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Magnetic Characterization and Tuning of a Mini-Gap In-Vacuum Undulator X25 for NSLS-II
Designed and built by ADC USA Inc. a Mini-Gap In-Vacuum Undulator (MGU X25) has been employed for almost 10 years at NSLS in the Macromolecular Crystallography X25 beamline [1]. The device is a useful and almost readily available X-ray source for NLSL-II beamline, therefore it was extracted in early 2014 from the NSLS X-ray ring after its decommissioning. The Micro-diffraction beamline (NYX) at NSLS-II will utilize the X25-MGU as a bright and tunable X-ray source over the photon range of 5- 20 KeV in the short cell 19-ID. However, the NSLS-II electron beam properties are significantly different from the NSLS ones and the field integral requirements to be met by NSLS-II IDs are more stringent. Consequently, the device was brought to the NSLS-II ID lab for magnetic tuning. It is also a unique opportunity to characterize the magnetic performance of an ID after 10 years of operation in a storage ring.
Optimization of the magnetic horn for the nuSTORM non-conventional neutrino beam using the genetic algorithm
This paper describes the strategy for optimizing the magnetic horn for the neutrinos from STORed Muons (nuSTORM) facility. The nuSTORM magnetic horn is the primary collection device for the secondary particles generated by bombarding a solid target with 120 GeV protons. As a consequence of the non-conventional beamline designed for nuSTORM, the requirements on the horn are different from those for a conventional neutrino beamline. At nuSTORM, muons decay while circulating in the storage ring, and the detectors are placed downstream of the production straight so as to be exposed to the neutrinos from muon decay. nuSTORM aims at precisely measuring the neutrino cross sections, and providing a definitive statement about the existence of sterile neutrinos. The nuSTORM horn aims at focusing the pions into a certain phase space so that more muons from pion decay can be accepted by the decay ring. The paper demonstrates a numerical method that was developed to optimize the horn design to gain higher neutrino flux from the circulating muons. A Genetic Algorithm (GA) was applied to the simultaneous optimization of the two objectives in this study. In conclusion, the application of the technique discussed in this paper is not limited to either the nuSTORM facility or muon based facilities, but can be used for other neutrino facilities that use magnetic horns as collection devices.
Mixing antiferromagnets to tune NiFe-[IrMn/FeMn] interfacial spin-glasses, grains thermal stability, and related exchange bias properties
Spintronics devices and in particular thermally assisted magnetic random access memories require a wide range of ferromagnetic/antiferromagnetic (F/AF) exchange bias (EB) properties and subsequently of AF materials to fulfil diverse functionality requirements for the reference and storage. For the reference layer, large EB energies and high blocking temperature (T{sub B}) are required. In contrast, for the storage layer, mostly moderate T{sub B} are needed. One of the present issues is to find a storage layer with properties intermediate between those of IrMn and FeMn and in particular: (i) with a T{sub B} larger than FeMn for better stability at rest-T but lower than IrMn to reduce power consumption at write-T and (ii) with improved magnetic interfacial quality, i.e., with reduced interfacial glassy character for lower properties dispersions. To address this issue, the EB properties of F/AF based stacks were studied for various mixed [IrMn/FeMn] AFs. In addition to EB loop shifts, the F/AF magnetic interfacial qualities and the AF grains thermal stability are probed via measurements of the low- and high-temperature contributions to the T{sub B} distributions, respectively. A tuning of the above three parameters is observed when evolving from IrMn to FeMn via [IrMn/FeMn] repetitions.
Re-Evaluation of Active Interlock Envelopes Considering Insertion Device Correction Coils
The Active Interlock (AI) is a system that ensures that the beam position and angle through the NSLS-II storage ring is located so that the machine apertures that may be struck by synchrotron radiation are not exposed to high power beam which may compromise them. Of particular importance in the NSLS-II is to maintain the beam position and angle within the insertion device (ID) straights where insertions devices make high power x-ray beams for users which may compromise the storage ring vacuum chamber. The beam position and angle in the center of the insertion device is calculated using a pair of beam position monitors (BPMs) on either side of the device. The safe area of positions and angles within the insertion device is called the AI envelope. If there is a magnetic element between the BPMs, it needs to be accounted for in the calculation of the beam position and angle. In addition to the permanent magnet arrays that comprise the insertion device itself, there are correction coils that are used to correct any orbit distortions that are generated by imperfections in the device. It has recently come to our attention that these coils are not considered in the AI calculations, nor are the currents in these coils read by the AI. As it may be possible in theory for these coils to produce angles large enough that the synchrotron radiation beam may damage components, we analyzed the possibility for all ID types and configurations. In this report we show what changes are necessary for the AI envelope, and limits placed upon the correction coils to maintain operation of the storage ring without compromising protection.
