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At least 1,063 records · Page 59
All sourcesNASA NTRSDOE OSTI
DOE OSTI2025

Unconventional Spintronics from Chiral Perovskites

Spintronic devices typically employ heterostructures with ferromagnets which break time-reversal symmetry and have non-vanishing magnetization. With the growing class of materials that support spin-polarized carriers, current, and excitations, it is possible to envision emerging spintronic applications that are not limited to magnetoresistance. Here, chiral perovskites with no net magnetization are considered, where the space-inversion and mirror symmetries are broken to induce chiral structure. The known importance of these perovskites is further expanded by the demonstration of the chiral-induced spin selectivity (CISS). However, the generation of the spin-polarized carriers across the interface with these chiral perovskites remains to be fully understood. These first-principles studies for 2D PbBr4-based chiral perovskites provide their electronic structure and an orbital-based symmetry analysis, which allows to establish an effective Hamiltonian to elucidate the underlying origin of their chirality. The same analysis is used for the Edelstein effect, responsible for electrical generation of the nonequilibrium spin polarization in many materials, which in chiral perovskites can be a mechanism contributing to CISS. Furthermore, by examining optical properties of chiral perovskites and the opportunity to use them to realize tunable altermagnets, another class of zero-magnetization spintronic materials, a versatile materials platform is put forth for unconventional spintronics.

14 SOLAR ENERGY↗
NASA NTRSDate not supplied

TPSAS-NF1676L-13664-DND

The safety of aerospace vehicles is largely dependent on the ability of modern non-destructive evaluation (NDE) tools to accurately detect structural damage before a critical flaw size is reached. However, existing NDE technologies are inherently limited by the physical response of the materials being inspected making the detection of small cracks or pre-crack damage difficult. One innovative solution to this problem is to create a multifunctional metallic material that can be used in structural applications and contains second phase sensory particles that significantly enhance the ability of conventional NDE techniques to detect incipient damage during use and at regularly scheduled inspections. Ferromagnetic shape-memory alloys (FSMAs) are an ideal material for use as this second phase material as they undergo a uniform and repeatable change in both magnetic properties and crystallographic structure when strained. These changes are more readily detected than small cracks, thereby, allowing for enhanced detection of damage by conventional NDE techniques. In this study, a multifunctional metallic material was produced by embedding the sensory material particles within an aluminum alloy to form a sensory alloy. The NDE response of the FSMA and the sensory alloy during tension/compression and fatigue loading have been investigated. These results suggest that sensory alloys can be utilized for improved on-board structural health monitoring and to improve the accuracy and reduce time for ground-based inspection.

T. A. Wallace↗
DOE OSTI2025

Predicted Ferromagnetism in Discovered Co–Bi Binary Phases

Binary solid-state materials offer unique insight into how the interplay of factors such as stoichiometry and bonding interactions affects magnetism and electronic properties. In this work, we considered systems where a transition metal provides the spin moment and a heavy main group element bolsters strong spin–orbit coupling. Within this context, cobalt, a known component of permanent magnets, and bismuth, functionally the heaviest element stable to radioactive decay, form a compelling combination. The Co–Bi system has been previously shown to exhibit superconductivity in a phase recovered from high pressure. We expected the Co−Bi system could also be ferromagnetic, resulting in two sets of compounds within one chemical system, one superconducting and one ferromagnetic. Subsequently, we investigated the Co–Bi system through both experimental and theoretical approaches to discover new candidates for permanent magnets. Ab initio random structure searching calculations identified five new compounds with diverse structural motifs that may form at higher pressures than previously reported. Experimental high-pressure synthesis yielded four compounds: α-CoBi, α-CoBi 2 , β-CoBi, and β-CoBi 2 . Three of these phases, α-CoBi 2 , β-CoBi, and β-CoBi 2 , were consistent with the calculated structures, corresponding to a 60% success rate for our structure search and underscoring the strength of combining computation with experiment. Theory predicts β-CoBi and β-CoBi2 are ferromagnetic, with β-CoBi possessing larger magnetocrystalline anisotropy energy than familiar permanent magnets such as CoPt and Nd–Fe–B. These results suggest the Co–Bi system could be a platform for understanding the factors that underpin magnetism and, to an extent, superconductivity in a chemically simple binary system.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2014

