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Electric field control of the exchange bias effect across ferromagnet/antiferromagnet (FM/AF) interfaces has offered exciting potentials for low-energy-dissipation spintronics. In particular, the solid state magneto-ionic means is highly appealing as it may allow reconfigurable electronics by transforming the all-important FM/AF interfaces through ionic migration. In this work, we demonstrate an approach that combines the chemically induced magneto-ionic effect with the electric field driving of nitrogen in the Ta/Co$_{0.7}$Fe$_{0.3}$/MnN/Ta structure to electrically manipulate exchange bias. Upon field-cooling the heterostructure, ionic diffusion of nitrogen from MnN into the Ta layers occurs. A significant exchange bias of 618 Oe at 300 K and 1484 Oe at 10 K is observed, which can be further enhanced after a voltage conditioning by 5% and 19%, respectively. This enhancement can be reversed by voltage conditioning with an opposite polarity. Nitrogen migration within the MnN layer and into the Ta capping layer cause the enhancement in exchange bias, which is observed in polarized neutron reflectometry studies. These results demonstrate an effective nitrogen-ion based magneto-ionic manipulation of exchange bias in solid-state devices., 28 pages, 4 figures; supporting information: 17 pages, 11 figures

Neuroimaging of certain pathologies requires both multi-parametric qualitative and quantitative imaging. The role of the quantitative MRI (qMRI) is well accepted but suffers from long acquisition times leading to patient discomfort, especially in geriatric and pediatric patients. Previous studies show that synthetic MRI can be used in order to reduce the scan time and provide qMRI as well as multi-contrast data. However, this approach suffers from artifacts such as partial volume and flow. In order to increase the scan efficiency (the number of contrasts and quantitative maps acquired per unit time), we designed, simulated, and demonstrated rapid, simultaneous, multi-contrast qualitative (T1 weighted, T1 fluid attenuated inversion recovery (FLAIR), T2 weighted, water, and fat), and quantitative imaging (T1 and T2 maps) through the approach of tailored MR fingerprinting (TMRF) to cover whole-brain in approximately four minutes.We performed TMRF on in vivo four healthy human brains and in vitro ISMRM/NIST phantom and compared with vendor supplied gold standard (GS) and MRF sequences. All scans were performed on a 3T GE Premier system and images were reconstructed offline using MATLAB. The reconstructed qualitative images were then subjected to custom DL denoising and gradient anisotropic diffusion denoising. The quantitative tissue parametric maps were reconstructed using a dense neural network to gain computational speed compared to dictionary matching. The grey matter and white matter tissues in qualitative and quantitative data for the in vivo datasets were segmented semi-automatically. The SNR and mean contrasts were plotted and compared across all three methods. The GS images show better SNR in all four subjects compared to MRF and TMRF (GS>TMRF>MRF). The T1 and T2 values of MRF are relatively overestimated as compared to GS and TMRF. The scan efficiency for TMRF is 1.72 min-1 which is higher compared to GS (0.32 min-1) and MRF (0.90 min-1).

Standardized magnetic resonance imaging (MRI) protocols are important for the diagnosis and monitoring of patients with multiple sclerosis (MS). The Consortium of Multiple Sclerosis Centers (CMSC) convened an international panel of MRI experts to review and update the current guidelines. The objective was to update the standardized MRI protocol and clinical guidelines for diagnosis and follow-up of MS and develop strategies for advocacy, dissemination, and implementation. Conference attendees included neurologists, radiologists, technologists, and imaging scientists with expertise in MS. Representatives from the CMSC, Magnetic Resonance Imaging in MS (MAGNIMS), North American Imaging in Multiple Sclerosis Cooperative, US Department of Veteran Affairs, National Multiple Sclerosis Society, Multiple Sclerosis Association of America, MRI manufacturers, and commercial image analysis companies were present. Before the meeting, CMSC members were surveyed about standardized MRI protocols, gadolinium use, need for diffusion-weighted imaging, and the central vein sign. The panel worked to make the CMSC and MAGNIMS MRI protocols similar so that the updated guidelines could ultimately be accepted by international consensus. Advocacy efforts will promote the importance of standardized MS MRI protocols. Dissemination will include publications, meeting abstracts, educational programming, webinars, “meet the expert” teleconferences, and examination cards. Implementation will require comprehensive and coordinated efforts to make the protocol easy to access and use. The ultimate vision, and goal, is for the guidelines to be universally useful, usable, and used as the standard of care for patients with MS.

