largely treated phenomenologically. Here, we show how the source of magnetostriction—the underlying magnetoelastic stress—can be separated in the time domain, opening the door for an atomistic understanding. X-ray and electron diffraction are used to separate the sub-picosecond spin and lattice responses of FePt nanoparticles. Following excitation with a 50-fs laser pulse, time-resolved X-ray diffraction demonstrates that magnetic order is lost within the nanoparticles with a time constant of 146 fs. Ultrafast electron diffraction reveals that this demagnetization is followed by an anisotropic, three-dimensional lattice motion. Analysis of the size, speed, and symmetry of the lattice motion, together with ab initio calculations accounting for the stresses due to electrons and phonons, allow us to reveal the magnetoelastic stress generated by demagnetization., Although magnetostriction is universal in magnetic materials, understanding its microscopic origin remains challenging. Here the authors use X-ray and ultrafast electron diffraction to separate the material’s sub-picosecond spin and lattice responses and reveal the magnetoelastic stress generated by demagnetization.

A new technique for characterizing the thermal properties of heat-assisted magnetic recording media (HAMR) using pulsed near-field heating recording with a static tester is reported. It has the advantage over traditional recording techniques of enabling studies of the 1–100 ns transient thermal configurations rather than only thermal steady states. The technique is applied to HAMR media with different heatsink thicknesses. While each media has a different steady-state temperature profile, the heatsinking differences are eliminated or enhanced by tuning the pulse duration for each media. The technique is used to extract thermal properties of the media.

Physical review letters 121(13), 137403 (2018). doi:10.1103/PhysRevLett.121.137403, Using ultrafast $≃2.5 fs$ and $≃25 fs$ self-amplified spontaneous emission pulses of increasing intensity and a novel experimental scheme, we report the concurrent increase of stimulated emission in the forward direction and loss of out-of-beam diffraction contrast for a $Co/Pd$ multilayer sample. The experimental results are quantitatively accounted for by a statistical description of the pulses in conjunction with the optical Bloch equations. The dependence of the stimulated sample response on the incident intensity, coherence time, and energy jitter of the employed pulses reveals the importance of increased control of x-ray free electron laser radiation., Published by APS, College Park, Md.

“The technical support from SLAC Accelerator Directorate, Technology Innovation Directorate, LCLS laser division and Test Facility Division is gratefully acknowledged. We thank S.P. Weathersby, R.K. Jobe, D. McCormick, A. Mitra, S. Carron and J. Corbett for their invaluable help and technical assistance. Research at SLAC was supported through the SIMES Institute which like the LCLS and SSRL user facilities is funded by the Office of Basic Energy Sciences of the U.S. Department of Energy under Contract No. DE-AC02-76SF00515. The UED work was performed at SLAC MeV-UED, which is supported in part by the DOE BES SUF Division Accelerator & Detector R&D program, the LCLS Facility, and SLAC under contract Nos. DE-AC02-05-CH11231 and DE-AC02-76SF00515. Use of the Linac Coherent Light Source (LCLS), SLAC National Accelerator Laboratory, is supported by the U.S. Department of Energy, Office of Science, Office of Basic Energy Sciences under Contract No. DE-AC02-76SF00515.”and“Work at BNL was supported by DOE BES Materials Science and Engineering Division under Contract No: DE-AC02-98CH10886. J.C. would like to acknowledge the support from National Science Foundation Grant No. 1207252. E.E.F. would like to acknowledge support from the U.S. Department of Energy (DOE), Office of Basic Energy Sciences (BES) under Award No. DE-SC0003678.”This has been corrected in both the PDF and HTML versions of the Article.

We present helicity and field dependent magnetization dynamics of ferromagnetic Co/Pt multilayers, suitable for all-optical helicity-dependent switching. Employing single-shot time-resolved magneto-optical Kerr effect imaging, our study demonstrates an ultra-fast quenching of the magnetization after a single 60 fs laser pulse excitation followed by a recovery. Full demagnetization occurs within 1 ps after laser excitation. The magnetization dynamics reveals a small helicity dependence caused by magnetic circular dichroism. When an external magnetic field is applied, a heat-assisted magnetization reversal occurs on a nanosecond time scale.

