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At least 1,675 records · Page 93
All sourcesNASA NTRSDOE OSTI
DOE OSTI2012

Co-substitution at the Mn-site in YMnO{sub 3}: Structural stability and physical properties

Highlights: Black-Right-Pointing-Pointer Solid state synthesis of several series of hexagonal co-substituted YMn{sub 1-x}(M Prime ,M Double-Prime ){sub x}O{sub 3}. Black-Right-Pointing-Pointer Evidencing the critical parameters which govern the stabilization of the hexagonal phase. Black-Right-Pointing-Pointer Inducing a decrease of the antiferromagnetic ordering temperature by co-substitutions. -- Abstract: The YMnO{sub 3} oxide, crystallizing in the P6{sub 3}cm space group is one of the most studied multiferroic material. While these properties can be modified by substitutions at the Mn-site, the peculiar fivefold coordination appears to limit the M solubility range in YMn{sub 1-x}M{sub x}O{sub 3}. This motivated the preparation by solid state reaction of several series of co-substituted YMn{sub 1-x}(M Prime ,M Double-Prime ){sub x}O{sub 3}, which were studied using both powder X-ray diffraction and transmission electron microscopy. The cation pairs have been chosen for their ability to adopt a fivefold coordination similar to that of Mn{sup 3+} in YMnO{sub 3}, to keep a constant average trivalent oxidation state and to maintain an average cationic radius similar to that of Mn{sup 3+}. For YMn{sub 1-x}(Cu{sub 1/2}Ti{sub 1/2}){sub x}O{sub 3}, a complete solid solution is observed without cation ordering. For all other studied cation pairs, the solubility range is always reaching a minimum value of 25% for the Zn containing pairs (Zn{sub 2/3}V{sub 1/3} and Zn{sub 3/4}Mo{sub 1/4}), a maximum of 50% being reached for the Cu containing pairs (Cu{sub 2/3}V{sub 1/3}, Cu{sub 2/3}Nb{sub 1/3} and Cu{sub 3/4}W{sub 1/4}). Interestingly, the non-centrosymmetric P6{sub 3}cm space group is retained within the solubility range without generating cation ordering phenomena. These co-substitutions at the Mn{sup 3+} are found to induce a decrease of the antiferromagnetic ordering temperature, the T{sub N} variations being similar to the temperature decrease of the dielectric anomaly. Thus, these oxides are interesting candidates for the study of the multiferroic behavior of YMnO{sub 3} derivatives.

36 MATERIALS SCIENCE↗
DOE OSTI2012

Synthesis and characterisation of the novel double perovskites La{sub 2}CrB{sub 2/3}Nb{sub 1/3}O{sub 6}, B = Mg, Ni, Cu

Highlights: ► La{sub 2}CrB{sub 2/3}Nb{sub 1/3}O{sub 6}, B = Mg, Ni, Cu perovskites adopt the GdFeO{sub 3} type structure. ► HREM and ED study indicating week ordering of B-cations for B = Mg. ► Antiferromagnetics with T{sub N} 90 (Mg), 125 (Ni) and 140 K (Ni). -- Abstract: The novel perovskites La{sub 2}CrB{sub 2/3}Nb{sub 1/3}O{sub 6}, B = Mg, Ni, and Cu have been synthesised at 1350 °C in air via the citrate route. Rietveld refinements using neutron powder diffraction (NPD) data showed that the compounds adopt the GdFeO{sub 3} type structure with space group Pbnm, and unit cell parameters a≈b≈√(2)×a{sub p} and c ≈ 2 × a{sub p}, where a{sub p} ≈ 3.8 Å. Selected area electron diffraction (SAED) of B = Ni and Cu samples confirmed space group Pbnm. However, distinct reflections forbidden in Pbnm symmetry, but allowed in the monoclinic sub-group P2{sub 1}/n and unit cell parameters a≈b≈√(2)×a{sub p} and c ≈ 2 × a{sub p}, β ≈ 90° were present in SAED patterns of B = Mg sample. This indicates an ordering of the B-cations within the crystal structure of La{sub 2}CrMg{sub 2/3}Nb{sub 1/3}O{sub 6}. High-resolution electron microscopy (HREM) study indicating uniform, without formation of clusters, ordering of B-cations in the crystallites of La{sub 2}CrMg{sub 2/3}Nb{sub 1/3}O{sub 6}. Magnetic susceptibility measurements show that the compounds are antiferromagnetic (with some glass or spin clustering effects due to additional ferromagnetic interactions between the B-cations) with T{sub N} for La{sub 2}CrB{sub 2/3}Nb{sub 1/3}O{sub 6}, B = Mg, Ni, Cu being 90, 125 and 140 K, respectively.