The intrinsic magnetic topological insulator MnBi2Te4 (MBT) has provided a platform for the successful realization of exotic quantum phenomena. To broaden the horizons of MBT-based material systems, we intercalate ferromagnetic MnTe layers to construct the [(MBT)(MnTe)m]N superlattices by molecular beam epitaxy. The effective incorporation of ferromagnetic spacers mediates the anti-ferromagnetic interlayer coupling among the MBT layers through the exchange spring effect at the MBT/MnTe hetero-interfaces. Moreover, the precise control of the MnTe thickness enables the modulation of relative strengths among the constituent magnetic orders, leading to tunable magnetoelectric responses, while the superlattice periodicity serves as an additional tuning parameter to tailor the spin configurations of the synthesized multi-layers. Our results demonstrate the advantages of superlattice engineering for optimizing the magnetic interactions in MBT-family systems, and the ferromagnet-intercalated strategy opens up new avenues in magnetic topological insulator structural design and spintronic applications., 20 pages, 5 figures

Cobalt oxides have long been understood to display intriguing phenomena known as spin-state crossovers, where the cobalt ion spin changes vs. temperature, pressure, etc. A very different situation was recently uncovered in praseodymium-containing cobalt oxides, where a first-order coupled spin-state/structural/metal-insulator transition occurs, driven by a remarkable praseodymium valence transition. Such valence transitions, particularly when triggering spin-state and metal-insulator transitions, offer highly appealing functionality, but have thus far been confined to cryogenic temperatures in bulk materials (e.g., 90 K in Pr1-xCaxCoO3). Here, we show that in thin films of the complex perovskite (Pr1-yYy)1-xCaxCoO3-{\delta}, heteroepitaxial strain tuning enables stabilization of valence-driven spin-state/structural/metal-insulator transitions to at least 291 K, i.e., around room temperature. The technological implications of this result are accompanied by fundamental prospects, as complete strain control of the electronic ground state is demonstrated, from ferromagnetic metal under tension to nonmagnetic insulator under compression, thereby exposing a potential novel quantum critical point., Comment: 35 pages, 7 figures

Nonmagnetic heavy metals can develop a magnetic moment due to the proximity of a magnetic layer. Here, the sign of the proximity effect in Pt and W grown on the ferrimagnetic insulator Dy${}_{3}$Fe${}_{5}$O${}_{12}$ (DyIG) is examined. Polarized neutron reflectometry indicates the importance of a clean metal/garnet interface, and shows that the proximity effect in Pt/DyIG is positive above and below the DyIG compensation temperature, indicating a different origin compared to that of Pt adjacent to a ferrimagnetic metal alloy.

Purpose Assess feasibility of ultrashort echo time (UTE) T2* cartilage mapping in sacroiliac (SI) joints. Methods Prospective magnetic resonance imagings with UTE T2* cartilage maps obtained on 20 SI joints in 10 subjects. Each joint was segmented into thirds by 2 radiologists. The UTE T2* maps were analyzed; reliability and differences in UTE T2* values between radiologists were assessed. Results Mean UTE T2* value was 10.44 ± 0.60 ms. No difference between right/left SI joints (median, 10.52 vs 10.45 ms; P = 0.940), men/women (median, 10.34 vs. 10.57 ms; P = 0.174), or different anatomic regions (median range 10.55-10.69 ms; P = 0.805). Intraclass correlation coefficients were 0.94 to 0.99 (intraobserver) and 0.91 to 0.96 (interobserver). Mean bias ± standard deviation on Bland-Altman was -0.137 ± 0.196 ms (limits of agreement -0.521 and 0.247) without proportional bias (β = 0.148, P = 0.534). Conclusions The UTE T2* cartilage mapping in the SI joints is feasible with high reader reliability.

