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All sourcesNASA NTRSDOE OSTI
DOE OSTI2026

Mixed Nd 4+/3+ and Cluster Magnetism in Hexagonal Perovskite 12R-Ba 4 NdMn 3 O 12−γ

Hexagonal perovskite oxides with 12R stacking host well-separated face-sharing octahedral metal trimers with short metal–metal distances, leading in some cases to large degrees of magnetic frustration and cluster magnetism. Introducing magnetic ions in proximity to these trimers can influence the degree of frustration and cluster magnetism, but the extent to which the magnetism can be tuned by varying neighboring metal cations remains an open question. In this work, we test the impacts of using Nd in proximity to Mn trimers in the hexagonal perovskite 12R-Ba 4 NdMn 3 O 12−γ . Given this stoichiometry, Nd should assume the 4+ oxidation state with a spin state of S = 1, which would be the first realization of Nd 4+ in an oxide environment. Through detailed bulk magnetic, X-ray absorption spectroscopic, and powder neutron diffraction (PND) measurements, we find that Nd 4+ is realized in this material, but there is also partial reduction to Nd 3+ , which is charge-balanced by O vacancies. Magnetometry measurements indicate an antiferromagnetic ordering temperature T N ≈ 16 K, and PND measurements reveal a surprising collinear antiferromagnetic structure with magnetic space group Pc2/m (no. 10.49 in BNS notation), which has not previously been seen in this class of materials. Our results represent a comprehensive analysis of the structural, electronic, and magnetic properties of 12R-Ba 4 NdMn 3 O 12−γ , showing the first observation of partial Nd 4+ in an oxide, and demonstrating that this structural class can host a broad range of magnetic structures which are not easily predicted based on compositional trends.

14 SOLAR ENERGY↗
DOE OSTI2016

Theoretical study of NMR, infrared and Raman spectra on triple-decker phthalocyanines

Electronic structures and magnetic properties of multi-decker phthalocyanines were studied by theoretical calculation. Electronic structures, excited processes at multi-states, isotropic chemical shifts of {sup 13}C, {sup 14}N and {sup 1}H-nuclear magnetic resonance (NMR), principle V-tensor in electronic field gradient (EFG) tensor and asymmetry parameters (η), vibration mode in infrared (IR) and Raman spectra of triple-decker phthalocyanines were calculated by density functional theory (DFT) and time-dependent DFT using B3LYP as basis function. Electron density distribution was delocalized on the phthalocyanine rings with electron static potential. Considerable separation of chemical shifts in {sup 13}C, {sup 14}N and {sup 1}H-NMR was originated from nuclear spin interaction between nitrogen and carbon atoms, nuclear quadrupole interaction based on EFG and η of central metal under crystal field. Calculated optical absorption at multi-excited process was derived from overlapping π-orbital on the phthalocyanine rings. The vibration modes in IR and Raman spectra were based on in-plane deformation and stretching vibrations of metal-ligand coordination bond on the deformed structure.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2018

A Role of the 3d Electron Subsystem in the Evolution of Band Structure and Magnetic and Optical Properties of ErNi{sub 5 –} {sub x}Co{sub x} Compounds (x = 0–4)

The evolution of the electronic structure and optical and magnetic properties of ErNi{sub 5 –} {sub x}Co{sub x} compounds (x = 0–4), occurring upon substitution of nickel by cobalt atoms, has been investigated. Spin-polarization calculations of the band spectrum of these intermetallic compounds have been performed within the local spin density approximation with a correction for strong electron correlations in the 4f shell of a rare-earth ion (method LSDA+U). The values of magnetic moments for erbium, nickel, and cobalt ions (located at different crystallographic sites) are obtained. The exchange-interaction parameters for the 3d sublattice of transition metals are determined. The spectral properties of the compounds have been investigated in the wavelength range of 0.22–15 μm by optical ellipsometry. The experimental frequency dependences of the optical conductivity in the interband absorption region are compared with the corresponding characteristics calculated based on the density of electronic states.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2018

Strong Correlation Effect in Ferrimagnetic Half-Metallic V{sub 2}CoAl and V{sub 2}CoGa Heusler Compounds