PROGRESS WITH NSLS-II INJECTION STRAIGHT SECTION DESIGN
The NSLS-II injection straight section (SR) consists of pulsed and DC bumps, septa system, beam trajectory correction and diagnostics systems. In this paper we discuss overall injection straight layout, preliminary element designs, specifications for the pulsed and DC magnets and their power supplies, vacuum devices and chambers and diagnostics devices. Prior to selecting the current 'conventional' design of the injection straight section we analyzed an option of injection via pulsed multipole pioneered at PF-AR. We found that this promising approach was not suited to the NSLS-II storage ring optics, since it would require a impractically compact arrangement of the injection straight section components and a complex modification of the transport line optics due to the strong focusing of the injected beam passing off the pulsed multipole axis. In addition, the requirement for a small injection transient of the stored beam orbit severely constrains the vertical alignment tolerance of the pulsed multipole. The design of the NSLS-II injection straight section is now completed with exception of transition chamber details, which will be adjusted to accommodate the actual layouts of the pulsed magnets.
A study of spin canting in Li{sub 3}Fe{sub 2}(PO{sub 4}){sub 3} with Mössbauer spectroscopy under 5 T
Li{sub 3}Fe{sub 2}(PO{sub 4}){sub 3} has been actively studied as a Lithium ion battery cathode material for the next-generation energy storage application. Here, we have investigated the changes of magnetic coupling between two different magnetic sub-lattices in Li{sub 3}Fe{sub 2}(PO{sub 4}){sub 3} with x-ray diffraction (XRD), superconducting quantum interference device (SQUID), and Mössbauer spectroscopy measurements. The experimental XRD pattern was analyzed using Rietveld refinement, confirming single phase. In order to investigate the magnetic property, the SQUID measurement under applied field of 5 T was performed between 4.2 and 295 K. From the temperature-dependent zero-field-cooled and field-cooled magnetization curves, we observed the magnetization decreasing with increasing temperature up to T{sub min} = 13 K, at which the magnetization showed a minimum value. With continuing increase in temperature, the magnetization starts increasing with a maximum value at T{sub max} = 28 K and beyond T{sub max}, the magnetization decreases with the further increase in temperature. Based on the experimentally measured Mössbauer spectra, we identified that the ratios of first and sixth to second and fifth absorption lines were identical around T{sub min}, while with increasing temperature the area of second and fifth absorption line rapidly decreased up to T{sub max}. Our study suggests that the spin canting angle between the applied field and hyperfine field of Li{sub 3}Fe{sub 2}(PO{sub 4}){sub 3} is constant up to T{sub min}. However, the spin canting angle starts decreasing with increasing temperature, reaching a minimum value at T{sub max}, and beyond T{sub max} it is increasing. We expect that around T{sub max}, the ferrimagnetically coupled spin arrangement is appeared to be collinear along the applied field direction under applied field of 5 T.
Spin Polarized Electron Emission Device
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Site-decorated model for unconventional frustrated magnets: Ultranarrow phase crossover and two-dimensional spin reversal transition
Here, the site-decorated Ising model is introduced to advance the understanding and experimental realization of the recently discovered one-dimensional (1D) finite-temperature ultranarrow phase crossover in an external magnetic field, while mitigating the geometric complexities of traditional bond-decorated models. The unconventional frustration and physics are clarified by exactly mapping the 1D site-decorated Ising model in a magnetic field onto a zero-field bond-decorated 𝐽 1 −𝐽 2 Ising model with conventional geometrical frustration. Furthermore, although higher-dimensional Ising models in an external field remain unsolved exactly, an exact solution for a spin-reversal transition—driven by an exotic, hidden half-ice, half-fire state induced by site decoration—is derived. This transition, triggered by a slight variation in temperature or magnetic field—without changing its direction—even in the weak-field limit, offers a promising route toward energy-efficient applications such as data storage and processing. The results suggest that site decoration offers an avenue for materials and device design, particularly in systems such as mixed 𝑑−𝑓 compounds, optical lattices, and neural networks, calling for further studies with site-decorated Heisenberg models. In addition, the site-decorated model offers a rigorous test ground for artificial intelligence (AI) in science, as the analytic derivation of the present results was not only validated but also improved by a general-purpose large language model, inspiring the use of AI as scientific discoverer.