Enhanced ferromagnetic properties in Ho and Ni co-doped BiFeO{sub 3} ceramics

The magnetic properties of polycrystalline Bi{sub 1-x}Ho{sub x}Fe{sub 1-y}Ni{sub y}O{sub 3} (x = 0, 0.1; y = 0, 0.03), which were prepared by the solid-state method, have been investigated. The powder X-ray diffraction reveals that all the samples are polycrystalline and show rhombohedral perovskite structure. The micro-Raman scattering studies confirm that Bi{sub 0.9}Ho{sub 0.1}Fe{sub 0.97}Ni{sub 0.03}O{sub 3} has a compressive lattice distortion induced by the simultaneous substitution of Ho and Ni ions at A and B-sites, respectively. From the magnetization dependences at room temperature, Bi{sub 0.9}Ho{sub 0.1}Fe{sub 0.97}Ni{sub 0.03}O{sub 3} has enhanced magnetization (0.2280 emu/g) and low coercive field (280 Oe). It was revealed that the Ni dopant plays an important role for the improved ferromagnetic properties and the Ho dopant favors the magnetic exchange interactions in the co-doped ceramic.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2021

Evidence for anisotropic spin-triplet Andreev reflection at the 2D van der Waals ferromagnet/superconductor interface

Fundamental symmetry breaking and relativistic spin–orbit coupling give rise to fascinating phenomena in quantum materials. Of particular interest are the interfaces between ferromagnets and common s-wave superconductors, where the emergent spin-orbit fields support elusive spin-triplet superconductivity, crucial for superconducting spintronics and topologically-protected Majorana bound states. Here, we report the observation of large magnetoresistances at the interface between a quasi-two-dimensional van der Waals ferromagnet Fe 0.29 TaS 2 and a conventional s-wave superconductor NbN, which provides the possible experimental evidence for the spin-triplet Andreev reflection and induced spin-triplet superconductivity at ferromagnet/superconductor interface arising from Rashba spin-orbit coupling. The temperature, voltage, and interfacial barrier dependences of the magnetoresistance further support the induced spin-triplet superconductivity and spin-triplet Andreev reflection. This discovery, together with the impressive advances in two-dimensional van der Waals ferromagnets, opens an important opportunity to design and probe superconducting interfaces with exotic properties.

36 MATERIALS SCIENCE↗
DOE OSTI2016

Ferromagnetic and multiferroic interfaces in granular perovskite composite xLa{sub 0.5}Sr{sub 0.5}CoO{sub 3}-(1−x)BiFeO{sub 3}

Nanopowder of ferromagnetic La{sub 0.5}Sr{sub 0.5}CoO{sub 3} (LSCO) and multiferroic BiFeO{sub 3} (BFO) were synthesized by spray pyrolysis method. Different compositions of multiferroic xLSCO-(1−x)BFO composites were synthesized at 800 °C for 2 h. Scanning electron microscopy and energy dispersive spectroscopy elemental mapping were performed to study the morphology of composites. Ferri/ferromagnetic responses above T{sub C} (LSCO) are observed, which are associated with the interfaces LSCO/BFO. This interface presents a different behavior compared to the original perovskites, and the magnitude of the magnetization depends on x. Electrical DC conductivity as a function of temperature for LSCO nanopowder (x = 1) presents a different behavior than that reported in bulk material. For x = 1 and 0.9, the model by Glazman and Matveev [Zh. Eksp. Teor. Fiz. 94, 332 (1988)] is proposed to describe the electrical conductivity. On the other hand, x = 0, 0.1, and 0.5 present a variable range hopping behavior. Complex impedance spectroscopy as a function of frequency indicates a pure resistive behavior for x ≥ 0.5 compositions, while a complex resistive-capacitive behavior is observed for low x values (0, 0.1). In these samples, low values of magnetoelectric coupling were measured with an AC lock-in technique.

