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Search indexed NASA NTRS and DOE OSTI research on propulsion, heat transfer, battery materials and energy systems. Follow report and document links to the original sources.

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At least 505 records · Page 28
All sourcesNASA NTRSDOE OSTI
DOE OSTI2019

Phase transitions and magnetic domain coexistence in Nd0.5Sr0.5MnO3 thin films

We present a study of the physical properties of perovskite oxide Nd 0.5 Sr 0.5 MnO 3 (NSMO) thin films grown on (110)-oriented SrTiO 3 substrates. In bulk form, NSMO displays coupled magnetic and electronic transitions from paramagnetic/insulator to ferromagnetic (FM)/metal and then to antiferromagnetic (AFM)/charge-ordered insulator with decreasing temperature. In thin films, the AFM ordering only occurs when the films exist in an anisotropic strain state such as those obtained on (110)-oriented cubic substrates. In this work, resonant X-ray reflectivity, soft X-ray photoemission electron microscopy (X-PEEM), and magnetometry measurements showed that the NSMO film displays both vertical and lateral magnetic phase separation. Specifically, the film consists of three layers with different density and magnetic properties. The FM and AFM properties of the main NSMO layer were probed as a function of temperature using soft X-ray magnetic spectroscopy, and the coexistence of lateral FM and AFM domains was demonstrated at 110 K using X-PEEM.

36 MATERIALS SCIENCE↗
DOE OSTI2015

Tailoring of magnetic properties of ultrathin epitaxial Fe films by Dy doping

We report on the controlled modification of relaxation parameters and magnetic moments of epitaxial Fe thin films through Dy doping. Ferromagnetic resonance measurements show that an increase of Dy doping from 0.1% to 5% gives a tripling in Gilbert damping, and more importantly a strongly enhanced anisotropic damping that can be qualitatively understood through the slow-relaxing impurity model. X-ray magnetic circular dichroism measurements show a pronounced suppression of the orbital moment of the Fe with Dy doping, leading to an almost threefold drop in the orbital to spin moment ratio, m{sub l}/m{sub s}. Doping with Dy can therefore be used to control both dynamic and static properties of thin ferromagnetic films for improved performance in spintronics device applications, mediated through the antiferromagnetic interaction of the 4f and 3d states.

36 MATERIALS SCIENCE↗
DOE OSTI2026

Long-range magnetic order and relaxor ferroelectricity in a hexagonal high-entropy ferrite

Multiferroics that combine ferroelectricity and magnetic order are attractive for electronic and spintronic technologies, yet chemical disorder that promotes relaxor ferroelectricity usually suppresses long-range magnetic order. Here, we report entropy-stabilized relaxor multiferroicity in epitaxial hexagonal (Tb0.2Dy0.2Ho0.2Lu0.2Yb0.2)FeO3 thin films. Structural, magnetic, dielectric, and synchrotron spectroscopic measurements show the coexistence of relaxor ferroelectricity and long-range ferromagnetic order. We find that improper ferroelectricity remains robust against A-site configurational disorder, while the Fe sublattice preserves magnetic exchange. This separation of the microscopic origins of the polar and magnetic responses enables chemically disordered multiferroicity. Our results establish entropy engineering in hexagonal ferrites as a route toward multifunctional oxide thin films and provide a general design strategy for high-entropy multiferroics.

Miertschin, Duncan [Baylor University]↗
DOE OSTI2018

Combined Technology Fabrication of Spin-Valve Magnetoresistive Elements and Micromagnets

We present the research results of the fabrication technology of magnetoresistive (MR) elements based on the multilayer spin-valve magnetoresistive (SVMR) Ta–FeNiCo–CoFe–Cu–CoFe–FeNiCo–FeMn–Та nanostructures and CoNi micromagnets for the construction of digital galvanic interchanges and the magnetic field sensors. The results of experimental studies of test elements based on multilayer SVMR nanostructures with an MR effect from 7 to 8% and films of magnetically hard materials with a coercive force of up to 95 Oe formed on a single silicon die are presented.