36 MATERIALS SCIENCE↗
DOE OSTI2012

Structural and magnetic properties of pristine and Fe-doped NiO nanoparticles synthesized by the co-precipitation method

Highlights: ► The prepared samples were characterized by XRD, TEM, HR-TEM techniques. ► Magnetic properties of the samples were compared. ► Surface spins frozen at lower temperatures resulted a spin glass. ► The samples show enhancement of coercivity with decreased temperature. -- Abstract: Ni{sub 1−x}Fe{sub x}O (x = 0 and 0.03) nanoparticles are synthesized by a chemical route. XRD and TEM measurements confirm phase purity and crystallinity of the nanoparticles. Fe substitution in NiO reduces considerably the average particle size of the nanoparticles. The pristine NiO sample with size 14 nm and Fe-substituted sample having size 7 nm show room temperature ferromagnetism. The pristine NiO having 31 nm size and Fe-substituted sample with size 25 nm are found to be antiferromagnetic. The M–H and M–T behavior of the pristine and Fe-doped samples are explained with a core–shell model with an antiferromagnetic core and a ferromagnetic shell. The disordered spins at the shell give rise to a spin-glass like frozen state below 10 K. The obtained room temperature ferromagnetism in the pristine and Fe-doped NiO has been attributed to particle size effect.

36 MATERIALS SCIENCE↗
DOE OSTI2012

Preparation, structural, dielectric and magnetic properties of LaFeO{sub 3}–PbTiO{sub 3} solid solutions

Highlights: ► Solid-solutions of (1−x)LaFeO{sub 3}–(x)PbTiO{sub 3} were synthesized by solid-state reaction. ► XRPD and NPD evidence orthorhombic (x < 0.7) and tetragonal (x > 0.8) crystal structures. ► LaFeO{sub 3}-rich compositions order antiferromagnetically (x < 0.6, G-type structure). ► PbTiO{sub 3}-rich compositions exhibit ferroelectric order (x larger than 0.8). ► Magnetic and dielectric (relaxor) ordering coexist near room-temperature around x = 0.4. -- Abstract: Solid solutions of (1−x)LaFeO{sub 3}–(x)PbTiO{sub 3} (0 < x < 1) have been prepared by conventional solid-state reaction. These complex perovskites have been studied by means of X-ray (XRPD) and neutron powder (NPD) diffraction, complemented with dielectric, magnetic, heat capacity and Mössbauer measurements. Complete solubility in the perovskite series was demonstrated. The NPD and XRPD patterns were successfully refined as orthorhombic (x ≤ 0.7) and tetragonal (x ≥ 0.8). A composition-driven phase transformation occurs within the interval 0.7 < x < 0.8. The samples with x < 0.5 showed evidence of long-range magnetic ordering with an G-type antiferromagnetic arrangement of the magnetic moments of the Fe{sup 3+} cations in the B-site with propagation vector k = (0,0,0). Based on the obtained experimental data, a combined structural and magnetic phase diagram has been constructed. The factors governing the structural, dielectric and magnetic properties of (1−x)LaFeO{sub 3}–(x)PbTiO{sub 3} solid solutions are discussed, as well as their possible multiferroicity.