We present first-principles calculations based on the full-potential linearized augmented plane wave (FP-LAPW) method to investigate the structural, elastic, electronic, and magnetic properties of the Heusler compounds V{sub 2}CoAl and V{sub 2}CoGa. We explore different magnetic configurations in both regular and inverse Heusler structures: the Cu{sub 2}MnAl-type and Hg{sub 2}CuTi-type structures respectively. Our compounds are found to be ferrimagnets in the inverse Heusler structure. To take into account the effects of the strong correlation among the localized d-states, we perform a calculation using the GGA+U method (the general gradient approximation with the Hubbard on-site Coulomb correction U). Then we show that both compounds exhibit a half-metallic character and have a magnetic moment of 2.00 μ{sub B} per formula unit. This latter statement is coherent with the generalized Slater-Pauling rule (SP). In terms of the band structure calculations, we explain the formation of the indirect energy band gaps in the spin-majority channels. We also use the mean-field approximation (MFA) to discuss the magnetic exchange couplings and predict the Curie temperature for both compounds.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2018

Calculations of the Structural, Elastic, Magnetic, and Electronic Properties of the New Compound BaZr{sub 0.5}Mn{sub 0.5}O{sub 3} with Tetragonal Structure

Based on the density functional theory, we have calculated the structural properties of the BaZrO{sub 3} (BZO) cubic structure with PBE-GGA, PBEsol-GGA, and LDA approximations. The equilibrium lattice constant within GGA-PBEsol (a = 4.1847 Å) is in very good agreement with the experimental data (Holland and Redfern, Miner. Mag. 61: 65, 1997). The calculations of elastic properties of pure and doped BaZrO{sub 3} are calculated with PBEsol-GGA; both BZO and BZM are compressible and show a brittle nature. According to calculated electronic and magnetic properties, it is found that Mn-doped BaZrO{sub 3} system is a half metallic and exhibits a ferromagnetic character. The total magnetic moment of the cell is equal to3.57 µ{sub B}; this value comes from manganese atom (Mn) with a value of 3.176 µ{sub B}. The magnetic moments of barium, oxygen, and zirconium atoms are approximately equal to zero.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2018

Effect of Cu dopant on the structural, magnetic and electrical properties of Ni-Zn ferrites

Highlights: • Ni{sub 0.8-x}Cu{sub x}Zn{sub 0.2}Fe{sub 2}O{sub 4} (x = 0.0, 0.2, 0.4, 0.6) Spinel ferrites synthesized through auto-combustion method and their structural and magnetic properties investigated by XRD, SEM, FTIR and VSM measurements. • Increase in crystal and particle size and decrease in saturation magnetization resulted from substitution on Ni by Cu. • Observed values of (ε) and (tanδ) of the samples show the deterministic role of density in electrical properties of spinel ferrites. - Abstract: Ni{sub 0.8-x}Cu{sub x}Zn{sub 0.2}Fe{sub 2}O{sub 4} (x = 0.0, 0.2, 0.4, 0.6) ferrite was synthesized through auto-combustion method. (XRD) patterns confirmed the crystallization of the samples in spinel structure. FESEM showed that the size of ferrite particles are about few hundred nanometers and with increase in Cu concentration (x) in the structure there is increase in particle size. Fourier transform infrared (FTIR) spectrometry indicates that octahedral and tetrahedral sites are formed. Vibrating sample magnetometer (VSM) results proved reduction of saturation magnetization (M{sub s}) by increasing Cu content, which is explained according to the ferrimagnetic nature of these samples in which Ni is replaced by Cu at octahedral site. Real part of dielectric constant (ε) and loss tangent (tanδ) of samples were also studied in frequency range of 100–20000 Hz. Results showed an increase in ε and tanδ of the sample with x = 0.6 which is considered to be the result of higher density of this sample.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2018

Magnetic and Magnetodielectric Properties of Ho{sub 0.5}Nd{sub 0.5}Fe{sub 3}(BO{sub 3}){sub 4}

The magnetic and magnetodielectric properties of Ho{sub 0.5}Nd{sub 0.5}Fe{sub 3}(BO{sub 3}){sub 4} ferroborate with the competing Ho–Fe and Nd–Fe exchange couplings have been experimentally and theoretically investigated. Step anomalies in the magnetization curves at the spin-reorientation transition induced by the magnetic field B ║ c have been found. The spontaneous spin-reorientation transition temperature T{sub SR} ≈ 8 K has been refined. The measured magnetic properties and observed features are interpreted using a single theoretical approach based on the molecular field approximation and calculations within the crystal field model of the rare-earth ion. Interpretation of the experimental data includes determination of the crystal field parameters for Ho{sup 3+} and Nd{sup 3+} ions in Ho{sub 0.5}Nd{sub 0.5}Fe{sub 3}(BO{sub 3}){sub 4} and parameters of the Ho–Fe and Nd–Fe exchange couplings.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2015