Background Ultrashort echo time (UTE) T2* is sensitive to molecular changes within the deep calcified layer of cartilage. Feasibility of its use in the hip needs to be established to determine suitability for clinical use. Purpose To establish feasibility of UTE T2* cartilage mapping in the hip and determine if differences in regional values exist. Material and Methods MRI scans with UTE T2* cartilage maps were prospectively acquired on eight hips. Hip cartilage was segmented into whole and deep layers in anterosuperior, superior, and posterosuperior regions. Quantitative UTE T2* maps were analyzed (independent one-way ANOVA) and reliability was calculated (ICC). Results UTE T2* mean values (anterosuperior, superior, posterosuperior): full femoral layer (19.55, 18.43, 16.84 ms) ( P=0.004), full acetabular layer (19.37, 17.50, 16.73 ms) ( P=0.013), deep femoral layer (18.68, 17.90, 15.74 ms) ( P=0.010), and deep acetabular layer (17.81, 16.18, 15.31 ms) ( P=0.007). Values were higher in anterosuperior compared to posterosuperior regions (mean difference; 95% confidence interval [CI]): full femur layer (2.71 ms; 95% CI 0.91–4.51: P=0.003), deep femur layer (2.94 ms; 95% CI 0.69–5.19; P=0.009), full acetabular layer (2.63 ms 95% CI 0.55–4.72; P=0.012), and deep acetabular layer (2.50 ms; 95% CI 0.69–4.30; P=0.006). Intra-reader (ICC 0.89–0.99) and inter-reader reliability (ICC 0.63–0.96) were good to excellent for the majority of cartilage layers. Conclusion UTE T2* cartilage mapping was feasible in the hip with mean values in the range of 16.84–19.55 ms in the femur and 16.73–19.37 ms in the acetabulum. Significantly higher values were present in the anterosuperior region compared to the posterosuperior region.

We report spin-to-charge and charge-to-spin conversion at room temperature in heterostructure devices that interface an archetypal Dirac semimetal, Cd3As2, with a metallic ferromagnet, Ni0.80Fe0.20 (permalloy). The spin-charge interconversion is detected by both spin torque ferromagnetic resonance and ferromagnetic resonance driven spin pumping. Analysis of the symmetric and anti-symmetric components of the mixing voltage in spin torque ferromagnetic resonance and the frequency and power dependence of the spin pumping signal show that the behavior of these processes is consistent with previously reported spin-charge interconversion mechanisms in heavy metals, topological insulators, and Weyl semimetals. We find that the efficiency of spin-charge interconversion in Cd3As2/permalloy bilayers can be comparable to that in heavy metals. We discuss the underlying mechanisms by comparing our results with first principles calculations.

While being electrically insulating, magnetic insulators can behave as good spin conductors by carrying spin current with excited spin waves. So far, magnetic insulators are utilized in multilayer heterostructures for optimizing spin transport or to form magnon spin valves for reaching controls over the spin flow. In these studies, it remains an intensively visited topic as to what the corresponding roles of coherent and incoherent magnons are in the spin transmission. Meanwhile, understanding the underlying mechanism associated with spin transmission in insulators can help to identify new mechanisms that can further improve the spin transport efficiency. Here, by studying spin transport in a magnetic-metal/magnetic-insulator/platinum multilayer, it is demonstrated that coherent magnons can transfer spins efficiently above the magnon bandgap of magnetic insulators. Particularly the standing spin-wave mode can greatly enhance the spin flow by inducing a resonant magnon transmission. Furthermore, within the magnon bandgap, a shutdown of spin transmission due to the blocking of coherent magnons is observed. The demonstrated magnon transmission enhancement and filtering effect provides an efficient method for modulating spin current in magnonic devices.

High spin-orbit torques (SOTs) generated by topological materials and heavy metals interfaced with a ferromagnetic layer show promise for next generation magnetic memory and logic devices. SOTs generated from the in-plane spin polarization along y-axis originated by the spin Hall and Edelstein effects can switch magnetization collinear with the spin polarization in the absence of external magnetic fields. However, an external magnetic field is required to switch the magnetization along x and z-axes via SOT generated by y-spin polarization. Here, we present that the above limitation can be circumvented by unconventional SOT in magnetron-sputtered thin film MnPd3. In addition to the conventional in-plane anti-damping-like torque due to the y-spin polarization, out-of-plane and in-plane anti-damping-like torques originating from z-spin and x-spin polarizations, respectively have been observed at room temperature. The spin torque efficiency (θ_y) corresponding to the y-spin polarization from MnPd3 thin films grown on thermally oxidized silicon substrate and post annealed at 400 ℃ is 0.34 - 0.44 while the spin conductivity (σ_zx^y) is ~ 5.70 – 7.30× 105 ℏ⁄2e Ω-1m-1. Remarkably, we have demonstrated complete external magnetic field-free switching of perpendicular Co layer via unconventional out-of-plane anti-damping-like torque from z-spin polarization. Based on the density functional theory calculations, we determine that the observed x- and z- spin polarizations with the in-plane charge current are due to the low symmetry of the (114) oriented MnPd3 thin films. Taken together, the new material reported here provides a path to realize a practical spin channel in ultrafast magnetic memory and logic devices.