36 MATERIALS SCIENCE↗
DOE OSTI2013

Microstructures, magnetic and electric properties of diluted magnetic semiconductors InTe{sub 1−x} Fe{sub x} (Co{sub x})

Highlights: ► The prepared InTe{sub 0.9}Fe{sub 0.1} was found to be ferromagnetic at room temperature and can be characterized as diluted magnetic semiconductors. ► The presence of staking faults, various types of defects, strained lattice, grain boundaries and the impurity of minor non-magnetic phase were suggested to participate in high temperature ferromagnetism. - Abstract: InTe compound doped by 10% of Fe or Co respectively was synthesized. X-ray diffraction (XRD), transmission electron microscope (TEM), scanning electron microscope (SEM), energy dispersive X-ray (EDX), vibrating sample magnetometer (VSM) and Kiethley electrometer were used for characterizing the prepared samples. XRD show the presence of InTe{sub 0.9}Fe{sub 0.1} or InTe{sub 0.9}Co{sub 0.1} together with minor In{sub 4}Te{sub 3} phase. InTe{sub 0.9}Fe{sub 0.1} is ferromagnetic with high Curie and high blocking temperature, while InTe{sub 0.9}Co{sub 0.1} is antiferromagnetic with two high Neels temperatures. σRT of InTe{sub 0.9}Fe{sub 0.1} and InTe{sub 0.9}Co{sub 0.1} are greater than those of InTe. The higher conductivity is due to the higher carrier's density obtained from the interaction of the sp-d orbitals, of the electric and magnetic system. The presence of In{sub 4}Te{sub 3} minor phase and different kinds of defects are taking major roles in the formation of high Tc ferromagnetism and antiferromagnetism.

36 MATERIALS SCIENCE↗
DOE OSTI2013

Synthesis, magnetic and dielectric characterization of nanocrystalline solid solutions of In{sub 2−x}Ni{sub x}O{sub 3} (x = 0.05, 0.10 and 0.15)

Graphical abstract: Monophasic and crystalline In{sub 2−x}Ni{sub x}O{sub 3} nanoparticles of size 8–15 nm have been synthesized solvothermally and showed red shift in energy band gap which decreases on increasing Ni{sup 2+} concentration in In{sub 2}O{sub 3} host lattice. - Highlights: • Monophasic Ni-doped In{sub 2}O{sub 3} nanoparticles by solvothermal method for first time. • Plausible reaction mechanism using thermogravimetric analysis. • High surface area with small particle size obtained. • Solid solutions exhibit paramagnetism with very weak antiferromagnetic interactions. - Abstract: In{sub 2−x}Ni{sub x}O{sub 3} (x = 0.05, 0.10 and 0.15) nanoparticles were successfully synthesized by solvothermal method by the thermal decomposition of oxalate precursor at 450 °C for the first time. X-ray diffraction studies showed the formation of highly crystalline and monophasic cubic structure of In{sub 2}O{sub 3} which is attributed to the formation of solid solution. These nanoparticles show good optical transmittance in the visible region. Optical measurements showed an energy band gap which decreases with increasing Ni concentration. The grain size decreases from 15 nm to 8 nm and surface area increases from 90 to 254 m{sup 2} g{sup −1} on increasing the Ni concentration. High dielectric constant and dielectric loss has been obtained which indicates the conducting nature of these solid solutions. Magnetic measurements showed that the samples are strong paramagnetic in nature with very weak antiferromagnetic interactions. No evidence of ferromagnetism is observed for these solid solutions at room temperature.