71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSIC↗
DOE OSTI2015

Magnetic phase transitions and monopole excitations in spin ice under uniaxial pressure: A Monte Carlo simulation

In this work, we explore the spin ice model under uniaxial pressure using the Monte Carlo simulation method. For the known spin ices, the interaction correction (δ) introduced by the uniaxial pressure varies in quite a wide range from positive to negative. When δ is positive, the ground state characterized by the ferromagnetic spin chains is quite unstable, and in real materials it serves as intermediate state connecting the ice state and the long range ordered dipolar spin ice ground state. In the case of negative δ, the system relaxes from highly degenerate ice state to ordered ferromagnetic state via a first order phase transition. Furthermore, the domain walls in such ferromagnetic state are the hotbed of the excitations of magnetic monopoles, thus indicating that the uniaxial pressure can greatly increase the monopole density.

71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSIC↗
DOE OSTI2018

Critical behavior in Ni 2 MnGa and Ni 2 Mn 0.85 Cu 0.15 Ga

The critical behaviors of polycrystalline Ni 2 MnGa and Ni 2 Mn 0.85 Cu 0.15 Ga have been examined through high-resolution bulk magnetization measurements. The critical exponents, β and γ, were derived from modified Arrott plots using the Kouvel-Fisher method. The values of the extracted critical exponents satisfied the scaling equation of state and associated exponent relations, indicating self-consistency of the extracted values. In Ni2MnGa, the critical exponents (β = 0.401 ± 0.003, γ = 1.27 ± 0.02) indicate a deviation from the 3D-Heisenberg values toward the mean-field values, likely due to the presence of long-range Ruderman-Kittel-Kasuya-Yosida interactions. However, the critical exponents of Ni2Mn0.85Cu0.15Ga (β = 0.389 ± 0.004, γ =1.39 ± 0.02) are closer to the 3D-Heisenberg values. This indicates a weakening of the long-range exchange interactions due to the substitution of Cu in the Mn site.

32 ENERGY CONSERVATION, CONSUMPTION, AND UTILIZATI↗
DOE OSTI2022

Coexisting structural disorder and robust spin-polarization in half-metallic FeMnVAl

We report half-metallic ferromagnets (HMFs) are one of the most promising materials in the field of spintronics due to their unique band structure, consisting of one spin subband having metallic characteristics along with another subband with semiconductor-like behavior. In this work, we report the synthesis of a novel quaternary Heusler alloy—FeMnVAl—and we have studied the structural, magnetic, transport, and electronic properties complemented with first-principles calculations. Among different possible structurally ordered arrangements, the optimal structure is identified by theoretical energy minimization. The corresponding spin-polarized band-structure calculations indicate the presence of a half-metallic ferromagnetic ground state. A detailed and careful investigation of the x-ray diffraction data, Mössbauer spectra, and nuclear magnetic resonance spectra suggests the presence of site disorder between the Fe and Mn atoms in the stable ordered structure of the system. The magnetic susceptibility measurement clearly establishes a ferromagnetic-like transition below ~213 K. The Fe Mössbauer spectrometry measurements suggest that only the Mn spins could be responsible for the magnetic order, which is consistent with our theoretical calculation. Surprisingly, the density-functional-theory calculations reveal that the spin-polarization value is almost immunized (92.4% → 90.4%) from the Mn-Fe structural disorder, even when nonmagnetic Fe and moment-carrying Mn sites are entangled inseparably. The robustness of spin polarization and half-metallicity in the studied FeMnVAl compound comprising structural disorder is thus quite interesting and could provide a new direction to investigate and understand the exact role of disorders on spin polarization in this class of materials, beyond the available knowledge.