Standardized magnetic resonance imaging (MRI) protocols are important for the diagnosis and monitoring of patients with multiple sclerosis (MS). The Consortium of Multiple Sclerosis Centers (CMSC) convened an international panel of MRI experts to review and update the current guidelines. The objective was to update the standardized MRI protocol and clinical guidelines for diagnosis and follow-up of MS and develop strategies for advocacy, dissemination, and implementation. Conference attendees included neurologists, radiologists, technologists, and imaging scientists with expertise in MS. Representatives from the CMSC, Magnetic Resonance Imaging in MS (MAGNIMS), North American Imaging in Multiple Sclerosis Cooperative, US Department of Veteran Affairs, National Multiple Sclerosis Society, Multiple Sclerosis Association of America, MRI manufacturers, and commercial image analysis companies were present. Before the meeting, CMSC members were surveyed about standardized MRI protocols, gadolinium use, need for diffusion-weighted imaging, and the central vein sign. The panel worked to make the CMSC and MAGNIMS MRI protocols similar so that the updated guidelines could ultimately be accepted by international consensus. Advocacy efforts will promote the importance of standardized MS MRI protocols. Dissemination will include publications, meeting abstracts, educational programming, webinars, “meet the expert” teleconferences, and examination cards. Implementation will require comprehensive and coordinated efforts to make the protocol easy to access and use. The ultimate vision, and goal, is for the guidelines to be universally useful, usable, and used as the standard of care for patients with MS.

Tuning the Dzyaloshinskii-Moriya interaction (DMI) using electric (E)-fields in magnetic devices has opened up new perspectives for controlling the stabilization of chiral spin structures. Recent efforts have used voltage-induced charge redistribution at magnetic/oxides interfaces to modulate the DMI. This approach is attractive for active devices but tends to be volatile, making it energy-demanding. Here we demonstrate nonvolatile E-field manipulation of the DMI by ionic-liquid gating of Pt/Co/HfO2 ultra thin films. The E-field effect on the DMI is linked to the migration of oxygen species from the HfO2 layer into the Co and Pt layers and subsequent anchoring. This effect permanently changes the properties of the material, showing that E-fields can be used not only for local gating in devices but also as a material design tool for post growth tuning of the DMI.

The intersection of topology and magnetism represents a new playground to discover novel quantum phenomena and device concepts. In this work, we show that under certain synthetic conditions, a van der Waals single-crystalline compound $\mathrm{MnS}{\mathrm{b}}_{1.8}\mathrm{B}{\mathrm{i}}_{0.2}\mathrm{T}{\mathrm{e}}_{4}$ exhibits a net ferromagnetic state with a Curie temperature of 26 K, in contrast to the fully compensated antiferromagnetic order observed previously for other members of the $\mathrm{Mn}{(\mathrm{Sb},\mathrm{Bi})}_{2}\mathrm{T}{\mathrm{e}}_{4}$ family. We employ magneto-transport, bulk magnetization, x-ray and neutron scattering studies to illustrate the structural, magnetic, and electrical properties of $\mathrm{MnS}{\mathrm{b}}_{1.8}\mathrm{B}{\mathrm{i}}_{0.2}\mathrm{T}{\mathrm{e}}_{4}$. Our structural analyses reveal considerable Mn-Sb site mixing and suggest a recently proposed mechanism, where Mn occupying the Sb site mediates a ferromagnetic coupling between Mn layers [Murakami et al., Phys. Rev. B 100, 195103 (2019)], could be at play. Close comparisons made to an antiferromagnetic compound $\mathrm{MnS}{\mathrm{b}}_{2}\mathrm{T}{\mathrm{e}}_{4}$ illustrate the subtle magnetic interactions of the system and the important role played by local chemistry. The appearance of an unusual anomalous Hall effect in $\mathrm{MnS}{\mathrm{b}}_{1.8}\mathrm{B}{\mathrm{i}}_{0.2}\mathrm{T}{\mathrm{e}}_{4}$ at low temperatures hints at a magnetic ground state different from other members of this family. Our results are an important step in the synthesis and understanding of magnetism in materials with topological characteristics.