36 MATERIALS SCIENCE↗
DOE OSTI2013

Structural and magnetic properties of Sm{sub 2−x}Mn{sub x}O{sub 3} nanoparticles

Graphical abstract: - Highlights: • C-type Sm{sub 2−x}Mn{sub x}O{sub 3} (0.0 ≤ x ≤0.20) is prepared by sol–gel method. • A maximum solubility of x = 0.15 is confirmed by X-ray diffraction, Raman and infrared techniques. • Samples with x > 0.05 exhibit weak ferromagnetic properties; for x ≤ 0.05 antiferromagnetic behaviors is obtained. • Correlation between magnetic behaviors and structural and microstructural parameters is discussed. - Abstract: Mixed oxide Sm{sub 2−x}Mn{sub x}O{sub 3} (SMO), x = 0.0, 0.05, 0.10, 0.15 and 0.20 were synthesized by a sol–gel process. A single phase solid solution is formed up to x = 0.15 which confirmed by using X-ray diffraction, Raman spectroscopy and infrared techniques. Crystal structure and microstructure analyses were performed by Rietveld refinement. Preferential cationic distribution, over the two crystallographic sites 8b and 24d of space group Ia3{sup ¯}, is found for doped samples but with different extent. The r.m.s. microstrain 〈ε{sub L}{sup 2}〉{sup 1/2} depends on composition x in a systematic way emphasizing the preferential distribution. Magnetization measurements show that samples with x ≤ 0.05 have antiferromagnetic behavior, while samples with x > 0.05 exhibit a weak ferromagnetic behavior with magnetic phase transformation at 15 and 16 K for x = 0.1 and x = 0.15, respectively.

36 MATERIALS SCIENCE↗
DOE OSTI2014

Investigation of nanocrystalline zinc chromite obtained by two soft chemical routes

Graphical abstract: - Highlights: • Two soft chemical routes to synthesize zinc chromites are described. • Glycine is used as chelating agent (precursor method) and fuel (solution combustion method). • The synthesized chromites have crystallite size in the range of 18–27 nm. • An antiferromagnetic (AFM) transition is observed at about T{sub N} ∼ 18 K. - Abstract: Zinc chromite (ZnCr{sub 2}O{sub 4}) nanocrystalline powders were obtained by two different chemical routes: the precursor method and the solution combustion method involving glycine-nitrates. The complex compound precursors, [ZnCr{sub 2}(NH{sub 2}CH{sub 2}COO){sub 8}]·9H{sub 2}O and [ZnCr{sub 2}(NH{sub 2}CH{sub 2}COOH){sub 4.5}]·(NO{sub 3}){sub 8}·6H{sub 2}O, were characterized by chemical analysis, infrared spectroscopy (IR), ultraviolet–visible spectroscopy (UV–vis) and thermal analysis. The structure, morphology, surface chemistry and magnetic properties of ZnCr{sub 2}O{sub 4} powders were investigated by X-ray diffraction (XRD), scanning electron microscopy (SEM), X-ray photoelectron spectroscopy (XPS), infrared and Raman spectroscopy (RS), ultraviolet–visible spectroscopy (UV–vis) and magnetic measurements. X-ray diffraction patterns indicated the chromite spinel phase with good crystallinity and an average crystallite size of approximately 18–27 nm. The band gap values ranged between 3.31 and 3.33 eV. The magnetic measurements indicated an antiferromagnetic transition at T{sub N} ∼ 17.5/18 K.

36 MATERIALS SCIENCE↗
DOE OSTI2014

Anisotropic lattice thermal expansion of PbFeBO{sub 4}: A study by X-ray and neutron diffraction, Raman spectroscopy and DFT calculations