Giant perpendicular magnetic anisotropy in Fe/III-V nitride thin films
Large perpendicular magnetic anisotropy (PMA) in transition metal thin films provides a pathway for enabling the intriguing physics of nanomagnetism and developing broad spintronics applications. After decades of searches for promising materials, the energy scale of PMA of transition metal thin films, unfortunately, remains only about 1 meV. This limitation has become a major bottleneck in the development of ultradense storage and memory devices. We discovered unprecedented PMA in Fe thin-film growth on the ($000\overline{1}$) N-terminated surface of III-V nitrides from first-principles calculations. PMA ranges from 24.1 meV/u.c. in Fe/BN to 53.7 meV/u.c. in Fe/InN. Symmetry-protected degeneracy between x 2 - y 2 and xy orbitals and its lift by the spin-orbit coupling play a dominant role. As a consequence, PMA in Fe/III-V nitride thin films is dominated by first-order perturbation of the spin-orbit coupling, instead of second-order in conventional transition metal/oxide thin films. This game-changing scenario would also open a new field of magnetism on transition metal/nitride interfaces.
Magnetoelectric coupling and spin-dependent tunneling in Fe/PbTiO{sub 3}/Fe multiferroic heterostructure with a Ni monolayer inserted at one interface
We report on first-principles calculations of a Ni monolayer inserted at one interface in the epitaxial Fe/PbTiO{sub 3}/Fe multiferroic heterostructure, focusing on the magnetoelectric coupling and the spin-dependent transport properties. The results of magnetoelectric coupling calculations reveal an attractive approach to realize cumulative magnetoelectric effects in the ferromagnetic/ferroelectric/ferromagnetic superlattices. The underlying physics is attributed to the combinations of several different magnetoelectric coupling mechanisms such as interface bonding, spin-dependent screening, and different types of magnetic interactions. We also demonstrate that inserting a Ni monolayer at one interface in the Fe/PbTiO{sub 3}/Fe multiferroic tunnel junction is an efficient method to produce considerable tunneling electroresistance effect by modifying the tunnel potential barrier and the interfacial electronic structure. Furthermore, coexistence of tunneling magnetoresistance and tunneling electroresistance leads to the emergence of four distinct resistance states, which can be served as a multistate-storage device. The complicated influencing factors including bulk properties of the ferromagnetic electrodes, decay rates of the evanescent states in the tunnel barrier, and the specific interfacial electronic structure provide us promising opportunities to design novel multiferroic tunnel junctions with excellent performances.
First-principles and model simulation of all-optical spin reversal
All-optical spin switching is a potential trailblazer for information storage and communication at an unprecedented fast rate free of magnetic fields. However, the current wisdom is largely based on semiempirical models of effective magnetic fields and heat pulses, so it is difficult to provide high-speed design protocols for actual devices. In this paper we carry out a massively parallel first-principles and model calculation for 13 spin systems and magnetic layers, free of any effective field, to establish a simpler and alternative paradigm of laser-induced ultrafast spin reversal and to point out a path to a full-integrated photospintronic device. It is the interplay of the optical selection rule and sublattice spin orderings that underlines seemingly irreconcilable helicity-dependent and -independent switchings. Using realistic experimental parameters, we predict that strong ferrimagnets, in particular, Laves phase C15 rare-earth alloys, meet the telecommunication energy requirement of 10 fJ, thus allowing a cost-effective subpicosecond laser to switch spin in the gigahertz region.