Superconducting ($S$) thin film superlattices composed of Nb and a normal metal spacer ($N$) have been extensively utilized in Josephson junctions given their favorable surface roughness compared to Nb films of comparable thickness. In this work, we characterize the London penetration depth and Ginzburg-Landau coherence lengths of $S/N$ superlattices using polarized neutron reflectometry and electrical transport. Despite the normal metal spacer layers being only approximately 8% of the total superlattice thickness, we surprisingly find that the introduction of these thin $N$ spacers between $S$ layers leads to a dramatic increase in the measured London penetration depth compared to that of a single Nb film of comparable thickness. Using the measured values for the effective in- and out-of-plane coherence lengths, we quantify the induced anisotropy of the superlattice samples and compare to a single Nb film sample. From these results, we find that that the superlattices behave similarly to layered 2D superconductors., Comment: 9 pages, 3 figures main text and 7 pages, 5 figures supplemental materials

Development of novel magnetic materials is of interest for fundamental studies and applications such as spintronics, permanent magnetics, and sensors. We report on the first experimental realization of single element ferromagnetism, since Fe, Co, and Ni, in metastable tetragonal Ru, which has been predicted. Body-centered tetragonal Ru phase is realized by use of strain via seed layer engineering. X-ray diffraction and electron microscopy confirm the epitaxial mechanism to obtain tetragonal phase Ru. We observed a saturation magnetization of 148 and 160 emu cm−3 at room temperature and 10 K, respectively. Control samples ensure the ferromagnetism we report on is from tetragonal Ru and not from magnetic contamination. The effect of thickness on the magnetic properties is also studied, and it is observed that increasing thickness results in strain relaxation, and thus diluting the magnetization. Anomalous Hall measurements are used to confirm its ferromagnetic behavior., Until now, there have been three choices for a room temperature (RT) single element ferromagnetic material in fundamental studies and applications. Here the authors achieved body-centered tetragonal phase ruthenium thin films by epitaxial growth, which is the 4th RT ferromagnetic single element material.

International audience; The possibility to tune the Dzyaloshinskii Moriya interaction (DMI) by electric (E) field gating in ultra-thin magnetic materials has opened new perspectives in terms of controlling the stabilization of chiral spin structures. Most recent efforts have used voltage-induced charge redistribution at the interface between a metal and an oxide to modulate DMI. This approach is attractive for active devices but it tends to be volatile, making it energy demanding, and it is limited by Coulomb screening in the metal. Here we have demonstrated the non-volatile E-field manipulation of DMI by ionic liquid gating of Pt/Co/HfO2 ultra-thin films. The E-field effect on DMI scales with the E-field exposure time and is proposed to be linked to the migration and subsequent anchoring of oxygen species from the HfO2 layer into the Co and Pt layers. This effect permanently changes the properties of the material showing that E-fields can not only be used for local gating in devices but also as a highly scalable materials design tool for post-growth tuning of DMI.

This paper shows a spin fluctuation-driven spin scattering and a metastable canted antiferromagnetic phase in MnBi${}_{2}$Te${}_{4}$. These are signatures of an intrinsic anomalous Quantum Hall effect and open up new avenues to realize a quantum anomalous Hall insulator at high temperatures

We report the effects of nitrogen diffusion on exchange bias in MnN/CoFeB heterostructures as a function of MnN thickness and field-annealing temperature. We find that competing effects occur in which high-temperature annealing enhances exchange bias in heterostructures with thick MnN through improved crystallinity, but in thinner samples this annealing ultimately eliminates the exchange bias due to nitrogen deficiency. Using polarized neutron reflectometry and magnetic x-ray spectroscopy, we directly observe increasing amounts of nitrogen migration from MnN into the underlying Ta seed layer with increased annealing temperature. In heterostructures with thin MnN layers, the resulting nitrogen deficiency becomes significant enough to alter the antiferromagnetic state before the Ta seed layer is nitrogen saturated. Furthermore, we observe intermixing at the MnN/CoFeB interface which is attributed to the nitrogen deficiency creating vacancies in the MnN layer after annealing in a field. This intermixing of Mn with Co and Fe is not believed to be the cause for loss of exchange bias when the MnN layer is too thin but is instead a secondary effect due to increased vacancies after nitrogen migration.