Highlights: • Mullite-type PbFeBO{sub 4} shows uni-axial negative coefficient of thermal expansion. • Anisotropic thermal expansion of the metric parameters was modeled using modified Grüneisen approximation. • The model includes harmonic, quasi-harmonic and intrinsic anharmonic contributions to the internal energy. • DFT calculation, temperature- and pressure-dependent Raman spectra help understand the phonon decay and associated anharmonicity. - Abstract: The lattice thermal expansion of mullite-type PbFeBO{sub 4} is presented in this study. The thermal expansion coefficients of the metric parameters were obtained from composite data collected from temperature-dependent neutron and X-ray powder diffraction between 10 K and 700 K. The volume thermal expansion was modeled using extended Grüneisen first-order approximation to the zero-pressure equation of state. The additive frame of the model includes harmonic, quasi-harmonic and intrinsic anharmonic potentials to describe the change of the internal energy as a function of temperature. The unit-cell volume at zero-pressure and 0 K was optimized during the DFT simulations. Harmonic frequencies of the optical Raman modes at the Γ-point of the Brillouin zone at 0 K were also calculated by DFT, which help to assign and crosscheck the experimental frequencies. The low-temperature Raman spectra showed significant anomaly in the antiferromagnetic regions, leading to softening or hardening of some phonons. Selected modes were analyzed using a modified Klemens model. The shift of the frequencies and the broadening of the line-widths helped to understand the anharmonic vibrational behaviors of the PbO{sub 4}, FeO{sub 6} and BO{sub 3} polyhedra as a function of temperature.

36 MATERIALS SCIENCE↗
DOE OSTI2016

Zn{sub 1−x}Co{sub x}WO{sub 4} (0 ≤ x ≤ 1) full range solid solution: Structure, optical properties, and magnetism

Graphical abstract: The continuous modulation on crystal structure and band gap is achieved in the Zn{sub 1−x}Co{sub x}WO{sub 4} (0 ≤ x ≤ 1) full range solid solution. - Highlights: • Zn{sub 1−x}Co{sub x}WO{sub 4} (0 ≤ x ≤ 1) solid solution was synthesized by a hydrothermal method. • They all present a single-phase in the wolframite structure with space group P2/c. • The continuous tenability in band gap was achieved in Zn{sub 1−x}Co{sub x}WO{sub 4} (0 ≤ x ≤ 1). • CoWO{sub 4} and Zn{sub 0.5}Co{sub 0.5}WO{sub 4} are antiferromagnetic and paramagnetic, respectively. - Abstract: A novel full-range solid-solution Zn{sub 1−x}Co{sub x}WO{sub 4} (0 ≤ x ≤ 1) was successfully developed via a facile one-pot hydrothermal route. The phase structure and microstructure were characterized by X-ray diffraction (XRD), Fourier-transform infrared (FTIR) spectra and scanning electron microscopy (SEM). The Zn{sub 1−x}Co{sub x}WO{sub 4} solid solution possesses similar wolframite crystal structure with the same space group P2/c. Diffuse reflection spectroscopy (DRS) measurements on Zn{sub 1−x}Co{sub x}WO{sub 4} (0 ≤ x ≤ 1) demonstrated that the optical band gap can be continuously tuned from 3.56 eV to 2.61 eV for direct transition and 1.87 eV for indirect transition, respectively, with increasing x from 0 to 1. Magnetic susceptibility measurements reveal that CoWO{sub 4} has an antiferromagnetic transition at T{sub N} = 42 K, whereas Zn{sub 0.5}Co{sub 0.5}WO{sub 4} exhibits paramagnetic behavior. Moreover, CoWO{sub 4} and Zn{sub 0.5}Co{sub 0.5}WO{sub 4} obey the Curie–Weiss law from 200 k down to 50 K, and their effective magnetic moments were determined.

36 MATERIALS SCIENCE↗
DOE OSTI2016

Polarons induced electronic transport, dielectric relaxation and magnetodielectric coupling in spin frustrated Ba{sub 2}FeWO{sub 6}

