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DOE OSTI2025

AC electrical transport detection of magnetic properties of small, granular, and heterogeneous samples

Experimental constraints and sample limitations can preclude ideal measurements of electrical transport properties of materials. In such situations, AC electrical transport methods are often employed due to a significant increase in signal-to-noise ratio they can provide. However, dynamic effects that are not often accounted for may be present that may modify the signals in these measurements. In particular, dynamic filtering effects are prominent in small, granular, and heterogeneous materials. We demonstrate that a lock-in amplifier based circuit can distinguish between these DC transport and AC filtering effects. Here, we further demonstrate that this filtering can reveal distinct signatures of magnetic transitions while providing a measure of sample quality.

47 OTHER INSTRUMENTATION↗

DOE OSTI2023

Structural, electronic, and magnetic properties of CoFeVGe-based compounds: Experiment and theory

We have carried out a combined theoretical and experimental investigation of both stoichiometric and nonstoichiometric CoFeVGe alloys. In particular, we have investigated CoFeVGe, Co 1.25 Fe 0.75 VGe, Co 0.75 Fe 1.25 VGe, and CoFe 0.75 VGe bulk alloys. Our first principles calculations suggest that all four alloys show ferromagnetic order, where CoFeVGe, Co 1.25 Fe 0.75 VGe, and Co 0.75 Fe 1.25 VGe are highly spin polarized with spin polarization values of over 80%. However, the spin polarization value of CoFe 0.75 VGe is only about 60%. We have synthesized all four samples using arc melting and high-vacuum annealing at 600 °C for 48 hours. The room temperature x-ray diffraction of these samples exhibits a cubic crystal structure with disorder. All the samples show single magnetic transitions at their Curie temperatures, where the Curie temperature and high field (3T) magnetization are 288 K and 42 emu/g; 305 K and 1.5 emu/g; 238 K and 39 emu/g; and 306 K and 35 emu/g for CoFeVGe, Co 1.25 Fe 0.75 VGe, Co 0.75 Fe 1.25 VGe, and CoFe 0.75 VGe, respectively.

36 MATERIALS SCIENCE↗

DOE OSTI2024

Influence of Ga doping on magnetic properties, magnetocaloric effect, and electronic structure of pseudobinary GdZn 1 - x Ga x ( x = 0 - 0.1 )

Here, we explore the impact of introducing IIIA-group element Ga in place of IIB-group element Zn in binary intermetallic GdZn on its magnetic and magnetocaloric properties, as well as explicate the modified electronic band structure of the compound. The magnetic transition temperature of the compound decreases with the increase of Ga concentration in GdZn 1-x ⁢Ga x ⁢(x = 0–0.1) while the crystal structure (CsCl prototype) and lattice parameters remain unchanged. Our detailed analysis of magnetization and magnetocaloric data conclusively proves that long-ranged magnetic ordering exists in the sample, despite the magnetic interaction considerably weakening with the increase of Ga. The experimental data are rationalized using both a theoretical machine-learning model and first-principle density functional theory. The electronic band structure of GdZn is manifested with some unusual complex features which gradually diminish with Ga doping and the conventional sinusoidal feature of Ruderman-Kittel-Kasuya-Yosida-type interactions also disappears. A mean-field theory model is developed and can successfully describe the overall magnetocaloric behavior of the GdZn 1-x⁢ Ga x series of samples.

36 MATERIALS SCIENCE↗

DOE OSTI2016

Structural chemistry and magnetic properties of the perovskite Sr{sub 3}Fe{sub 2}TeO{sub 9}