The embedded mask patterning (EMP) process provides a potential L10-FePt media solution for 1–10 Tbit/in2 magnetic recording areal density level. Methanol/Ar reactive ion etch process of FePt media (Ru 2 nm/FePt 8 nm) in EMP is investigated using an ion-neutral-redep synergy etch rate model with the consideration of sputtered redeposition. It has been found that etching of high aspect ratio features spacing that is largely limited by its low etch rate due to high redeposition rate; etching of small size grains is mostly limited by hard mask erosion through the etching process. This would cause etch non-uniformity within the grain size and grain spacing distribution. The hard mask on top of the small size grains (i.e., less than 3 nm) erodes much faster than the larger size gains, resulting in a completely consumed mask before the underlying layers are reached. It is important to reduce local ion sputtering in order to minimize mask erosion for the small grains. We have found that a higher chemical etch selectivity (>30:1) is essential to minimize mask erosion on the grains of 2 nm or larger. We also report that when sputter yield of Ru mask and FePt is adjusted from $10^{-1}$ to $10^{-2}$ level, further improvement is observed with the patterned grain size down to 2.5 nm and spacing down to 1.5 nm, and we suggest that the use of etch gas chemistry with a lighter atomic weight (such as He instead of Ar) would allow for sub-10 nm grain patterning.

Recently, two-dimensional (2D) materials have attracted considerable interest for use in spintronic applications, especially hexagonal close-packed (hcp)-phase boron nitride (BN) as a tunnel barrier. In this paper, we experimentally investigated the structural properties of a sputtered hcp-BN thin film. By optimizing the experimental conditions, we obtained the stoichiometric BN thin film with a ratio of 1:1 of the Ar/N2 sputtering gas. Then the Co/BN/Co magnetic tunnel junction (MTJ) stacks were prepared to study the crystalline structure of the BN tunnel barrier and their epitaxial relationship. We found that the as-deposited BN tunnel barrier layer follows the texture of the bottom Co layer and forms a polycrystalline structure. After the high-temperature treatment of the MTJ stack, texturing of the BN tunnel barrier layer is observed, however, this annealing process makes the BN tunnel barrier noncontinuous and induces serious interdiffusion between layers. These results will open the door for development of spintronic devices based on MTJs with hcp-phase BN tunnel barrier and hcp-phase perpendicular magnetic anisotropy ferromagnetic layer.

Thanks to its unique symmetry, the unidirectional spin Hall and Rashba-Edelstein magnetoresistance (USRMR) is of great fundamental and practical interest, particularly in the context of reading magnetization states in two-terminal spin-orbit torque switching memory and logic devices. Recent studies show that topological insulators could improve USRMR amplitude. However, the topological insulator device configurations studied so far in this context, namely ferromagnetic metal/topological insulator bilayers and magnetically doped topological insulators, suffer from current shunting by the metallic layer and low Curie temperature, respectively. Here, we report large USRMR in a new material category - magnetic insulator/topological insulator bi-layered heterostructures. Such structures exhibit USRMR that is about an order of magnitude larger than the highest values reported so far in all-metal Ta/Co bilayers. We also demonstrate current-induced magnetization switching aided by an Oersted field, and electrical read out by the USRMR, as a prototype memory device.