Highlights: • Ordered double perovskite Ba{sub 2}FeWO{sub 6} synthesized in reducing atmosphere possess a tetragonal I4/m crystal structure with mixed valent Fe/W cations. • Ba{sub 2}FeWO{sub 6} has an antiferromagnetic structure with T{sub N} at 19 K. • Insulating Ba{sub 2}FeWO{sub 6} shows different conducting mechanisms at different temperature regions and dielectric relaxation. • The polarons invoked by the mixed valence state of cations and their disordered arrangements are solely responsible for the various physical phenomena observed in Ba{sub 2}FeWO{sub 6}. - Abstract: Mixed valent double perovskite Ba{sub 2}FeWO{sub 6}, with tetragonal crystal structure, synthesized in a highly controlled reducing atmosphere, shows antiferromagnetic transition at T{sub N} = 19 K. A cluster glass-like transition is observed around 30 K arising from the competing interactions between inhomogeneous magnetic states. The structural distortion leads to the formation of polarons that are not contributing to DC conduction below charge ordering temperature, T{sub CO} = 279 K. Above T{sub CO}, small polarons will start to hop by exploiting thermal energy and participate in the conduction mechanism. The polarons are also responsible for the dielectric relaxor behavior, in which the dielectric relaxation time follows non-linearity in temperature as proposed by Fulcher. The material also exhibits a small room temperature magnetoresistance of 1.7% at 90 kOe. An intrinsic magnetodielectric coupling of ∼4% near room temperature and at lower temperatures, as well as an extrinsic magnetodielectric coupling change from +4% to −6% at around 210 K are reported.

36 MATERIALS SCIENCE↗
DOE OSTI2016

Correlating melting and collapse of charge ordering with magnetic transitions in La{sub 0.5-x}Pr{sub x}Ca{sub 0.5}MnO{sub 3}

Highlights: • Concept of normalized magnetization is introduced to explain relative magnetic transitions. • Coexistence of two magnetic modes is correlated with the magnetic transitions and MIT. • Field induced melting and collapse of charge ordered antiferromagnetic (CO-AFM) state into ferromagnetic (FM) state is conferred. - Abstract: The magnetic properties of polycrystalline La{sub 0.5-x}Pr{sub x}Ca{sub 0.5}MnO{sub 3} material are investigated at different temperatures. The existence of magnetically diverse phases associated with various relaxation modes and their modulation with temperature and doping is analyzed. La{sub 0.5}Ca{sub 0.5}MnO{sub 3} exhibited field induced melting and collapse of charge ordered antiferromagnetic (CO-AFM) phase into ferromagnetic (FM) state. This phenomenon results in lowering of Neel’s temperature (T{sub N}) along with changes in the slope of magnetic moment with temperature. Using normalized M(T) curves, the variation and interplay of charge ordered temperature (T{sub CO}), Curie temperature (T{sub C}) and T{sub N} is conferred. The coexistence of two magnetic modes is explained as major ingredient for the magnetic transitions as well as metal to insulator transition (MIT); where melting and collapse of charge ordering is conversed as basic feature in these Praseodymium (Pr) doped La{sub 0.5}Ca{sub 0.5}MnO{sub 3} materials.

36 MATERIALS SCIENCE↗
DOE OSTI2018

Cr3 Triangles induced competing magnetic interactions in the new metal boride TiCrIr2B2: An NMR and DFT study

Highlights: • One-dimensional trigonal arrangements of chromium atoms (Cr{sub 3}) was found in TiCrIr{sub 2}B{sub 2}. • Competing weak ferromagnetic and strong antiferromagnetic interactions support an itinerant d-band character for TiCrIr{sub 2}B{sub 2}. • Spin-polarized and non-spin-polarized DOS results for TiCrIr{sub 2}B{sub 2} unveil an electronic instability and the presence of a pseudogap at E{sub F}, respectively. - Abstract: The presence of one-dimensional trigonal arrangements of chromium atoms (Cr{sub 3}) in the structure of TiCrIr{sub 2}B{sub 2} leads to a magnetic transition near ambient temperature. Herein we report an investigation of the nature of electronic and magnetic properties of TiCrIr{sub 2}B{sub 2} via ab initio calculations together with {sup 11}B NMR Knight shift (K) and spin-lattice relaxation rate (1/T{sub 1}) analysis. The presence of a characteristic rectangular powder pattern below 280 K, absence of a Korringa relation, strong enhancement of 1/T{sub 1}.T at low temperatures and weak temperature dependence of K indicate competition between antiferromagnetic and ferromagnetic spin fluctuations in the itinerant d-band electrons, in agreement with ab initio calculations. One-dimensional trigonal arrangements of magnetically active elements in intermetallic compounds, as is found in TiCrIr{sub 2}B{sub 2}, are quite rare and could lead to exotic phenomena such as spin-chirality and quantum criticality in low-dimensional frustrated lattices.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2018