Electrostatic generator electrode-centering and seismic-isolation system for flywheel-based energy storage modules
Robust electro-static (ES) device embodiments, with application to energy storage flywheels as an example, are described that provide reliable, high-efficiency operation in the presence of thermal and mechanical perturbations, as well as seismic events. Electro-static generators and motors, when augmented with magnetic bearings, passive three-dimensional stabilization techniques and dynamic touch-down bearings, enable robust performance in the face of these environmental concerns, as well as efficient operation during typical operational sequences, including spin-up and steady-state modalities.
Electrostatic generator electrode-centering and seismic-isolation system for flywheel-based energy storage modules
Robust electro-static (ES) device embodiments, with application to energy storage flywheels as an example, are described that provide reliable, high-efficiency operation in the presence of thermal and mechanical perturbations, as well as seismic events. Electro-static generators and motors, when augmented with magnetic bearings, passive three-dimensional stabilization techniques and dynamic touch-down bearings, enable robust performance in the face of these environmental concerns, as well as efficient operation during typical operational sequences, including spin-up and steady-state modalities.
A New Superconducting Undulator Cryostat for the APS Upgrade
The Advanced Photon Source (APS) is in the midst of a major facility upgrade including both a new electron storage ring (SR) and many new insertion devices ( IDs) providing x-ray photon beams to a new suite of experimental end stations. Included among the new IDs are four 4.8-meter superconducting undulator (SCU) cryostats, each containing two 1.8-meter planar undulator magnets operating at 4.2 K in either a phase shifted or canted configuration. We describe a new, compact cryocooler-based cryostat design which supports the magnets and associated subsystems and also fits the space constraints of the SR ID straight sections. The design is an evolution of earlier single-magnet 2-meter cryostats, retaining some subsystem commonality while incorporating lessons learned and several features unique to the challenge of supporting two independently operable undulator magnets in a single device.
Color transparency and suppression of high-p{sub T} hadrons in nuclear collisions
The production length l{sub p} of a leading (large z{sub h}) hadron produced in hadronization of a highly virtual high-p{sub T} parton is short because of the very intensive vacuum gluon radiation and dissipation of energy at the early stage of the process. Therefore, the main part of nuclear suppression of high-p{sub T} hadrons produced in heavy ion collisions is related to the survival probability of a colorless dipole propagating through a dense medium. This is subject to color transparency, which leads to a steep rise with p{sub T} of the nuclear ratio R{sub AA}(p{sub T}), in good agreement with the recent data from the ALICE experiment at the CERN Large Hadron Collider (LHC). No adjustment, except for the medium density, is made, and the transport coefficient is found to be q{sub 0}=0.8 GeV{sup 2}/fm. This is close to the value extracted from the analysis of BNL Relativistic Heavy Ion Collider (RHIC) data for J/{Psi} suppression, but is an order of magnitude smaller than the value found from jet quenching data within the energy loss scenario. Although the present calculations have the status of a postdiction, the mechanism and all formulas have been published, and are applied here with no modification, except for the kinematics. At the same time, p{sub T} dependence of R{sub AA} at the energy of RHIC is rather flat due to the suppression factor steeply falling with rising x{sub T}, related to the energy conservation constraints. This factor is irrelevant to the LHC data, since x{sub T} is much smaller.
Giant Topological Hall Effect in van der Waals Heterostructures of CrTe 2 /Bi 2 Te 3
Discoveries of the interfacial topological Hall effect (THE) provide an ideal platform for exploring the physics arising from the interplay between topology and magnetism. The interfacial topological Hall effect is closely related to the Dzyaloshinskii-Moriya interaction (DMI) at an interface and topological spin textures. However, it is difficult to achieve a sizable THE in heterostructures due to the stringent constraints on the constituents of THE heterostructures, such as strong spin-orbit coupling (SOC). Here, we report the observation of a giant THE signal of 1.39 mu Omega.cm in the van der Waals heterostructures of CrTe 2 /Bi 2 Te 3 fabricated by molecular beam epitaxy, a prototype of two-dimensional (2D) ferromagnet (FM)/topological insulator (TI). This large magnitude of THE is attributed to an optimized combination of 2D ferromagnetism in CrTe 2 , strong SOC in Bi 2 Te 3 , and an atomically sharp interface. Furthermore, our work reveals CrTe 2 /Bi 2 Te 3 as a convenient platform for achieving large interfacial THE in hybrid systems, which could be utilized to develop quantum science and high-density information storage devices.