A polycrystalline sample of perovskite-like Sr{sub 3}Fe{sub 2}TeO{sub 9} has been prepared in a solid-state reaction and studied by a combination of electron microscopy, Mössbauer spectroscopy, magnetometry, X-ray diffraction and neutron diffraction. The majority of the reaction product is shown to be a trigonal phase with a 2:1 ordered arrangement of Fe{sup 3+} and Te{sup 6+} cations. However, the sample is prone to nano-twinning and tetragonal domains with a different pattern of cation ordering exist within many crystallites. Antiferromagnetic ordering exists in the trigonal phase at 300 K and Sr{sub 3}Fe{sub 2}TeO{sub 9} is thus the first example of a perovskite with 2:1 trigonal cation ordering to show long-range magnetic order. At 300 K the antiferromagnetic phase coexists with two paramagnetic phases which show spin-glass behaviour below ~80 K. - Graphical abstract: Sr{sub 3}Fe{sub 2}TeO{sub 9} has a 2:1 ordered arrangement of Fe{sup 3+} and Te{sup 6+} cations over the octahedral sites of a perovskite structure and is antiferromagnetic at room temperature. - Highlights: • 2:1 Cation ordering in a trigonal perovskite. • Magnetically ordered trigonal perovskite. • Intergrowth of nanodomains in perovskite microstructure.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗

DOE OSTI2019

Spin Polarization and Magnetic Properties of V{sub Ga}O{sub N} and V{sub Ga}O{sub N}In{sub Ga} in GaN: GGA+U Approach

Electronic structure of a defect center containing the gallium vacancy and substitutional oxygen atom at nitrogen site (V{sub Ga}O{sub N}) in zinc blende and wurtzite GaN was analyzed within GGA+U approach. The +U term was applied to d(Ga), p(N), p(O), and d(In). Neutral V{sub Ga}O{sub N} is in the stable high spin state with spin S = 1. The defect structure is strongly dependent on geometry of the defect and the charge state. Two spin structures, which arise due to two different configurations in V{sub Ga}O{sub N}, with O{sub N} either along the c-axis or in one of three equivalent tetrahedral positions in wurtzite structure were analyzed. The weak ferromagnetic coupling between centers was found. The strength of magnetic coupling is increased when there is a complex containing V{sub Ga}O{sub N} with additional substitutional indium atom at the second neighbor to vacancy gallium site (V{sub Ga}O{sub N}In{sub Ga}). Magnetic coupling between V{sub Ga}O{sub N}In{sub Ga} is ferromagnetic due to strong spin polarization of p electrons of the nearest and distant nitrogen atoms.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗

DOE OSTI2019

Structural and Magnetic Properties of FePt/SiO{sub 2} Core/Shell Nanoparticles

The disorder-order phase transition of FePt/SiO{sub 2} core/shell nanoparticles (NPs) induced by rapid thermal annealing was investigated. The FePt/SiO{sub 2} NPs were synthesized using FePt cores as seeds. For as-prepared FePt/SiO{sub 2} NPs, the average size of the FePt core and the thickness of the SiO{sub 2} shell are about 4.8 and 1.2 nm respectively, and the FePt NPs exhibit a disordered fcc structure. The FePt core NPs show obvious phase transformation from a disordered to an ordered structure after they were annealed at 600 °C for 2 min. Moreover, increasing annealing time can promote effectively the formation of the ordered fct-FePt phase. The relatively large coercivity H{sub c} is obtained for FePt NPs with a thicker SiO{sub 2} shell. The H{sub c} decreases firstly with decreasing temperature from 300 to 100 K and then increases from 100 to 10 K, which is ascribed to the coexistence of magnetically hard fct-FePt and magnetically soft fcc-FePt in the sample, and the incomplete exchange coupling between the hard and soft magnetic phases.

77 NANOSCIENCE AND NANOTECHNOLOGY↗

DOE OSTI2018

Investigation of Substitution of Cu and Se Atoms on the Electronic and Magnetic Properties of GaN Monolayer Nanosheet

In this paper, some of the electronic properties of GaN monolayer nanosheet are investigated in its pure form and after substitution of Cu and Se atoms. Electronic properties have been calculated based on the density functional theory approach with full-potential linearized augmented plane wave method. The results show that GaN nanosheet is a nonmagnetic semiconductor and its energy gap is equal to 2.202 eV. Our results show that GaN nanosheet properties vary with substitution of Cu or Se atoms: GaSeN and GaCuN show half-metallic and metallic behaviors, respectively. Calculated magnetic moments for GaSeN and GaCuN are 1.00 and 1.127 µ{sub B}, respectively.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗

DOE OSTI2019

Synthesis, structure and magnetic properties of Ba 3 M 2 Ge 4 O 14 (M = Mn and Fe): Quasi-one-dimensional zigzag chain compounds

A series of trivalent transition metal germanates with a general formula of A 3 M 2 Ge 4 O 14 ( A = Sr, Ba, M = Mn and Fe) was synthesized using a high-temperature (580 °C) hydrothermal technique. Compound I , Ba 3 Mn 2 Ge 4 O 14 , is a new structure type that is characterized by one-dimensional Mn–O–Mn chains made from edge-sharing highly distorted Mn 3+ O 6 units, and exhibits antiferromagnetic behavior below 15 K with field induced metamagnetic transitions. The A 3 Fe 2 Ge 4 O 14 ( A = Sr and Ba, II and III, respectively) series belongs to the well-known langasite structure type, crystallizing in space group P 321. In A 3 Fe 2 Ge 4 O 14 , there is one octahedral Fe 3+ site and one mixed-occupancy Fe 3+ /Ge 4+ site that form the one-dimensional substructure. The magnetic susceptibility data of Ba 3 Fe 2 Ge 4 O 14 reveals a much simpler magnetic structure with an antiferromagnetic transition near 5.5 K. The Jahn-Teller distortion of Mn 3+ appears to be influential in the phase formation, leading to significantly different structures for these Mn 3+ and Fe 3+ compounds with similar chemical formulas.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗

DOE OSTI2017

Magnetic properties of the 6H perovskite Ba{sub 3}Fe{sub 2}TeO{sub 9}

A polycrystalline sample of Ba{sub 3}Fe{sub 2}TeO{sub 9} having the 6H perovskite structure has been prepared in a solid-state reaction and studied by a combination of electron microscopy, Mössbauer spectroscopy, magnetometry, X-ray diffraction and neutron diffraction. Partial ordering of Fe{sup 3+} and Te{sup 6+} cations occurs over the six-coordinate sites; the corner-sharing octahedra are predominantly occupied by the former and the face-sharing octahedra by a 1:1 mixture of the two. On cooling through the temperature range 18 < T/K < 295 an increasing number of spins join an antiferromagnetic backbone running through the structure while the remainder show complex relaxation effects. At 3 K an antiferromagnetic phase and a spin glass coexist. - Graphical abstract: On cooling an increasing number of spins join an antiferromagnetic backbone running through the structure while the remainder show complex relaxation effects. Display Omitted - Highlights: • Rapid spin relaxation occurs over a wide temperature range below the Néel temperature. • Magnetic moments on two cation sublattices develop at significantly different rates. • Centrosymmetric structure is confirmed by electron microscopy.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗

DOE OSTI2019

Structural, Bulk Permittivity, and Magnetic Properties of Lead-Free Electronic Material: Ba{sub 1}Bi{sub 1}Cu{sub 1}Fe{sub 1}Ni{sub 1}Ti{sub 3}O{sub 12}

In this report, Ba{sub 1}Bi{sub 1}Cu{sub 1}Fe{sub 1}Ni{sub 1}Ti{sub 3}O{sub 12} (BBCFNTO termed further) ceramics were synthesized using a conventional ceramic processing route. The formation of multiple phases has been confirmed from by the XRD pattern at room temperature. The surface micrograph indicates the uniform distribution of grains with distinct grain boundary. The co-relation between the impedance and dielectric parameters was realized by using a phase sensitive meter over a good temperature and frequency range. The temperature- and frequency-dependent dielectric properties are linked to the conduction mechanism. The dielectric constant (K) and loss (tanδ) are increased sharply at high-temperature region, which is expected to be the onset of dipolar relaxation phenomena. The contribution of grain boundary (GBs) and grain (Gs) effects can be identified using the complex impedance spectroscopy. This synthesized material is investigated to model multifunctional devices.