71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSIC↗
DOE OSTI2019

Programmable Ultralight Magnets via Orientational Arrangement of Ferromagnetic Nanoparticles within Aerogel Hosts

The actuation and levitation of air-suspended objects by a magnetic field, due to its noncontact and holonomic manipulation modes, are important technological capabilities for device applications. However, owing to a higher density of conventional ferromagnets or nanoparticle-containing polymers and strong magnetic fields required for actuation, fabricating lightweight materials with a sensitive magnetic response for weight critical applications is challenging. Here, we report ultralight aerogel-based magnets (aero-magnets) comprising assembled ferromagnetic nanomaterials with highly magnetic anisotropy where the magnetic domains can be programmed by external predesigned fields. To demonstrate the breadth of manufacturing methods for this breed of aero-magnet composites, both silica/nanocellulose aerogel hosts and ferromagnetic nanorod/nanoplatelet guests have been explored. Single and double domains with out-of-plane magnetization are programmed into the aero-magnets and characterized by magnetic force microscopy. The levitation and actuation of the aero-magnets are realized while exposed to a small external magnetic field of 11 mT and introduced to a switching circuit. Furthermore, the elastic moduli of the aero-magnets are estimated by dynamic magnetic responses of the ferromagnetic nanoparticles tightly tethered in the aerogel hosts under rapid cyclic fields. These programmable aero-magnets could serve as monolithic magnetic actuator units in the fields of tiny robots and aerospace components.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2019

Interlayer RKKY coupling in bulk Rashba semiconductors under topological phase transition

The bulk Rashba semiconductors BiTeX (X=I, Cl and Br) with intrinsically enhanced Rashba spin-orbit coupling provide a new platform for investigation of spintronic and magnetic phenomena in materials. We theoretically investigate the interlayer exchange interaction between two ferromagnets deposited on opposite surfaces of a bulk Rashba semiconductor BiTeI in its trivial and topological insulator phases. In the trivial phase BiTeI, we find that for ferromagnets with a magnetization orthogonal to the interface, the exchange coupling is reminiscent of that of a conventional three-dimensional metal. Remarkably, ferromagnets with a magnetization parallel to the interface display a magnetic exchange qualitatively different from that of conventional three-dimensional metal due to the spin-orbit coupling. In this case, the interlayer exchange interaction acquires two periods of oscillations and decays as the inverse of the thickness of the BiTeI layer. For topological BiTeI, the magnetic exchange interaction becomes mediated only by the helical surface states and acts between the one-dimensional spin chains at the edges of the sample. The surface state-mediated interlayer exchange interaction allows for the coupling of ferromagnets with non-collinear magnetization and displays a decay power different from that of trivial BiTeI, allowing the detection of the topological phase transition in this material. Our work provides insights into the magnetic properties of these newly discovered materials and their possible functionalization.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2026

Evolution of magnetic bubble domains in the uniaxial ferromaget CeRu 2 Ga 2 B inferred from the Hall effect and ac magnetic susceptibility

We study the Hall effect, AC magnetic susceptibility (χ ac ), and magnetic force microscopy of the uniaxial ferromagnet CeRu 2 Ga 2 B with a centrosymmetric crystal structure. We observe a finite topological Hall effect (THE) within the ordered phase, before the magnetization is polarized by applied field. By comparing the field dependences of the area fraction of the magnetic bubbles, the derivative of χ ac , and the THE signal, we deduce that the magnetic bubbles in CeRu 2 Ga 2 B evolve from the trivial to topological spin texture with field. Our findings enable the expansion of the search for magnetic materials hosting topological spin textures to include uniaxial ferromagnets and open a new possibility to tailor the topological spin texture.

AC magnetic susceptibility↗
DOE OSTI2015

Room temperature ferromagnetism in Mg-doped ZnO nanoparticles

Zn{sub 1-x}Mg{sub x}O (x = 0, 0,10) nanoparticles were successfully synthesized using sol-gel method. X-ray diffraction (XRD) confirms that the synthesized nanoparticles possess wurtzite phase having hexagonal structure. Morphological analysis was carried out using transmission electron microscopy (TEM) which depicts the spherical morphology of ZnO nanoparticles. Energy dispersive spectroscopy (EDS) showed the presence of Mg in ZnO nanoparticles. Electron spin resonance (ESR) signal was found to be decreasing with increasing of Mg-doping concentration. The room temperature ferromagnetism was observed in undoped and Mg-doped ZnO nanoparticles. The increase of Mg-doping concentration resulted in decrease of saturation magnetization value which could be attributed to decrease of oxygen vacancies present in host nanoparticles.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2015