77 NANOSCIENCE AND NANOTECHNOLOGY↗
DOE OSTI2013

Magnetic and high frequency properties of nanogranular CoFe-TiO{sub 2} films

A series of soft magnetic nanogranular CoFe-TiO{sub 2} films with different thicknesses were fabricated on Si substrates by co-sputtering CoFe and TiO{sub 2}, and the magnetic and high frequency properties were studied in details. X-ray diffraction analysis confirmed that the films were nanocrystalline/amorphous composites. A saturation magnetization as high as 21 kGs and a ferromagnetic resonance (FMR) frequency above 3 GHz were obtained. It was found that the coercivity decreased steeply with the increase of film thickness and its minimum value was about 6 Oe. In addition, the variations of FMR peak broadness of the imaginary part and damping factor were also presented and discussed as functions of film thickness.

36 MATERIALS SCIENCE↗
DOE OSTI2015

X-ray magnetic circular dichroism study of epitaxial magnetite ultrathin film on MgO(100)

The spin and orbital magnetic moments of the Fe{sub 3}O{sub 4} epitaxial ultrathin film synthesized by plasma assisted simultaneous oxidization on MgO(100) have been studied with X-ray magnetic circular dichroism. The ultrathin film retains a rather large total magnetic moment, i.e., (2.73 ± 0.15) μ{sub B}/f.u., which is ∼70% of that for the bulk-like Fe{sub 3}O{sub 4}. A significant unquenched orbital moment up to 0.54 ± 0.05 μ{sub B}/f.u. was observed, which could come from the symmetry breaking at the Fe{sub 3}O{sub 4}/MgO interface. Such sizable orbital moment will add capacities to the Fe{sub 3}O{sub 4}-based spintronics devices in the magnetization reversal by the electric field.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2012

Effect of oxygen pressure on structural and magnetic properties of YIG thin films

The effect of oxygen pressure (P{sub O2}) on the Yttrium Iron Garnet (YIG) thin films were grown on silicon substrate by rf sputtering method was studied. The as-deposited films at 300K were amorphous in nature. The crystallization of these films was achieved by annealing at a temperature of 800 deg. C/1hr in air. The structural, microstructural and magnetic properties were found to be dependent on P{sub O2}.

36 MATERIALS SCIENCE↗
DOE OSTI2018

Electronic and Magnetic Structure of Intercalated Graphene Films

Ab initio calculations of the electron spectrum of the graphene–cobalt–nickel system were performed in the slope of the spin density functional theory (SDFT). Dispersion curves E{sub σn}(k) are presented; they were used to determine partial and total densities of valence electron states, and also magnetic moments of all atoms in the supercell. Energy position of the “Dirac cone” defined by p{sub z} states in graphene is shown to depend only slightly on the number of Co layers intercalated into the gap between the cobalt and graphene layers.

77 NANOSCIENCE AND NANOTECHNOLOGY↗
DOE OSTI2017

Transport properties of heteroepitaxial films based on bismuth telluride in strong magnetic fields

The temperature and magnetic-field dependences of the galvanomagnetic properties of n-Bi{sub 2}Te{sub 3} heteroepitaxial films in magnetic fields to 14 T at low temperatures are studied. It is shown that steps in the magnetic-field dependences of the quantum Hall effect and the plateau in the temperature dependences of the magnetoresistance of films are caused by topological surface states of Dirac fermions.