Optimization of L1{sub 0} FePt/Fe{sub 45}Co{sub 55} thin films for rare earth free permanent magnet applications

The magnetic properties of magnetron sputtered bilayers consisting of Fe{sub 45}Co{sub 55} ultrathin layers on top of L1{sub 0} FePt films epitaxially grown on MgO substrates are studied in view of their possible application as rare earth free permanent magnets. It is found that FePt layers induce a tetragonal distortion to the Fe-Co layers which leads to increased anisotropy. This allows to take advantage of the Fe-Co high magnetic moment with less significant loss of the coercivity compared to a typical hard/soft exchange spring system. A maximum energy product approaching 50 MGOe is obtained for a FePt(7 ML)/FeCo/(5 ML) sample. The results are in accordance with first-principles computational methods, which predict that even higher energy products are possible for micromagnetically optimized microstructures.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2022

Entropy Engineering and Tunable Magnetic Order in the Spinel High-Entropy Oxide

Spinel oxides are an ideal setting to explore the interplay between configurational entropy, site selectivity, and magnetism in high-entropy oxides (HEOs). In this work, we characterize the magnetic properties of the spinel (Cr, Mn, Fe, Co, Ni) 3 O 4 and study the evolution of its magnetism as a function of nonmagnetic gallium substitution. Across the range of compositions studied here, from 0 to 40% Ga, magnetic susceptibility and powder neutron diffraction measurements show that ferrimagnetic order is robust in the spinel HEO. However, we also find that the ferrimagnetic order is highly tunable, with the ordering temperature, saturated and sublattice moments, and magnetic hardness all varying significantly as a function of Ga concentration. Through X-ray absorption and magnetic circular dichroism, we are able to correlate this magnetic tunability with strong site selectivity between the various cations and the tetrahedral and octahedral sites in the spinel structure. In particular, we find that while Ni and Cr are largely unaffected by the substitution with Ga, the occupancies of Mn, Co, and Fe are each significantly redistributed. Ga substitution also requires an overall reduction in the transition metal valence, and this is entirely accommodated by Mn. Finally, we show that while site selectivity has an overall suppressing effect on the configurational entropy, over a certain range of compositions, Ga substitution yields a striking increase in the configurational entropy and may confer additional stabilization. In conclusion, spinel oxides can be tuned seamlessly from the low-entropy to the high-entropy regime, making this an ideal platform for entropy engineering.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2016

Colossal thermoelectric power in charge-ordered Li-doped La{sub 0.75}Li{sub 0.25}MnO{sub 3} manganite system

A detail study of transport and magnetic properties of La{sub 1-x}Li{sub x}MnO{sub 3+δ} (0.05 ≤ x ≤ 0.3) system synthesized by wet-chemical mixing route has been done. The room temperature x-ray powder diffraction (XRD) data show single phase behavior of all samples except x = 0.3. Rietveld refinement of XRD data shows structural transition from rhombohedral (R3-C) to orthorhombic (Pnma) symmetry occurs at the Li-doping level x > 0.2 with both the lattice parameter and unit-cell volume decrease with increase of ‘x’. All the samples show ferromagnetic (FM) behavior while metallic behavior are shown by the samples up to Li-concentration x = 0.2. With further Li doping i.e. for x = 0.25, the sample shows insulating behavior accompanied by charge-order transition around T ~ 225 K. Metallic part of the resistivity data of the samples is best fitted with an expression ρ(T) = ρ{sub 0} + ρ{sub 4.5}T{sup 4.5} + C/ sinh{sup 2}(hv{sub s}/2k{sub B}T) containing small-polaron contribution (last term). Most interesting finding in the present study is the observation of large anomalous decrease in thermoelectric power (S) below 100 K shown by the sample with x = 0.25. Probable mechanisms responsible for the observed colossal thermoelectric power have been discussed.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2018

The Effect of Ba Doping on the Structural, Optical, Magnetic, and Dielectric Properties of BiFeO{sub 3} Nanoparticles