Embedded Mask Patterning (EMP) method uses a plasma etching process to form ultra-small but thermally stable isolated L10-FePt magnetic grains with embedded Ru hardmask1,2. It has been demonstrated as a promising and highly cost effective solution to fabricate the ultra-high density magnetic media for the next generation hard-disk drive technology, such as heat-assisted magnetic recording (HAMR). EMP process can produce recording media with extremely small and tunable grain size with narrow grain boundary thickness1. For example, at 10 Tbit/in2 recording density the required aspect ratio of vertically etched L1 0 -FePt bit is estimated as high as 4:1 with bit diameter ∼4–5nm and grain boundary ∼2–3nm. In this simulation study, we investigated manufacturability of formation of these nanometer size features in a CH 3 OH/Ar plasma etch process which is used to etch FePt through narrow Ru mask opening and to form volatile Fe-carbonyl product. With addition of Ar gas the etch selectivity of hard mask and magnetic material can be significantly improved3. In order to account for re-deposition of etch product, based on the ion-neutral synergy model4,5,6 we have formed a new chemical-physical etch rate model that also includes the effect of re-deposited etch product by calculating the re-deposition flux distribution in addition to neutral and ion flux coverage over the etch surface. Our simulation shows that the re-deposition rate can increase as etch progresses deeper into the substrate. It significantly reduces the etch rate more inside the higher aspect ratio (AR) features and produces non-uniform etched patterns across the grain boundary distribution, which may degrade media magnetic properties. The etch rate model is combined with a developed 2-D level set computational program to track the moving etch front at different etch time interval with the real-time etch rate distribution calculation. As the result, the simulation allow us to gain insights into the etch process characteristics and to help find optimal etch parameters using the EMP process to fabricate high density recording media.

We studied the tunnel magnetoresistance (TMR) of L10-FePd perpendicular magnetic tunnel junctions (p-MTJs) with an FePd free layer and an inserted diffusion barrier. The diffusion barriers studied here (Ta and W) were shown to enhance the TMR ratio of the p-MTJs formed using high-temperature annealing, which are necessary for the formation of high quality L10-FePd films and MgO barriers. The L10-FePd p-MTJ stack was developed with an FePd free layer with a stack of FePd/X/Co20Fe60B20, where X is the diffusion barrier, and patterned into micron-sized MTJ pillars. The addition of the diffusion barrier was found to greatly enhance the magneto-transport behavior of the L10-FePd p-MTJ pillars such that those without a diffusion barrier exhibited negligible TMR ratios (

We report on the effect of varied capping layers on the formation of thin film MnBi, and the associated magnetic and crystalline properties for use in magnetic memory. MnBi thin films with a capping layer of either Ta, SiO2, Cr, or Au were grown, and it was observed that the magnetic properties vary significantly depending on the capping layer. Continuous 20 nm MnBi thin films capped with Ta and SiO2 show ferromagnetism with large perpendicular magnetocrystalline anisotropy, however, films capped with Cr and Au show no ferromagnetic behavior. In this work, MnBi thin films have been characterized utilizing magnetization vs. field, x-ray diffraction, cross-section transmission electron microscopy, and optical microscopy. We show that the capping layer plays a significant role in the formation of the low temperature phase MnBi structure and propose that the underlying cause is due to a surface energy difference for the MnBi//Au and MnBi//Cr interface, which allows for Mn oxidation, and prevents the formation...

We report the demonstration of picosecond Fresnel imaging with an ultrafast transmission electron microscope (UEM). By operating with a low instrument repetition rate (5 kHz) and without objective-lens excitation, the picosecond demagnetization of an FePt film, via in situ, femtosecond laser excitation, is directly imaged. The dynamics are quantified and monitored as a time-dependent change in the degree of electron coherence within the magnetic domain walls. The relative coherence of conventional (thermionic) Fresnel transmission electron microscopy is also directly compared to that of Fresnel UEM through the domain-wall size. Further, the robustness and reversibility of the domain-wall dynamics are illustrated by repeating the picosecond image scans at defocus values having the same magnitude but different signs (e.g., +25 mm vs. −25 mm). Control experiments and approaches to identifying and isolating systematic errors and sources of artifacts are also described. This work, and continued future developm...