36 MATERIALS SCIENCE↗
DOE OSTI2012

Modified Magnetic Ground State in Nimn 2 O 4 Thin Films

The authors demonstrate the stabilization of a magnetic ground state in epitaxial NiMn 2 O 4 (NMO) thin films not observed in their bulk counterpart. Bulk NMO exhibits a magnetic transition from a paramagnetic phase to a collinear ferrimagnetic moment configuration below 110 K and to a canted moment configuration below 70 K. By contrast, as-grown NMO films exhibit a single magnetic transition at 60 K and annealed films exhibit the magnetic behavior found in bulk. Cation inversion and epitaxial strain are ruled out as possible causes for the new magnetic ground state in the as-grown films. However, a decrease in the octahedral Mn 4+ :Mn 3+ } concentration is observed and likely disrupts the double exchange that produces the magnetic state at intermediate temperatures. X-ray magnetic circular dichroism and bulk magnetometry indicate a canted ferrimagnetic state in all samples at low T. Together these results suggest that the collinear ferrimagnetic state observed in bulk NMO at intermediate temperatures is suppressed in the as grown NMO thin films due to a decrease in octahedral Mn 4+ , while the canted moment ferrimagnetic ordering is preserved below 60 K.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2022

Manipulating the metal-to-insulator transition and magnetic properties in manganite thin films via epitaxial strain

Strain engineering of epitaxial transition metal oxide heterostructures offers an intriguing opportunity to control electronic structures by modifying the interplay between spin, charge, orbital, and lattice degrees of freedom. Here, we demonstrate that the electronic structure, magnetic and transport properties of La 0.9 Ba 0.1 MnO 3 thin films can be effectively controlled by epitaxial strain. Spectroscopic studies and first-principles calculations reveal that the orbital occupancy in Mn eg orbitals can be switched from the d 3z 2 -r 2 orbital to the d x 2 -y 2 orbital by varying the strain from compressive to tensile. Further, the change of orbital occupancy associated with Mn 3d-O 2p hybridization leads to dramatic modulation of the magnetic and electronic properties of strained La 0.9 Ba 0.1 MnO 3 thin films. Under moderate tensile strain, an emergent ferromagnetic insulating state with an enhanced ferromagnetic Curie temperature of 215 K is achieved. These findings not only deepen our understanding of electronic structures, magnetic and transport properties in the La 0.9 Ba 0.1 MnO 3 system, but also demonstrate the use of epitaxial strain as an effective knob to tune the electronic structures and related physical properties for potential spintronic device applications.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2010

Finite element modeling of the deformation of magnetoelastic film

Recently a new class of biocompatible elastic polymers loaded with small ferrous particles, a magnetoelastic polymer, has been developed. This engineered material is formed into a thin film using spin casting. An applied magnetic field will deform the film. The magnetic deformation of this film has many possible applications, particularly in microfluidic pumps and pressure regulators. In this paper a finite element method suitable for the transient simulation of arbitrarily shaped three-dimensional magnetoelastic polymers subjected to time-varying magnetic fields is developed. The approach is similar to that employed in finite elment magnetohydrodynamic simulations, the key difference is a more complex hyperelastic material model. In order to confirm the validity of the approach, finite element solutions for an axially symmetric thin film are compared to an analytical solution based on the membrane (infinitely thin) approximation. For this particular problem the two approaches give qualitatively similar results and converge as the film thickness approaches zero.

36 MATERIALS SCIENCE↗
DOE OSTI2013

Multi-jump magnetic switching in ion-beam sputtered amorphous Co{sub 20}Fe{sub 60}B{sub 20} thin films

Unconventional multi-jump magnetization reversal and significant in-plane uniaxial magnetic anisotropy (UMA) in the ion-beam sputtered amorphous Co{sub 20}Fe{sub 60}B{sub 20}(5–75 nm) thin films grown on Si/amorphous SiO{sub 2} are reported. While such multi-jump behavior is observed in CoFeB(10 nm) film when the magnetic field is applied at 10°–20° away from the easy-axis, the same is observed in CoFeB(12.5 nm) film when the magnetic field is 45°–55° away from easy-axis. Unlike the previous reports of multi-jump switching in epitaxial films, their observance in the present case of amorphous CoFeB is remarkable. This multi-jump switching is found to disappear when the films are crystallized by annealing at 420 °C. The deposition geometry and the energy of the sputtered species appear to intrinsically induce a kind of bond orientation anisotropy in the films, which leads to the UMA in the as-grown amorphous CoFeB films. Exploitation of such multi-jump switching in amorphous CoFeB thin films could be of technological significance because of their applications in spintronic devices.