Nanoparticles (Nps) of Ba (0, 1 to 5 at.%)-doped BiFeO{sub 3} were synthesized by a sol-gel route at 100 °C using tartaric acid as a chelating agent. The obtained results were studied by using XRD, SEM with EDAX, TEM, UV-vis diffusion reflectance spectra, VSM, and impedance analyzer. EDAX spectra confirmed the presence of Bi, Ba, and Fe in the samples. X-ray diffraction studies showed that BiFeO{sub 3} and Bi{sub 1−x}Ba{sub x}FeO{sub 3} samples exhibited the expected rhombohedral perovskite structure up to a Ba concentration of 3%, whereas 4 and 5% of Ba concentration exhibited the tetragonal phase. TEM studies indicate the particle sizes in the range of 08–28 nm. Reflectance spectra measurements showed a decrease in band gap with increasing Ba concentration. Magnetic properties indicated that the undoped BiFeO{sub 3} and Ba-doped BiFeO{sub 3} samples were ferromagnetic at room temperature. The dielectric constant (ε{sup ′}) and loss (ε{sup ″}) show large dispersion behavior. The dielectric constant increases with an increase of dopant concentration, but a very high value of the dielectric constant was noticed for x = 0.05.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2016

Mechanical and electrical properties of low temperature phase MnBi

Low temperature phase (LTP) manganese bismuth (MnBi) is a promising rare-earth-free permanent magnet material due to its high intrinsic coercivity and large positive temperature coefficient. While scientists are making progress on fabricating bulk MnBi magnets, engineers have begun considering MnBi magnets for motor applications. Physical properties other than magnetic ones could significantly affect motor design. Here, we report results of our investigation on the mechanical and electrical properties of bulk LTP MnBi and their temperature dependence. A MnBi ingot was prepared using an arc melting technique and subsequently underwent grinding, sieving, heat treatment, and cryomilling. The resultant powders with a particle size of ∼5 μm were magnetically aligned, cold pressed, and sintered at a predefined temperature. Micro-hardness testing was performed on a part of original ingot and we found that the hardness of MnBi was 109 ± 15 HV. The sintered magnets were subjected to compressive testing at different temperatures and it was observed that a sintered MnBi magnet fractured when the compressive stress exceeded 193 MPa at room temperature. Impedance spectra were obtained using electrochemical impedance spectroscopy at various temperatures and we found that the electrical resistance of MnBi at room temperature was about 6.85 μΩ m.

Jiang, Xiujuan↗
DOE OSTI2016

Electrical conduction mechanism and improved multiferroic properties of NFO/ (Pb{sub 0.50}Sr{sub 0.50}) TiO{sub 3} bilayer nanostructure composite thin film

Multiferroic 2-2 type layered NFO/ (Pb{sub 0.50}Sr{sub 0.50}) TiO{sub 3} composite thin film on Pt/TiO{sub 2}/Si substrate was prepared by novel metallo-Organic process using spin coating technique. The structural and surface morphology were confirmed by X-Ray diffraction (XRD) atomic force microscope (AFM). Significantly improved ferroelectric properties (P{sub s} ∼ 8.69, P{sub r} ∼ 3.19 µC/cm{sup 2} and E{sub c} ∼ 419kV/cm) and magnetic properties (Ms), (M{sub r}) and (H{sub c}) is (104emu/cc, 0.8emu/cc and 25Oe.) were observed at room temperature. Our observation provides an effective way to manipulate the conduction behavior to understand the leakage current density of multiferroic composites film at the interface. Poole–Frankel tunneling conduction mechanism dominates the leakage current of films in the relatively high electric filed.

71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSIC↗
DOE OSTI2018

Prediction of Half-Metallic Properties in Non-transition Metal-based Binary Compounds X Bi (X = Ba, Sr and Ca) with Zinc-Blende and Wurtzite Structures

In this study, structural, electronic and magnetic properties of non-transition metal-based binary compounds X Bi (X = Ba, Sr and Ca) in five different phases: rock salt, NiAs, wurtzite, zinc blende and CsCl, are investigated in order to find new sp magnetic materials used for real spintronic and other related applications. The calculations are performed by a developed full-potential augmented plane wave plus local orbitals (FP-L/APW + lo) method within the spin density functional theory. As exchange-correlation potential, we used the generalized gradient approximation of Perdew, Burke, and Ernzerhof (GGA-PBE) and the modified Becke-Johnson potential mBJ-GGA-PBE form. It is found that the magnetic moment in these compounds is mainly contributed by the spin-polarized p orbitals of Bi atoms. The WZ XBi are true half-metallic ferromagnet with opposite spin direction at Fermi energy having a magnetic moment of 2.00 μ B per formula unit.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2018