We demonstrate that a combination of electronic structure modification and oxygen vacancy ordering can stabilize a long-range ferromagnetic ground state in epitaxial LaCoO_(3) thin films. Highest saturation magnetization values are found in the thin films in tension on SrTiO_(3) and (La,Sr)(Al,Ta)O_(3) substrates and the lowest values are found in thin films in compression on LaAlO_(3). Electron microscopy reveals oxygen vacancy ordering to varying degrees in all samples, although samples with the highest magnetization are the most defective. Element-specific x-ray absorption techniques reveal the presence of high spin Co^(2+) and Co^(3+) as well as low spin Co^(3+) in different proportions depending on the strain state. The interactions among the high spin Co ions and the oxygen vacancy superstructure are correlated with the stabilization of the long-range ferromagnetic order.

The origin of ferromagnetism in strained epitaxial ${\mathrm{LaCoO}}_{3}$ films has been a long-standing mystery. Here, we combine atomically resolved $Z$-contrast imaging, electron-energy-loss spectroscopy, and density-functional calculations to demonstrate that, in epitaxial ${\mathrm{LaCoO}}_{3}$ films, oxygen-vacancy superstructures release strain, control the film's electronic properties, and produce the observed ferromagnetism via the excess electrons in the Co $d$ states. Although oxygen vacancies typically dope a material $n$-type, we find that ordered vacancies induce Peierls-like minigaps which, combined with strain relaxation, trigger a nonlinear rupture of the energy bands, resulting in insulating behavior.

Epitaxial thin films of CaVO{sub 3} were synthesized on SrTiO{sub 3}, LaAlO{sub 3} and (La{sub 0.27}Sr{sub 0.73})(Al{sub 0.65}Ta{sub 0.35})O{sub 3} substrates by pulsed laser deposition. All CaVO{sub 3} films, independent of epitaxial strain, exhibit metallic and Pauli paramagnetic behavior as CaVO{sub 3} single crystals. X-ray absorption measurements confirmed the 4+ valence state for Vanadium ions. With prolonged air exposure, an increasing amount of V{sup 3+} is detected and is attributed to oxygen loss in the near surface region of the films.

We observe interfacial ferromagnetism in superlattices of the paramagnetic metal ${\mathrm{LaNiO}}_{3}$ and the antiferromagnetic insulator ${\mathrm{CaMnO}}_{3}$. ${\mathrm{LaNiO}}_{3}$ exhibits a thickness dependent metal-insulator transition and we find the emergence of ferromagnetism to be coincident with the conducting state of ${\mathrm{LaNiO}}_{3}$. That is, only superlattices in which the ${\mathrm{LaNiO}}_{3}$ layers are metallic exhibit ferromagnetism. Using several magnetic probes, we have determined that the ferromagnetism arises in a single unit cell of ${\mathrm{CaMnO}}_{3}$ at the interface. Together these results suggest that ferromagnetism can be attributed to a double exchange interaction among Mn ions mediated by the adjacent itinerant metal.

We demonstrate the stabilization of a ferrimagnetic ground state in epitaxial films of PrCoO${}_{3}$ grown on SrTiO${}_{3}$ (001) substrates, in stark contrast to paramagnetic behavior observed in bulk. Heteroepitaxial strain is found to induce long-range ordering of the Co ions, which we deduce to be in a high-spin state. The ferromagnetic ordering of the CoO${}_{6}$ array is accompanied by ordering of the Pr sublattice in an antiparallel orientation to the Co. The ordering of the Pr sublattice provides evidence for significant Co-Pr exchange likely facilitated by the presence of high-spin Co.

We have found ferromagnetism in epitaxially grown superlattices of ${\mathrm{CaRuO}}_{3}/{\mathrm{CaMnO}}_{3}$ that arises in one unit cell at the interface. Scanning transmission electron microscopy and electron energy loss spectroscopy indicate that the difference in magnitude of the Mn valence states between the center of the ${\mathrm{CaMnO}}_{3}$ layer and the interface region is consistent with double exchange interaction among the Mn ions at the interface. Polarized neutron reflectivity and the ${\mathrm{CaMnO}}_{3}$ thickness dependence of the exchange bias field together indicate that the interfacial ferromagnetism is only limited to one unit cell of ${\mathrm{CaMnO}}_{3}$ at each interface. The interfacial moment alternates between the $1{\ensuremath{\mu}}_{B}/\mathrm{\text{interface}}$ Mn ion for even ${\mathrm{CaMnO}}_{3}$ layers and the $0.5{\ensuremath{\mu}}_{B}/\mathrm{\text{interface}}$ Mn ion for odd ${\mathrm{CaMnO}}_{3}$ layers. This modulation, combined with the exchange bias, suggests the presence of a modulating interlayer coupling between neighboring ferromagnetic interfaces via the antiferromagnetic ${\mathrm{CaMnO}}_{3}$ layers.

