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At least 1,513 records · Page 84

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DOE OSTI2015

Pressure sensor

Disclosed is a passive, in-situ pressure sensor. The sensor includes a sensing element having a ferromagnetic metal and a tension inducing mechanism coupled to the ferromagnetic metal. The tension inducing mechanism is operable to change a tensile stress upon the ferromagnetic metal based on a change in pressure in the sensing element. Changes in pressure are detected based on changes in the magnetic switching characteristics of the ferromagnetic metal when subjected to an alternating magnetic field caused by the change in the tensile stress. The sensing element is embeddable in a closed system for detecting pressure changes without the need for any penetrations of the system for power or data acquisition by detecting changes in the magnetic switching characteristics of the ferromagnetic metal caused by the tensile stress.

47 OTHER INSTRUMENTATION↗

DOE OSTI2018

Sensor and methods of detecting target materials and situations in closed systems

47 OTHER INSTRUMENTATION↗

DOE OSTI2020

STRUCTURAL STABILITY OF MAGNETIC TUNNEL JUNCTION BASED MOLECULAR SPINTRONICS DEVICES (MTJMSD)

Harnessing the exotic properties of molecular level nanostructures to produce novel sensors, metamaterials, and futuristic computer devices can be technologically transformative. In addition, connecting the molecular nanostructures to ferromagnetic electrodes bring the unprecedented opportunity of making spin property based molecular devices. We have demonstrated that magnetic tunnel junction based molecular spintronics device (MTJMSD) approach to address numerous technological hurdles that have been inhibiting this field for decades. MTJMSD approach is based on producing a capacitor like a testbed where two metal electrodes are separated by an ultrathin insulator and subsequently bridging the molecule nanostructure across the insulator to transform a capacitor into a molecular device. Our prior work showed that MTJMSDs produced extremely intriguing phenomenon such as room temperature current suppression by six orders, spin photovoltaic effect, and evolution of new forms of magnetic metamaterials arising due to the interaction of the magnetic a molecule with two ferromagnetic thin films. However, making robust and reproducible electrical connections with exotic molecules with ferromagnetic electrodes is full of challenges and requires attention to MTJMSD structural stability. This paper focuses on MTJMSD stability by describing the overall fabrication protocol and the associated potential threat to reliability. MTJMSD is based on microfabrication methods such as (a) photolithography for patterning the ferromagnetic electrodes, (b) sputtering of metallic thin films and insulator, and (c) at the end electrochemical process for bridging the molecules between two ferromagnetic films separated by ~ 2nm insulating gap.

36 MATERIALS SCIENCE↗

DOE OSTI2014

Structural and magnetic properties of irradiated SiC

We present a comprehensive structural characterization of ferromagnetic SiC single crystals induced by Ne ion irradiation. The ferromagnetism has been confirmed by electron spin resonance, and possible transition metal impurities can be excluded to be the origin of the observed ferromagnetism. Using X-ray diffraction and Rutherford backscattering/channeling spectroscopy, we estimate the damage to the crystallinity of SiC, which mutually influences the ferromagnetism in SiC.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗

DOE OSTI2014

Multi-state magnetoresistance in ferromagnet/organic-ferromagnet/ferromagnet junctions

Spin-dependent transport through a ferromagnetic metal/organic-ferromagnet/ferromagnet metal junction is investigated theoretically. It is demonstrated that the current through the device strongly depends on the alignment of the magnetization orientations of the electrodes and interlayer. The spin-related electron tunnelling between the ferromagnetic electrodes suffers a further spin selection induced by the spin-polarized states of the central organic ferromagnet. This work indicates an intriguing prospect of organic ferromagnets in spintronic devices, such as four-state magnetoresistance manipulated by a magnetic field.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗

DOE OSTI2014

Electronic structure, magnetic properties, and magnetostructural transformations in rare earth dialuminides

We report electronic structure, magnetic properties, and magnetostructural transformations of selected rare earth dialuminides calculated by using local spin density approximation (LSDA), including the Hubbard U parameter (LSDA + U) approach. Total energy calculations show that CeAl{sub 2} and EuAl{sub 2} adopt antiferromagnetic (AFM) ground states, while dialuminides formed by other magnetic lanthanides have ferromagnetic (FM) ground states. The comparison of theoretical and experimental magnetic moments of CeAl{sub 2} indicates that the 4f orbital moment of Ce in CeAl{sub 2} is quenched. Theoretical calculations confirm that Eu in EuAl{sub 2} and Yb in YbAl{sub 2} are divalent. PrAl{sub 2} exhibits a tetragonal distortion near FM transition. HoAl{sub 2} shows a first order magnetostructural transition while DyAl{sub 2} shows a second order transformation below magnetic transition. The dialuminides formed by Nd, Tb, and Er are simple ferromagnets without additional anomalies in the FM state.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗

DOE OSTI2015

The magnetic particle in a box: Analytic and micromagnetic analysis of probe-localized spin wave modes

The dipole field from a probe magnet can be used to localize a discrete spectrum of standing spin wave modes in a continuous ferromagnetic thin film without lithographic modification to the film. Obtaining the resonance field for a localized mode is not trivial due to the effect of the confined and inhomogeneous magnetization precession. We compare the results of micromagnetic and analytic methods to find the resonance field of localized modes in a ferromagnetic thin film, and investigate the accuracy of these methods by comparing with a numerical minimization technique that assumes Bessel function modes with pinned boundary conditions. We find that the micromagnetic technique, while computationally more intensive, reveals that the true magnetization profiles of localized modes are similar to Bessel functions with gradually decaying dynamic magnetization at the mode edges. We also find that an analytic solution, which is simple to implement and computationally much faster than other methods, accurately describes the resonance field of localized modes when exchange fields are negligible, and demonstrating the accessibility of localized mode analysis.

71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSIC↗

DOE OSTI2015

Comparative study of magnetic ordering in bulk and nanoparticles of Sm{sub 0.65}Ca{sub 0.35}MnO{sub 3}: Magnetization and electron magnetic resonance measurements

To explore the effect of size reduction to nanoscale on the hole doped Sm{sub 0.65}Ca{sub 0.35}MnO{sub 3} compound, dc magnetic measurements and electron magnetic resonance (EMR) were done on bulk and nanoparticle samples in the temperature range 10 ≤ T ≤ 300 K. Magnetization measurement showed that the bulk sample undergoes a charge ordering transition at 240 K and shows a mixed magnetic phase at low temperature. However, the nanosample underwent a ferromagnetic transition at 75 K, and the charge ordered state was destabilized on size reduction down to nanoscale. The low-temperature ferromagnetic component is found to be enhanced in nanoparticles as compared to their bulk counterpart. Interestingly around room temperature, bulk particles show higher magnetization where as at low temperature nanoparticles show higher magnetization. Ferromagnetism in the bulk is due to super exchange where as ferromagnetism in nanoparticles is due to uncompensated spins of the surface layer. Temperature variation of EMR parameters correlates well with the results of magnetic measurements. The magnetic behaviour of the nanoparticles is understood in terms of the core shell scenario.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗

DOE OSTI2019

Microscopic subsurface characterization of layered magnetic materials using magnetic resonance force microscopy

This project resulted in the following accomplishments: 1) The invention of scanned probe ferromagnetic resonance microscopy. Upon implementation and refinement this approach was used to measure static and dynamic magnetic resonance properties of ferromagnets with an unprecedented combination of spectral and spatial resolution. 2) Demonstration and study of spin pumping in a pristine ferromagnet across a boundary defined entirely by a magnetic field gradient, and so free of materials discontinuities. 3) First demonstrated highly efficient dynamic spin injection from Y 3 Fe 5 O 12 (YIG) into NiO, an antiferromagnetic (AF) insulator and robust spin propagation in AF NiO over distances up to 100-nm thickness; both spin injection and spin transport are mediated by the AF spin correlations. 4) Demonstration of exceptionally high efficiency conversion of spin current to charge current achieved in spin pumping from the dynamic magnetization of a ferromagnetic insulator into a variety of adjacent metal films. 5) Seminal study of the nature of spin-orbit coupling in d-electron metals that revealed the dominant sensitivity of the d-orbital moment to the d-electron count and revealing the important roles of both d-electron configuration and atomic number in the physics of the spin Hall effect. 6) Demonstration of observation of FMR by means of optically-detected NV diamond relaxometry that provided a highly sensitive, spatially resolved FMR detection method and revealed spin pumping across 100-nm length scales by means of dipolar coupling. 7) Using magnetic field localization, developed for FMR imaging, demonstrated a novel approach to discretizing spin wave modes to improve the characteristics of auto-oscillators driven by pure spin currents produced by the spin Hall effect. 8) We demonstrated large spin pumping signals from propagating high wavevector spinwaves in thin film YIG find that the spin pumping efficiency was insensitive to wavevector thus emphasizing the promise of thin YIG films for spinwave-based spintronics by allowing for predictable down-scaling of device dimensions and enabling a broad range of operational frequencies.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗

DOE OSTI2024

Medium-Entropy Engineering of Magnetism in Layered Antiferromagnet Cu x Ni 2(1- x ) Cr x P 2 S 6