Effect of Barium on Morphological Transition and Magnetic and Dielectric Properties in Ferrite Nanoparticles

Barium ferrite (BaFe{sub 2}O{sub 4}) nanoparticles were synthesized by auto combustion method under different weight percentages of barium. The role of barium in the behavior of spinel ferrite property is identified from this study. XRD exhibits prominent orientation of (212) for BaFe{sub 2}O{sub 4} has confirmed especially in 20 and 30 wt% of barium. The addition of barium metal induced the specific vibration in FTIR spectra and such changes coincide well with the particle size. Further, the EDX spectrum reflects the atomic percentage of elemental presence in the samples of barium ferrite. Addition of barium on ferrite nanoparticles reduces the intensity of fluorescence. The morphological changes occurred due to increasing doping concentration of barium and is visualized from the FESEM and TEM images. The formation of different morphologies such as spherical, hexagonal platelets and small rectangular bar shape are observed only due to inclusion of barium at surfactant medium. The magnetic properties of the barium ferrite samples are studied by VSM. It reveals that 35.11 emu/g saturation magnetization (M{sub s}) with 3775.08 Oe coercivity. The change in values of coercivity (H{sub c}) from 3775.08 to 1572.95 Oe due to the variation of barium levels confirmed that the role of barium induced the hard magnetic behavior. The dielectric study also indicates the significance of barium ferrite in the variation of dielectric constant.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2023

Tuning of the magnetotransport properties of a spin-polarized 2D electron system using visible light

We report on the effects of visible light on the low temperature electronic properties of the spin-polarized two dimensional electron system (2DES) formed at the interfaces between LaAlO 3 , EuTiO 3 and (001) SrTiO 3 . A strong, persistent modulation of both longitudinal and transverse conductivity was obtained using light emitting diodes (LEDs) with emissions at different wavelengths in the visible spectrum range. In particular, Hall effect data show that visible light induces a non-volatile electron filling of bands with mainly 3 dxz,yz character, and at the same time an enhancement of the anomalous Hall effect associated to the magnetic properties of the system. Accordingly, a suppression of the weak-anti localization corrections to the magneto-conductance is found, which correlates with an enhancement of the spin-polarization and of the ferromagnetic character of 2DES. The results establish the LED-induced photo-doping as a viable route for the control of the ground state properties of artificial spin-polarized oxide 2DES.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2016

Near room temperature magnetodielectric consequence in (Li, Ti) doped NiO ceramic

In the quest for high-k dielectrics with decent magnetodielectric (MD) response, ball-milled processed (Li, Ti) doped NiO ceramics have been evaluated by various experimental techniques. Magnetic properties in these ceramics manifest with a pronounced anomaly appearing at ∼260 K, suggesting ferrimagnetic phase (related to cluster magnetism) and co-existence with a glassy-like antiferromagnetic phase at ∼7 K. Room temperature neutron diffraction pattern shows the existence of short-range magnetic correlations. In the magnetically ordered state below 250 K, the magnetic structure is found to be phase coexistence of G-type antiferromagnet and ferrimagnet. Impedance spectroscopy measurements over a wide temperature range can be perfectly described with appropriate microstructural model (internal barrier layer capacitor), based on domain and domain boundary relaxations, justifying the enhancement of the dielectric response. The low-temperature (T < 100 K) dielectric relaxation is polaronic in nature, associated with the charge ordering of a mixed valence states of Ti ions (co-existence of Ti{sup 3+} and Ti{sup 4+}). Finally, our investigations in external magnetic fields up to 15 T reveal the occurrence of negative MD effect near room temperature. This intriguing intrinsic feature has been understood by the mechanism of charge-hopping-mediated MD effects.

71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSIC↗
DOE OSTI2016

Electronic structure of Gd-doped MgO

The electronic structure of Gd-doped MgO is investigated using the LSDA+U (local spin density approximation with U-correction) method and compared with the MgO structure. The total density of states obtained accounting for the correlation effects in the 4f shell of gadolinium is found to be formed by the oxygen 2p states at the valence band and the 4f gadolinium occupied states, while the conduction band is represented by a mixture of empty electronic states. Magnetic properties of the calculated Gd-doped MgO are found to be formed solely by the Gd-4f-magnetic moment of about 7μ{sub B}, in good agreement with recent experimental results suggesting a ferromagnetic coupling of the local magnetic moments induced by Gd.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