In this work, we present a detailed investigation of FePt-substrate interfaces and their influence towards the microstructural and magnetic configurations of the resulting metallic films. Discontinuous FePt films of roughly 15 nm thickness are deposited at 750 °C on MgO, MgAl2O4, SrTiO3, and (La,Sr)(Al,Ta)O3 single-crystalline substrates. All of these films mainly show out-of-plane textured FePt islands; however, fractions of L12 and in-plane oriented crystals are observed for the films on substrates with reduced lattice mismatch. Reduced easy axis coercivities and enhanced hard axis remanence values affirm this observation. Moreover, quantitative high-resolution transmission electron microscope analysis reveals that the reduced lattice mismatch results in a decreased density of dislocations, especially misfit dislocations, at the FePt-substrate interface. To further extend the research, carbon-doped FePt+32%C films are deposited on single-crystalline and sputtered MgO at 750 °C and 650 °C, respectively, to characterize the influence of a segregating media and reduced grain size. A comparison to the pure FePt sample reveals that the presence of seed layer grain boundaries leads to an increased fraction of in-plane oriented material, while the density of misfit dislocations solely depends on the degree of lattice mismatch.

We have demonstrated that epitaxial films of LaVO${}_{3}$ and LaTiO${}_{3}$ can exhibit metallicity though their bulk counterparts are Mott insulators. When LaTiO${}_{3}$ films are compressively strained on SrTiO${}_{3}$ substrates, we observe metallicity that is attributed largely to epitaxial strain-induced electronic structure modifications and secondarily to interface electronic reconstruction at the LaTiO${}_{3}$/SrTiO${}_{3}$ interface. However, when LaVO${}_{3}$ films are compressively strained on SrTiO${}_{3}$ substrates, the observed metallicity is primarily attributed to interface effects. Signatures of weak localization are observed at low temperature in LaVO${}_{3}$ films in the temperature, film thickness, as well as magnetic field dependence of the magnetoresistance.

Orthorhombic bulk ${\text{LaTiO}}_{3}$ is a correlated Mott insulator whose delicate antiferromagnetic insulating ground state can be easily destroyed by cation vacancies, excess oxygen, or alkaline-earth dopants, resulting in metallicity. Here we show that metallic conduction can also be realized in epitaxial ${\text{LaTiO}}_{3}$ thin films on (001) ${\text{SrTiO}}_{3}$ substrates, while films grown on (110) ${\text{DyScO}}_{3}$ and ${\text{GdScO}}_{3}$ substrates are insulating. These results illustrate the sensitivity of electrical transport to lattice effects and demonstrate the tunability of correlated oxide thin-film properties via substrate-induced deformation.

We analyze the magnetic cluster size (MCS) and magnetic cluster size distribution (MCSD) in a variety of perpendicular magnetic recording (PMR) media designs using resonant small angle x-ray scattering at the Co L3 absorption edge. The different PMR media flavors considered here vary in grain size between 7.5 and 9.5 nm as well as in lateral inter-granular exchange strength, which is controlled via the segregant amount. While for high inter-granular exchange, the MCS increases rapidly for grain sizes below 8.5 nm, we show that for increased amount of segregant with less exchange the MCS remains relatively small, even for grain sizes of 7.5 and 8 nm. However, the MCSD still increases sharply when shrinking grains from 8 to 7.5 nm. We show evidence that recording performance such as signal-to-noise-ratio on the spin stand correlates well with the product of magnetic cluster size and magnetic cluster size distribution.