Antiferromagnetic van der Waals-type M 2 P 2 X 6 compounds provide a versatile material platform for studying 2D magnetism and relevant phenomena. Establishing ferromagnetism in 2D materials is technologically valuable. Though magnetism is generally tunable via a chemical way, it is challenging to induce ferromagnetism with isovalent chalcogen and bimetallic substitutions in M 2 P 2 X 6 . Here, we report co-substitution of Cu 1+ and Cr 3+ for Ni 2+ in Ni 2 P 2 S 6 , creating Cu x Ni 2(1-x) Cr x P 2 S 6 medium-entropy alloys spanning a full substitution range (x = 0 to 1). Such substitution strategy leads to a unique evolution in crystal structure and magnetic phases that are distinct from traditional isovalent bimetallic doping, with Cu and Cr co-substitution enhancing ferromagnetic correlations and generating a weak ferromagnetic phase in intermediate compositions. This aliovalent substitution strategy offers a universal approach for tuning layered magnetism in antiferromagnetic systems, which along with the potential for light-matter interaction and high-temperature ferroelectricity, can enable multifunctional device applications.

2D magnetism↗

DOE OSTI2026

Ultrafast Terahertz Field Control of the Emergent Magnetic and Electronic Interactions at Oxide Interfaces

Ultrafast electric-field control of emergent electronic and magnetic states at oxide interfaces offers exciting prospects for the development of the next generation of energy-efficient devices. Here, it is demonstrated that the electronic structure and emergent ferromagnetic interfacial state in epitaxial LaNiO3/CaMnO3 superlattices can be effectively controlled using intense, single-cycle THz electric-field pulses. A suite of advanced X-ray spectroscopic techniques is employed to measure a detailed magneto-optical profile and the thickness of the ferromagnetic interfacial layer. Then, a combination of time-resolved and temperature-dependent optical measurements is used to disentangle several correlated electronic and magnetic processes driven by ultrafast, high-field THz pulses. Sub-picosecond non-equilibrium Joule heating of the electronic system is observed, ultrafast demagnetization of the ferromagnetic interfacial layer, and slower dynamics indicative of a change in the magnetic state of the superlattice due to the transfer of spin-angular momentum to the lattice. These findings suggest a promising avenue for the efficient control of 2D ferromagnetic states at oxide interfaces using ultrafast electric-field pulses.

X-ray spectroscopy and scattering↗

DOE OSTI2018

Effect of Tuning the Structure on the Optical and Magnetic Properties by Various Transition Metal Doping in ZnO/TM (TM = Fe, FeCo, Cr, and Mn) Thin Films

We have investigated in this work the physical, optical, electronic, and the magnetic behavior (Curie temperature, magnetic moment) of Zn.1-x.MxO (M = Fe 5%, Co 1%, Cr 5%, and Mn 5%), diluted magnetic semiconductors (DMSs). The samples were deposited on glass substrate by the spray pyrolysis technique, and the results of the x-ray diffraction (XRD) of the prepared substrates was used to prove the incorporation of the dopants into the ZnO lattice host; the ferromagnetic and the antiferromagnetic state competitions and their effects on the physical, magnetic, and optical properties, were investigated. The electronic structure and magnetic properties of transition metal (TM) defects, were investigated in detail, by using the Korringa–Kohn–Rostoker (KKR) method combined with the coherent potential approximation (CPA). As a result, doping by TM impurities induce the ferromagnetism with different competitions between the ferromagnetic and antiferromagnetic states, which affects the physical properties of the TM (Fe, Fe/Co, Cr, and Mn)-doped ZnO, with a Curie temperature closer to room-temperature ferromagnetic.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗

DOE OSTI2018

Effect of Fe Substitution on Microstructure and Magnetic Properties of Ni{sub 1−x}Fe{sub x}O{sub 2} Nanoparticles

Fe-substituted NiO nanoparticles (Ni{sub 1−x}Fe{sub x}O{sub 2}) (x= 0.00, 0.03, 0.05, 0.07, and 0.09) were synthesised using ball-milling method followed by vacuum sintering and studied for their microstructural and magnetic properties. All the samples show a cubic structure with a crystallite size of 17–26 nm. Secondary phases related to Fe{sub 2}O{sub 3} were identified from XRD, indicating that the observed ferromagnetism may be due to the dopants. The doping of Fe ions does not cause any significant variation in the crystal structure. The pure NiO nanoparticles were weak ferromagnetic in nature, and Fe-doped NiO nanoparticles exhibit room temperature ferromagnetism. The strength of magnetization increased from 0.57 to 0.94 emu/g with an increase of Fe concentration from 3 to 7 at.%, respectively. A high coercive field of 173 Oe was observed for the Ni{sub 1−x}Fe{sub x}O{sub 2} nanoparticles at x= 0.09. The results and the process of development of ferromagnetism at room temperature in the Ni{sub 1−x}Fe{sub x}O{sub 2} nanoparticles were presented and discussed in detail.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗

DOE OSTI2019

Effect of Fe Doping and Point Defects (V{sub O} and V{sub Sn}) on the Magnetic Properties of SnO{sub 2}