36 MATERIALS SCIENCE↗
DOE OSTI2014

Compositional dependence of magnetic and high frequency properties of nanogranular FeCo-TiO{sub 2} films

A series of soft magnetic nanogranular FeCo-TiO{sub 2} films with different compositions of FeCo were fabricated on Si substrates by co-sputtering FeCo and TiO{sub 2}, and the magnetic and high frequency properties were studied in details. X-ray diffraction analysis confirmed that the films were nanocrystalline/amorphous composites. A high saturation magnetization of 14 kGs, a low coercivity of 5.3 Oe, a FMR frequency of 3.2 GHz, and a high resistivity of 1068 μΩ cm were obtained when the volume fraction of FeCo was 0.68. The excellence electromagnetic properties make the films an excellent candidate for microwave applications.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2010

Ultrathin Co/Pt and Co/Pd superlattice films for MgO-based perpendicular magnetic tunnel junctions

Ultrathin [Co/Pt]{sub n} and [Co/Pd]{sub n} superlattice films consisting of 0.14-0.20-nm-thick Co and Pt(Pd) layers were deposited by sputtering. A large perpendicular magnetic anisotropy [(3-9)x10{sup 6} ergs/cm{sup 3}] and an ideal square out-of-plane hysteresis loop were attained even for ultrathin superlattice films with a total thickness of 1.2-2.4 nm. The films were stable against annealing up to 370 deg. C. MgO-based perpendicular magnetic tunnel junctions with this superlattice layer as the free layer showed a relatively high magnetoresistance ratio (62%) and an ultralow resistance-area product (3.9 {Omega} {mu}m{sup 2}) at room temperature. The use of these films will enable the development of gigabit-scale nonvolatile memory.

36 MATERIALS SCIENCE↗
DOE OSTI2014

Microstructure evolution and magnetic properties of FeB/Pt multilayers and FeBPt composite films

Comparisons of microstructural evolution and magnetic properties were made of a FeB12/Pt10/[FeB1.2/Pt1]{sub 15}/Ta5 nm multilayered structure with a FeB12/Pt10/FeBPt33/Ta5 nm co-deposited structure. The Ta capping layer was used to protect the films from oxidation. Both these samples were sputtered in the same planetary deposition system onto thermally oxidized silicon substrates. They both represent layer-by-layer deposition, with the second type of deposition having atomically fine layers, more than an order of magnitude finer than the first type. The samples were annealed at a range of times, temperatures, and vacuum conditions. X-ray diffraction (XRD), transmission electron microscopy, and alternating gradient magnetometry were employed to characterize the structural and magnetic properties, respectively. Significant differences were observed between the two types of structures. A maximum coercivity of 8.9 kOe was seen for the atomically fine multilayer, about 10% more than that for the coarse multilayer. XRD analysis confirmed that both the coarse and fine multilayers were in the L1{sub 0} phase after annealing. Our results indicate that the co-deposited film, which is really composed of atomically fine multilayers, is superior to the coarse multilayered FeB/Pt for the formation of L1{sub 0}-phase FePt.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2011

Room Temperature Ferromagnetism in Cu Doped ZnO Thin Films

We report on the growth of Cu doped ZnO thin films for different Cu concentration from 0.1%, to10% by RF magnetron sputtering. The X-ray diffraction study has shown single phase wurtzite type ZnO thin films with no evidence of copper/copper oxide or any other secondary phases. Room temperature ferromagnetism was observed in RF sputtered Cu doped ZnO films with magnetic moment per Cu atom first increasing and then decreasing with an increasing Cu content. Decrease of band gap with Cu doping, indicating strong p-d mixing of O and Cu is clear by the absorption spectroscopy study. The surface morphology by AFM of pure and Cu doped ZnO thin films show average grain size of 110nm and RMS surface roughness of 2.15 nm.

36 MATERIALS SCIENCE↗