The steadily increasing amount of digital information necessitates the availability of reliable high capacity magnetic data storage. Here, future hard disk drives with extended areal storage densities beyond 1.0 Tb/in2 are envisioned by using high anisotropy granular and chemically L10-ordered FePt (002) perpendicular media within a heat-assisted magnetic recording scheme. Perpendicular texturing of the [001] easy axes of the individual grains can be achieved by using MgO seed layers. It is therefore investigated, if and how an Ar+ ion irradiation of the MgO seed layer prior to the deposition of the magnetic material influences the MgO surface properties and hereby the FePt [001] texture. Structural investigations reveal a flattening of the seed layer surface accompanied by a change in the morphology of the FePt grains. Moreover, the fraction of small second layer particles and the degree of coalescence of the primarily deposited FePt grains strongly increases. As for the magnetic performance, this results in a reduced coercivity along the magnetic easy axis (out of plane) and in enhanced hard axis (in-plane) remanence values. The irradiation induced changes in the magnetic properties of the granular FePt-C films are traced back to the accordingly modified atomic structure of the FePt-MgO interface region.

We analyze the magnetic design for different generations of perpendicular magnetic recording (PMR) media using resonant soft x-ray small angle x-ray scattering. This technique allows us to simultaneously extract in a single experiment the key structural and magnetic parameters, i.e., lateral structural grain and magnetic cluster sizes as well as their distributions. We find that earlier PMR media generations relied on an initial reduction in the magnetic cluster size down to the grain level of the high anisotropy granular base layer, while very recent media designs introduce more exchange decoupling also within the softer laterally continuous cap layer. We highlight that this recent development allows optimizing magnetic cluster size and magnetic cluster size distribution within the composite media system for maximum achievable area density, while keeping the structural grain size roughly constant.

Nanocrystalline (NC) textured Mn0.5Zn0.6Fe1.9O4 (MZFO) films, grown at room temperature on both isostructural and non-isostructural substrates, show magnetization values significantly suppressed from epitaxial MZFO films. X-ray absorption spectroscopy and x-ray magnetic circular dichroism measurements indicate larger ratios of Fe3+ to Fe2+ ions on the tetrahedral sites in the NC films compared to the epitaxial films. The magnetization loops of the NC films are shifted by 200−400 Oe at low temperatures. No such effect is observed in the epitaxial films. We hypothesize that the presence of a more structurally disordered, possibly magnetically frustrated, matrix exchange biases the crystalline regions.

We have studied epitaxially grown superlattices of CaRuO3/CaMnO3 as well as an alloy film of CaMn0.5Ru0.5O3 on (001) SrTiO3 substrates. In contrast to previous experiments, we have studied CRO/CMO superlattices with a constant CRO thickness and variable CMO thickness. All superlattices exhibit Curie temperatures (TC) of 110 K. The saturated magnetization per interfacial Mn cation has been found to be 1.1 μB/Mn ion. The TC’s of the superlattices are much lower than the TC of the alloy film while the saturated magnetization values are larger than that of the alloy film. These observations suggest that interdiffusion alone cannot account for ferromagnetism in the superlattices and that double exchange induced FM must play a role at the interfaces.

Epitaxial LaCoO3 films were synthesized on LaAlO3 substrates to explore the role of epitaxial strain and structure on the ferromagnetism observed in these biaxially compressed films. Coherent strain and tetragonal structure were only achieved in thin film samples grown using higher energy densities. The strain relaxed with increasing thickness and was accompanied by increasing mosaic spread. Higher magnetization values were consistently seen in fully relaxed films grown using lower laser energy density. These results suggest that epitaxial strain is not the only factor determining the ferromagnetism and that the microstructure and defects may play a significant role.

Thin films of epitaxial LaCoO{sub 3} were synthesized on SrTiO{sub 3} and (La, Sr)(Al, Ta)O{sub 3} substrates varying the oxygen background pressure in order to evaluate the impact of epitaxial growth as well as oxygen vacancies on the long range magnetic order. The epitaxial constraints from the substrate impose a tetragonal distortion compared to the bulk form. X-ray absorption and x-ray magnetic circular dichroism measurements confirmed that the ferromagnetism arises from the Co ions and persists through the entire thickness of the film. It was found that for the thin films to show ferromagnetic order they have to be grown under the higher oxygen pressures, since a decrease in oxygen deposition pressure alters the film structure and suppresses ferromagnetism in the LaCoO{sub 3} films. A correlation of the structure and magnetism suggests that the tetragonal distortions induce the ferromagnetism.