Effect of BiFeO3 nanoparticle on electrical, thermal and magnetic properties of polyvinyl alcohol (PVA) composite film

Highlights: • Conductivity increases with increasing of BFO in PVA nanocomposite. • The resistivity of the films increases with lowering temperature. • Characteristic relaxation time increases with BFO contents in composites. • The Current-voltage characteristics of the film samples show nonlinearity. • A transformation from antiferromagnetic to diamagnetic behaviour is observed. - Abstract: Synthesis of BiFeO{sub 3} (BFO) nanoparticles (NPs) is demonstrated by sol-gel method. The fabrication of the flexible nanocomposite films based on different wt. % of BFO NPs and Polyvinyl alcohol (PVA) has been done by solution casting method. Conductivity as well as thermal stability tends to increase with the increase in wt. % of BFO filler in PVA matrix. Current-voltage characteristics of the composite films show nonlinearity which invokes the concept of back to back Schottky diode. Due to generation of recombination current and high leakage current, large value of ideality factor arises in the BFO-PVA nanocomposite film. Activation energies from dc conductivity and dielectric response have been evaluated and a decreasing trend in activation energy is observed with the increase in wt. % of BFO nanoparticle insertion in the PVA matrix. At room temperature, BFO NPs exhibit antiferromagnetic behaviour whereas BFO-PVA composite films show diamagnetism.

77 NANOSCIENCE AND NANOTECHNOLOGY↗
DOE OSTI2018

Synthesis and magnetic properties of nanocrystalline Gd3Fe5O12 and GdFeO3 powders prepared by sol–gel auto-combustion method

Highlights: • Glycine-based gel was successfully applied in the preparation of Gd ferrites. • High-purity nanocrystalline Gd{sub 3}Fe{sub 5}O{sub 12} and GdFeO{sub 3} powders were synthesized. • Magnetic properties of nanocrystalline GdFeO{sub 3} and Gd{sub 3}Fe{sub 5}O{sub 12} were investigated. • Transition mechanism of magnetic phase was discussed in detail. - Abstract: Nanocrystalline GdFeO{sub 3} and Gd{sub 3}Fe{sub 5}O{sub 12} powders were prepared successfully by sol–gel auto-combustion method using a glycine-based gel. The as-prepared GdFeO{sub 3} and Gd{sub 3}Fe{sub 5}O{sub 12} powders presented spherical shape, and composed of continuous porous network structure due to the releasing of a large amount of gases during auto-combustion process. This special microstructure was significant for reducing the magnetic interactions between nanocrystalline powders. The Gd{sub 3}Fe{sub 5}O{sub 12} samples presented ferrimagnetic feature at low temperatures. At 10 K, the saturate magnetization is about 87.9 emu/g. As temperature increased to 300 K, the magnetization decreased rapidly since the thermal fluctuations changed the main magnetic spin ordering. The GdFeO{sub 3} samples presented antiferromagnetic feature at 5 K, and the magnetization reaches 109 emu/g at 50,000 Oe field. As temperature increased to 300 K, the antiferromagnetism decreased rapidly, and the magnetization curve presents linear tendency due to the dominant paramagnetism contribution of Gd{sup 3+} ions.