Structural and magnetic properties of pure and Cu doped In{sub 2}O{sub 3} thin films

Pure and Cu (7 at.%) doped In{sub 2}O{sub 3} thin films were prepared using an electron beam evaporation technique. A systematic study was carried out on the structural, chemical and magnetic properties of the thin films. X-ray diffraction analysis revealed that all the films were cubic in structure. The pure and Cu doped In{sub 2}O{sub 3} thin films showed ferromagnetism at room temperature. The Cu doped In{sub 2}O{sub 3} thin films showed the saturation magnetization, coercivity and retentivity of 38.71 emu/cm{sup 3}, 245 G and 5.54 emu/cm{sup 3}, respectively.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2021

Ferromagnetism out of charge fluctuation of strongly correlated electrons in κ -(BEDT-TTF) 2 Hg(SCN) 2 Br

We perform magnetic susceptibility and magnetic torque measurements on the organic κ-(BEDT-TTF) 2 Hg(SCN) 2 Br, which is recently suggested to host an exotic quantum dipole-liquid in its low-temperature insulating phase. Below the metal-insulator (MI) transition temperature, the magnetic susceptibility follows a Curie–Weiss law with a positive Curie–Weiss temperature, and a particular M∝ $\sqrt{H}$ curve is observed. The emergent ferromagnetically interacting spins amount to about 1/6 of the full spin moment of localized charges. Taking account of the possible inhomogeneous quasi-charge-order that forms a dipole-liquid, we construct a model of antiferromagnetically interacting spin chains in two adjacent charge-ordered domains, which are coupled via fluctuating charges on a Mott-dimer at the boundary. We find that the charge fluctuations can draw a weak ferromagnetic moment out of the spin singlet domains.

36 MATERIALS SCIENCE↗
DOE OSTI2014

Ubiquitous long-range antiferromagnetic coupling across the interface between superconducting and ferromagnetic oxides

The so-called proximity effect is the manifestation, across an interface, of the systematic competition between magnetic order and superconductivity. This phenomenon has been well documented and understood for conventional superconductors coupled with metallic ferromagnets; however it is still less known for oxide materials, where much higher critical temperatures are offered by copper oxide-based superconductors. In this paper, we show that, even in the absence of direct Cu–O–Mn covalent bonding, the interfacial CuO 2 planes of superconducting La 1.85 Sr 0.15 CuO 4 thin films develop weak ferromagnetism associated to the charge transfer of spin-polarised electrons from the La 0.66 Sr 0.33 MnO 3 ferromagnet. Theoretical modelling confirms that this effect is general to all cuprate/manganite heterostructures and the presence of direct bonding only affects the strength of the coupling. Finally, the Dzyaloshinskii–Moriya interaction, also at the origin of the weak ferromagnetism of bulk cuprates, propagates the magnetisation from the interface CuO 2 planes into the superconductor, eventually depressing its critical temperature.

36 MATERIALS SCIENCE↗
DOE OSTI2018

Single Domain 10 nm Ferromagnetism Imprinted on Superparamagnetic Nanoparticles Using Chiral Molecules

The rapid growth in demand for data and the emerging applications of Big Data require the increase of memory capacity. Magnetic memory devices are among the leading technologies for meeting this demand; however, they rely on the use of ferromagnets that creates size reduction limitations and poses complex materials requirements. Typically magnetic memory sizes are limited to 30–50 nm. Reducing the size even further, to the ≈10–20 nm scale, destabilizes the magnetization and its magnetic orientation becomes susceptible to thermal fluctuations and stray magnetic fields. In the present work, it is shown that 10 nm single domain ferromagnetism can be achieved. Using asymmetric adsorption of chiral molecules, superparamagnetic iron oxide nanoparticles become ferromagnetic with an average coercive field of ≈80 Oe. The asymmetric adsorption of molecules stabilizes the magnetization direction at room temperature and the orientation is found to depend on the handedness of the chiral molecules. These works point to a novel method for the miniaturization of ferromagnets (down to ≈10 nm) using established synthetic protocols.

36 MATERIALS SCIENCE↗