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DOE OSTI2024

Coexistence of low and high spin states in La 18 Co 28 Pb 3

The electronic structure and magnetic properties of a newly predicted stable ternary compound La 18 ⁢Co 28 ⁢Pb 3 are studied using electronic structure analysis. The ground state of this compound is ferromagnetic, with three positions of nonequivalent magnetic Co atoms. A strong dependence of magnetic properties on volume shows that this system is situated near the point of magnetic instability. The coexistence of high- and low-spin ferromagnetic states as a function of volume near equilibrium was discovered. A corresponding spin tunneling splitting was estimated. The stability of the theoretically predicted magnetic ground state was tested by varying the Hubbard parameter. The thermal spin fluctuations were added to estimate the paramagnetic moment and a Curie temperature. Finally, the necessity of experimental verification of the obtained results is emphasized.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗

DOE OSTI2019

Properties of MgFe{sub 2}O{sub 4} Nanoparticles Synthesized by Ultrasonic Aerosol Pyrolysis for Biomedical Applications

We present the data of studies on the structure, phase states, and magnetic properties of magnetic nanoparticles (MNPs) of magnesium ferrite spinel (MgFe{sub 2}O{sub 4}), synthesized by ultrasonic aerosols pyrolysis. Primary single-phase MNPs with an average size of 9.6, 11.5, and 14.0 nm, synthesized from precursors at concentrations of 0.06, 0.12, and 0.24 M, respectively, agglomerate into tightly aggregated spherical particles (secondary particles) with sizes of 206, 300, and 340 nm, respectively. Primary particles inside the spheres do not interact with each other and are in a superparamagnetic state. There is a layer on the surface of the particles, the magnetic structure of which differs from the structure of the inner part of the MNP; this is explained by the formation of a canted spin structure or a spin glass state in the surface layer of the MNPs. MgFe{sub 2}O{sub 4} nanospheres obtained from a precursor at a concentration of 0.06 M are most promising as valid sources of heat in magnetic hyperthermia therapy.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗

DOE OSTI2014

Magnetic and magnetocaloric properties of Ba and Ti co-doped SrRuO{sub 3}

Temperature evolution of magnetic properties in Ba and Ti doped SrRuO{sub 3} has been investigated to observe the effects of larger ionic radius Ba at Sr site and isovalent nonmagnetic impurity Ti at Ru site. Ionic radius mismatch and different electronic configuration in comparison with Ru modify Sr(Ba)-O and Ru(Ti)-O bond lengths and Ru-O-Ru bond angle. The apical and basal Ru-O-Ru bond angles vary significantly with Ti doping. Ferromagnetic Curie temperature decreases from 161 K to 149 K monotonically with Ba (10%) and Ti (10%) substitutions at Sr and Ru sites. The zero field cooled (ZFC) magnetization reveals a prominent peak which shifts towards lower temperature with application of magnetic field. The substitution of tetravalent Ti with localized 3d{sup 0} orbitals for Ru with more delocalized 4d{sup 4} orbitals leads to a broad peak in ZFC magnetization. A spontaneous ZFC magnetization becomes negative below 160 K for all the compositions. The occurrence of both normal and inverse magnetocaloric effects in Ba and Ti co-doped SrRuO{sub 3} makes the system more interesting.

71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSIC↗

DOE OSTI2018

Tunable Spectral Ordering of Magnetic Plasmon Resonances in Noble Metal Nanoclusters

Experimental characterization of the optical and magnetic properties of noble metal nanoclusters has exposed a size regime in between single-ring and extended two-dimensional nanocluster networks where the behavior of magnetic plasmon resonances is not well understood. In this intermediate size regime, individual electric dipole plasmons on each nanoparticle within the cluster can hybridize into delocalized magnetic modes that couple to either the electric or magnetic field of light with seemingly arbitrary energy ordering. In this work, using a coupled-dipole model that includes fully retarded interactions between electric dipole plasmons, we show that magnetic plasmon resonance energies can be controllably tuned and even made to cross as a function of nanocluster size. Experimental confirmation of this prediction is challenging because optical selection rules dictate the simultaneous excitation of many spectrally overlapping magnetic plasmon modes. However, based on analytic modeling and numerical simulation, we show that angle-resolved cathodoluminescence offers an approach to cleanly isolate these magnetic modes and observe the size-dependence of their spectrum. Not only does our work clarify the rich optical and magnetic behavior of noble metal nanoclusters in the intermediate-size regime, but it also suggests strategies to design negative-index plasmonic metamaterials with multiple tunable resonances in the visible spectrum.

36 MATERIALS SCIENCE↗

DOE OSTI2014

Electromagnetic momentum and the energy–momentum tensor in a linear medium with magnetic and dielectric properties

In a continuum setting, the energy–momentum tensor embodies the relations between conservation of energy, conservation of linear momentum, and conservation of angular momentum. The well-defined total energy and the well-defined total momentum in a thermodynamically closed system with complete equations of motion are used to construct the total energy–momentum tensor for a stationary simple linear material with both magnetic and dielectric properties illuminated by a quasimonochromatic pulse of light through a gradient-index antireflection coating. The perplexing issues surrounding the Abraham and Minkowski momentums are bypassed by working entirely with conservation principles, the total energy, and the total momentum. We derive electromagnetic continuity equations and equations of motion for the macroscopic fields based on the material four-divergence of the traceless, symmetric total energy–momentum tensor. We identify contradictions between the macroscopic Maxwell equations and the continuum form of the conservation principles. We resolve the contradictions, which are the actual fundamental issues underlying the Abraham–Minkowski controversy, by constructing a unified version of continuum electrodynamics that is based on establishing consistency between the three-dimensional Maxwell equations for macroscopic fields, the electromagnetic continuity equations, the four-divergence of the total energy–momentum tensor, and a four-dimensional tensor formulation of electrodynamics for macroscopic fields in a simple linear medium.