We investigated the effects of Fe doping and point defects (oxygen and tin vacancies, V{sub O} and V{sub Sn}, respectively) on the ferromagnetism of SnO{sub 2} through first-principles calculations by using generalized gradient approximation + U under density functional theory. Calculation results show that Fe-doped SnO{sub 2} with V{sub O} or V{sub Sn} exhibit long-range ordered ferromagnetism and Curie temperature above room temperature. The system has different magnetic properties with different doping modes, which are beneficial to the magnetic adjustment of dilute magnetic semiconductor (DMS). The double-exchange effects among the electrons of O–2p and Fe–3d states are the origin of ferromagnetism in Sn{sub 15}FeO{sub 31}. Similarly, ferromagnetism in Sn{sub 14}FeO{sub 32} is derived from the double-exchange effects among the electrons of O–2p and Fe–3d states. These effects are produced by hole carriers after complexes form by Fe doping and V{sub O} or V{sub Sn}. Simultaneously, Sn{sub 14}FeO{sub 32} shows a half-metallic behavior, thus resulting in 100% conduction hole polarizability, which is highly beneficial to DMSs as a hole-injection source. Moreover, results also show that the decreased distance between Fe and vacancies (V{sub O} or V{sub Sn}) lowers formation energy and thus increases the system stability.

36 MATERIALS SCIENCE↗

DOE OSTI2019

Effects of Oxygen Vacancy on the Magnetic Properties of Ni-Doped SnO{sub 2} Nanoparticles

We studied the ferromagnetism of Ni-doped SnO{sub 2} with and without oxygen vacancy (V{sub O}) by experiments and calculations. Sn{sub 0.96}Ni{sub 0.04}O{sub 2} nanocrystalline powder prepared by the sol-gel method exhibits room-temperature ferromagnetism, and the vacuum annealing reduces its saturation magnetizations. The density functional theory (DFT) calculations show that the doped Ni atom can introduce a local magnetic moment of about 2.0 μ{sub B} in SnO{sub 2} (110) surface, which is ascribed to the spin-polarization of Ni 3d and O 2p electrons. The type of preferential magnetic coupling of Ni-doped SnO{sub 2} (110) surface depends upon the distributions of Ni dopants, and ferromagnetic coupling is more favorable in most cases. Introduction of V{sub O} obviously weakens the ferromagnetic interaction of Ni-doped SnO{sub 2} (110) surface, which can give a reasonable explanation for our experimental observations.

77 NANOSCIENCE AND NANOTECHNOLOGY↗

DOE OSTI2019

Investigation on Electronic Structures and Magnetic Properties of (Mn, Ga) Co-doped SnO{sub 2}

The electronic structures and magnetic properties of (Mn, Ga) co-doped SnO{sub 2} are studied by the first-principles calculations in full-potential linearized augmented plane wave formalism within generalized gradient approximations. We found that the doped system favors the ferromagnetic state and room-temperature ferromagnetism can be expected in it. The origin of ferromagnetism can be attributed to p-d exchange interactions as Mn-O-Mn. Ga acts as acceptor in (Mn, Ga) co-doped SnO{sub 2} host and can donate one hole, increasing the carrier concentration and thus leading to a more stable ferromagnetic state. These results suggest a recipe obtaining promising dilute magnetic semiconductor by doping nonmagnetic elements in SnO{sub 2} matrix.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗

DOE OSTI2019

Electronic structures and magnetic performance related to spintronics of Sr{sub 0.875}Ti{sub 0.125}S

In this study, we have used the first-principle approaches of density functional theory to determine the electronic and magnetic performances related to spintronics applications of titanium (Ti)-substituted SrS such as Sr{sub 1−x}Ti{sub x}S at concentration x = 0.125. The results of electronic and magnetic properties by using TB–mBJ potential revealed that Sr{sub 0.875}Ti{sub 0.125}S compound is half-metallic ferromagnetic with a half-metallic gap and a spin polarization of 100%. The ferromagnetic nature of Sr{sub 0.875}Ti{sub 0.125}S material is confirmed by the ferromagnetic coupling between magnetic moments of Ti, Sr and S atoms. The total magnetic moment of integer Bohr magneton of 2 μ{sub B} and the large half-metallic gap of 1.245 suggest that this compound is a true half-metallic ferromagnet.

36 MATERIALS SCIENCE↗

DOE OSTI2015

Double-exchange mechanism in rare-earth compounds

We show that double-exchange mechanism is responsible for ferromagnetism in low dimensional rare-earth compounds. We use the bosonized version of the one-dimensional Anderson lattice model in Toulouse limit to characterize the properties of the emerging ferromagnetic phase. We give a comprehensive description of the ferromagnetic ordering of the correlated electrons which appears at intermediate couplings and doping. The obtained ferromagnetic phase transitions have been identified to be an order–disorder transition of the quantum random transverse-field Ising type.

71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSIC↗