36 MATERIALS SCIENCE↗

DOE OSTI2018

Temperature-Dependent Magnetic Properties of Electrodeposited CoPtP Alloy Nanowires

CoPtP alloy nanowires, ~ 200 nm in diameter, have been prepared by the electrodeposition method into the pores of a porous anodic aluminum oxide template. X-ray diffraction pattern shows that the wires consist of a mixture of fcc and hcp phases with CoPt (002) and CoPt (221) texture. The coercivity was found to be 1150 Oe at 50 K and 760 Oe at 300 K, when the field was applied parallel to the wire axis. The temperature dependence of coercivity was explained by considering the magnetocrystalline anisotropy and thermal activation effect.

77 NANOSCIENCE AND NANOTECHNOLOGY↗

DOE OSTI2024

Emergence of the isotropic Kitaev honeycomb lattice $α$–RuCl 3 and its magnetic properties

Here, we present a comprehensive investigation of the crystal and magnetic structures of the van der Waals antiferromagnet $α$–RuCl 3 using single crystal x-ray and neutron diffraction. The crystal structure at room temperature is a monoclinic (C2/m). However, with decreasing temperature, a remarkable first-order structural phase transition is observed, leading to the emergence of a rhombohedral ($R\bar3$) structure characterized by three-fold rotational symmetry forming an isotropic honeycomb lattice. On further cooling, a zigzag-type antiferromagnetic order develops below $T_{\textrm{N}} = 6\sim6.6$ K. The critical exponent of the magnetic order parameter was determined to be $\beta = 0.11(1)$, which is close to the two-dimensional Ising model. Additionally, the angular dependence of the magnetic critical field of the zigzag antiferromagnetic order for the polarized ferromagnetic phase reveals a six-fold rotational symmetry within the ab–plane. These findings reflect the symmetry associated with the Ising-like bond-dependent Kitaev spin interactions and underscore the universality of the Kitaev interaction-dominated antiferromagnetic system.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗

DOE OSTI2018

Structure and Magnetic Properties of Graded (001)-Oriented FePt Films Prepared by Magnetron Sputtering and Rapid Thermal Annealing

L1{sub 0}-FePt/[Fe/Pt]{sub 27} multilayer films were prepared on (100)-oriented single-crystal MgO substrates. Structural analysis indicates epitaxial growth of the L1{sub 0}-FePt films during high-temperature deposition. The room-temperature-deposited [Fe/Pt]{sub 27} multilayer exhibits the fcc-FePt structure grown epitaxially on the L1{sub 0}-FePt base layer. The degree of chemical order and thereby the anisotropy of the top layer has been controlled by varying the temperature of a post-deposition annealing process. Compared with the as-deposited films, coercivities of the films annealed below 400 {sup ∘}C are substantially decreased by introducing the formation of a graded anisotropy in the partially ordered top layer. Coercivities decrease for annealing temperatures that are greater than 400 {sup ∘}C due to improved ordering of the top layer.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗

DOE OSTI2018

Simple Hydrothermal Synthesis for Mesoporous Pebble-Like NiCo{sub 2}O{sub 4} Nanostructures and Their Attractive Magnetic Properties

The mesoporous pebble-like NiCo{sub 2}O{sub 4} nanostructures were smoothly obtained via a simple hydrothermal route and the succeeding annealing treatment. Various techniques, including XRD, SEM, TEM, Raman spectra, FTIR, and MH curves have been used to study the obtained products. The obtained results exhibited that the morphology of spinel NiCo{sub 2}O{sub 4} could be controlled by adjusting the content of cetyltrimethylammonium bromide (CTAB). The morphology of NiCo{sub 2}O{sub 4} nanostructures transformed from a 300-nm popcorn-like to 30–40-nm pebble-like nanostructure by changing the content of CTAB. Compared with the popcorn-like NiCo{sub 2}O{sub 4} nanostructures, the pebble-like samples showed effective blue shifting of Raman spectroscopy, which might be due to the nano-sized effect of NiCo{sub 2}O{sub 4} particles. Finally, vibration sample magnetometer (VSM) measurements indicated the samples transformed from weak ferromagnetic (popcorn-like) to paramagnetic (pebble-like) due to small particle size.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗

DOE OSTI2018

Effect of Laser Fluence on Magnetic Properties of Thin Mn{sub x}Si{sub 1 –} {sub x} (x ≈ 0.5) Films Prepared by Pulsed Laser Deposition

Abstract—The effect of laser pulse energy E on the possibility of forming of a homogeneous “high-temperature” ferromagnetic phase in Mn{sub x}Si{sub 1 –} {sub x} (x ≈ 0.5) alloy films grown by pulsed laser deposition onto an Al{sub 2}O{sub 3} (0001) substrate has been studied. The high-temperature phase with manganese concentration x ≈ 0.53 and the Curie temperature T{sub C} ~ 200–300 K is shown to form near the substrate at the initial stage of the film growth. In this case, high values E ≥ 6.8 J/cm{sup 2} favor the stabilization of this phase over all film thickness, while low values E = 2.6–5.7 J/cm{sup 2} lead to a decrease in the manganese concentration in the upper film layer and the formation of additional “low–temperature” phase with T{sub C} ≈ 30–50 K provided by silicides MnSi and Mn{sub 4}Si{sub 7} crystallites.

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

The Effect of the Composition of a Carrier Gas during the Growth of a Mn delta-Layer on the Electrical and Magnetic Properties of GaAs Structures

The effect of the arsine content (from 0 to 8 μmol), supplied to a reactor together with hydrogen, on the formation of delta-doped gallium-arsenide structures by the pulsed laser sputtering of a Mn target is investigated. It is found that an arsine molar fraction of ~2.5 μmol in the reactor atmosphere during the formation of a Mn delta-doped GaAs layer allows one to obtain single-crystal epitaxial structures with the lowest layer resistance and a ferromagnetic-paramagnetic phase transition temperature of about 40 K. Increasing the arsine content to 8 μmol or the absence of arsine in a hydrogen flow leads to a significant increase in the layer resistance in the temperature range below 150 K and a decrease in the Curie temperature. In the first case, this may be due to partial compensation of the hole conductivity by donor-type defects formed as a result of an excess of arsenic on the growing surface (arsenic atoms in Ga positions or in interstitial positions). In the second case, when no arsine is supplied to the reactor, the growth surface is likely to be enriched with gallium atoms, which makes the incorporation of Mn into the Ga sublattice difficult.

36 MATERIALS SCIENCE↗

DOE OSTI2018

Structural, Optical, and Magnetic Properties of Nd-Doped CeO{sub 2} Nanoparticles Codoped with Transition Metal Elements (Cu, Zn, Cr)

In the present work, pure CeO{sub 2}, neodymium-doped CeO{sub 2}, and neodymium and transition metal element (Cu, Zn, Cr)-codoped CeO{sub 2} nanoparticles were synthesized by an auto-combustion method and annealed at 700 {sup ∘}C. The X-ray diffraction (XRD) studies revealed that all the samples exhibited a single-phase cubic fluorite structure with the incorporation of respective dopant ions into the CeO{sub 2} lattice. The scanning electron microscopy (SEM) images displayed the prepared nanoparticles which had an irregular flaky structure with large agglomerations. The Fourier transform Raman (FT-Raman) spectroscopy analysis revealed the increased oxygen vacancy defects in CeO{sub 2} host after doping and codoping with neodymium and transition metal elements. Ultraviolet-diffuse reflectance spectroscopy (UV-DRS) studies revealed the decrease in bandgap values in doped and codoped samples compared to pure CeO{sub 2} sample. The Fourier transform infrared spectroscopy (FTIR) studies revealed the presence of functional groups in the prepared samples. Photoluminescence (PL) spectroscopy analysis reported the decreased luminescence intensities of Nd-doped and neodymium and transition metal-codoped CeO{sub 2} nanoparticles. The vibrating sample magnetometer (VSM) results depicted that all the samples exhibited room-temperature ferromagnetism.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