77 NANOSCIENCE AND NANOTECHNOLOGY↗
DOE OSTI2018

Anisotropic magnetic properties of the triangular plane lattice material TmMgGaO4

Highlights: • TmMgGaO{sub 4} crystallizes in the R-3m space group with the YbFe{sub 2}O{sub 4} structure. • TmMgGaO{sub 4} exhibits geometric magnetic frustration with no ordering down to 1.8 K. • Magnetic properties of TmMgGaO{sub 4} are highly anisotropic. - Abstract: The crystal growth, structure, and basic magnetic properties of TmMgGaO{sub 4} are reported. The Tm ions are located in a planar triangular lattice consisting of distorted TmO{sub 6} octahedra, while the Mg and Ga atoms randomly occupy intermediary bilayers of M-O triangular bipyramids. The Tm ions are positionally disordered. The material displays an antiferromagnetic Curie Weiss theta of ∼−20 −25 K, with no clear ordering visible in the magnetic susceptibility down to 1.8 K; the structure and magnetic properties suggest that ordering of the magnetic moments is frustrated by both structural disorder and the triangular magnetic motif. Single crystal magnetization measurements indicate that the magnetic properties are highly anisotropic, with large moments measured perpendicular to the triangular planes. At 2 K, a broad step-like feature is seen in the field-dependent magnetization perpendicular to the plane on applied field near 2 T.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2018

Magnetic structure of CaSrFeCoO6–δ: Correlations with structural order

Highlights: • Neutron diffraction shows that CaSrFeCoO{sub 6–δ} has G-type antiferromagnetic order at 10 K. • Magnetic moments are along the shortest axis at 10 K, contrary to the Ca{sub 2}-analogue, Ca{sub 2}FeCoO{sub 6–δ}. • CaSrFeCoO{sub 6–δ} retains the same orientation of moments up to 300 K, contrary to Ca{sub 2}FeCoO{sub 6–δ}. • CaSrFeCoO{sub 6–δ} has the optimum composition for G-type order and retention of the moment orientation. - Abstract: With the aid of neutron diffraction, the magnetic structure of CaSrFeCoO{sub 6–δ} is determined at 10 K and 300 K. The vacancies, created due to oxygen-deficiency, are ordered in this material. In addition to structural order, neutron diffraction shows a long-range G-type antiferromagnetic order, where each magnetic moment is aligned antiparallel to all nearest neighbors. The orientation of moments is along the shortest unit cell axis at 10 K. The magnetic structure and orientation of moments remain unchanged up to room temperature. This is in contrast to the Ca{sub 2}-analogue, Ca{sub 2}FeCoO{sub 6–δ}, where the magnetic moments at 10 K are parallel to the longest axis and change their orientation when temperature is raised to room temperature. These differences highlight the ability to control the magnetic properties by tuning the structural parameters. Comparisons to similar materials show that CaSrFeCoO{sub 6–δ} has the optimum composition for G-type magnetic order and the retention of the moment orientation.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2018

The synthesis of CuO and NiO nanoparticles by facile thermal decomposition of metal-Schiff base complexes and an examination of their electric, thermoelectric and magnetic Properties

Highlights: • Thermal decomposition of Schiff base complexes provides a convenient and effective pathway to fabricate CuO and NiO NPs. • The electrical conduction in CuO NPs and NiO NPs is governed by intrinsic band-to-band type and large polarons conduction mechanism, respectively. • The thermoelectric measurements confirm that the NPs are P-type degenerate semiconductors. • The NPs show weak ferromagnetic ordering at room temperature and antiferromagnetic to paramagnetic transition with high dipolar interaction. - Abstract: In this study, CuO and NiO NPs have been synthesized by facile thermal decomposition of Schiff base complexes and their physical properties have been examined. The synthesized CuO and NiO NPs are crystallized in polycrystalline monoclinic and cubic structures with average particle size 17 ± 0.4 and 62 ± 1 nm, respectively. The electrical conductivity measurements confirm that the conduction in the CuO NPs is a band-to-band type while the conduction in the NiO NPs is governed by the large polaron conduction mechanism. The thermoelectric measurements confirm that the CuO and NiO NPs are P-type degenerate semiconductors with room temperature Seebeck coefficients equal to 89.9 and 12.1 mV/K, respectively. The magnetic measurements exhibit that the NPs have weak ferromagnetic ordering and antiferromagnetic to paramagnetic transition with high dipolar interaction.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