Plasma etching process of single-crystal L10-FePt media [H. Wang et al., Appl. Phys. Lett. 102(5) (2013)] is studied using molecular dynamic simulation. Embedded-Atom Method [M. S. Daw and M. I. Baskes, Phy. Rev. B 29, 6443 (1984); X. W. Zhou, R. A. Johnson and H. N. G. Wadley, Phy. Rev. B 69, 144113 (2004)] is used to calculate the interatomic potential within atoms in FePt alloy, and ZBL potential [J.F. Ziegler, J. P. Biersack and U. Littmark, “The Stopping and Range of Ions in Matter,” Volume 1, Pergamon,1985] in comparison with conventional Lennard-Jones “12-6” potential is applied to interactions between etching gas ions and metal atoms. It is shown the post-etch structure defects can include amorphized surface layer and lattice interstitial point defects that caused by etchant ions passed through the surface layer. We show that the amorphized or damaged FePt lattice surface layer (or “magnetic dead-layer”) thickness after etching increases with ion energy for Ar ion impacts, but significantly small for He ions at up to 250eV ion energy. However, we showed that He sputtering creates more interstitial defects at lower energy levels and defects are deeper below the surface compared to Ar sputtering. We also calculate the interstitial defect level and depth as dependence on ion energy for both Ar and He ions. Media magnetic property loss due to these defects is also discussed.

The 9Be(28Mg,27Na) one-proton removal reaction with a large proton separation energy of Sp(28Mg)=16.79 MeV is studied at intermediate beam energy. Coincidences of the bound 27Na residues with protons and other light charged particles are measured. These data are analyzed to determine the percentage contributions to the proton removal cross section from the elastic and inelastic nucleon removal mechanisms. These deduced contributions are compared with the eikonal reaction model predictions and with the previously measured data for reactions involving the re- moval of more weakly-bound protons from lighter nuclei. The role of transitions of the proton between different bound single-particle configurations upon the elastic breakup cross section is also quantified in this well-bound case. The measured and calculated elastic breakup fractions are found to be in good agreement., Comment: Phys. Rev. C 2014 (accepted)

We have measured spin-triplet supercurrent in Josephson junctions of the form S/F'/F/F'/S, where S is superconducting Nb, F' is a thin Ni layer with in-plane magnetization, and F is a Ni/[Co/Ni]n multilayer with out-of-plane magnetization. The supercurrent in these junctions decays very slowly with F-layer thickness, and is much larger than in similar junctions not containing the two F' layers. Those two features are the characteristic signatures of spin-triplet supercurrent, which is maximized by the orthogonality of the magnetizations in the F and F' layers. Magnetic measurements confirm the out-of-plane anisotropy of the Co/Ni multilayers. These samples have their critical current optimized in the as-prepared state, which will be useful for future applications., 4 pages, 4 figures, formatted in RevTeX version 4. Submitted to Physical Review B on August 13th, 2012

We report final-state-exclusive measurements of the light charged fragments in coincidence with 26Ne residual nuclei following the direct two-proton removal from a neutron-rich 28Mg secondary beam. A Dalitz-plot analysis and comparisons with simulations show that a majority of the triple- coincidence events with two protons display phase-space correlations consistent with the (two-body) kinematics of a spatially-correlated pair-removal mechanism. The fraction of such correlated events, 56(12) %, is consistent with the fraction of the calculated cross section, 64 %, arising from spin S = 0 two-proton configurations in the entrance-channel (shell-model) 28Mg ground state wave function. This result promises access to an additional and more specific probe of the spin and spatial correlations of valence nucleon pairs in exotic nuclei produced as fast secondary beams., Comment: accepted for publication in Physical Review Letters

An unexplained surface anisotropy effect was observed and confirmed in the magnetization reversal process of both L10 phase FePt nanoparticles with octahedral shape and (001) textured L10 FePt thin films with island nanostructures. We suggest that the nature of the observed surface effect is caused by broken symmetry on the FePt surface, which results in weakened exchange coupling for surface atoms. Furthermore, we propose, and experimentally demonstrate, a method to repair the broken symmetry by capping the FePt islands with a Pt layer, which could prove invaluable in understanding fundamental limitations of magnetic nanostructures.

A nanopatterning process, named as the embedded mask patterning, was proposed and experimentally demonstrated based on the FePt recording media. A granular mask layer was deposited on top of a FePt continuous film. The granular pattern of the mask was then transferred down to FePt layer using reactive ion etching. Since controlling magnetic properties is separated from controlling granular nanostructure, FePt grains can be reduced by optimizing the mask layer and patterning process only. This process is also potentially compatible to any state-of-art vacuum process for other electronic devices wafers and heterostructured nanoparticles manufacturing.