71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSIC↗

DOE OSTI2022

Revealing room temperature ferromagnetism in exfoliated Fe 5 GeTe 2 flakes with quantum magnetic imaging

Van der Waals (vdW) material Fe 5 GeTe 2 , with its long-range ferromagnetic ordering near room temperature, has significant potential to become an enabling platform for implementing novel spintronic and quantum devices. To pave the way for applications, it is crucial to determine the magnetic properties when the thickness of Fe 5 GeTe 2 reaches the few-layers regime. However, this is highly challenging due to the need for a characterization technique that is local, highly sensitive, artifact-free, and operational with minimal fabrication. Prior studies have indicated that Curie temperature T C can reach up to close to room temperature for exfoliated Fe 5 GeTe 2 flakes, as measured via electrical transport; there is a need to validate these results with a measurement that reveals magnetism more directly. Here, we investigate the magnetic properties of exfoliated thin flakes of vdW magnet Fe 5 GeTe 2 via quantum magnetic imaging technique based on nitrogen vacancy centers in diamond. Through imaging the stray fields, we confirm room-temperature magnetic order in Fe 5 GeTe 2 thin flakes with thickness down to 7 units cell. The stray field patterns and their response to magnetizing fields with different polarities is consistent with previously reported perpendicular easy-axis anisotropy. Furthermore, we perform imaging at different temperatures and determine the Curie temperature of the flakes at ≈300 K. These results provide the basis for realizing a room-temperature monolayer ferromagnet with Fe 5 GeTe 2 . This work also demonstrates that the imaging technique enables rapid screening of multiple flakes simultaneously as well as time-resolved imaging for monitoring time-dependent magnetic behaviors, thereby paving the way towards high throughput characterization of potential two-dimensional (2D) magnets near room temperature and providing critical insights into the evolution of domain behaviors in 2D magnets due to degradation.

2D magnet↗

DOE OSTI2025

Current Advances in i‐MAX Phases and their Two Dimensional Derivative i‐MXenes: Challenges and Opportunities (Adv. Electron. Mater. 21/2025)

The discovery of quaternary (M′ 2/3 M′′ 1/3 ) 2 AX phases has introduced newly ordered i-MAX phases in the MAX phase community. These atomically layered solids display in-plane chemical ordering of M′ and M′′, featuring a frustrated triangular lattice overlaid on an M′ honeycomb arrangement and an A Kagomé lattice. This unique structure gives rise to novel electronic and magnetic properties, paving the way for diverse applications and the creation of new MXenes. Both experimental and theoretical research have confirmed that these i-MAX phases can be chemically exfoliated into single- or multilayered and vacancy-ordered 2D transition metal carbides, known as i-MXenes. These 2D i-MXenes exhibit intriguing optical, electrochemical, piezoelectric, and magnetic properties, which are decidedly reliant on the surface functional groups (-F, -OH, -O). This review encompasses all available theoretical and experimental studies on i-MAX and i-MXenes, with a focus on their fundamental properties, organized in multiple sections. Along with the experimental investigation, significant attention is also directed toward theoretical predictions of potential i-MAX phases and i-MXenes, including their structural, vibrational, electronic, optical, magnetic, mechanical, piezoelectric, and electrochemical properties. This article provides a comprehensive understanding of vital properties of these materials by providing a review of foundational literature with existing challenges, limitations, and future perspectives.

electrochemical, electronic↗

DOE OSTI2019

Oxygen Vacancy-Induced Room Temperature Ferromagnetism in Rutile TiO{sub 2}

As oxygen vacancies play an important role in ferromagnetism of rutile TiO{sub 2}, a method of γ-ray irradiates rutile TiO{sub 2} single crystals was subtly proposed to study the effect of oxygen vacancies on magnetic properties. Remarkably, room temperature ferromagnetism was observed in γ-ray irradiated rutile TiO{sub 2} single crystals, and the saturation magnetization is the strongest when dose is 4 × 10{sup 4} Gy which assigned to ESR results. Since the displacement threshold energy of Ti atom is much bigger than that of O atom, the defects produced by γ-irradiation are mainly oxygen vacancies. After irradiation, XPS, PL spectra indicate the presence of oxygen vacancies(V{sub O}), Ti{sup 3+}, and V{sub O}-Ti{sup 3+} composite defects.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗

DOE OSTI2014

The interplay of microstructure and magnetism in La{sub 3}Ni{sub 2}SbO{sub 9}

La{sub 3}Ni{sub 2}SbO{sub 9} adopts a perovskite-related structure in which the six-coordinate cation sites are occupied alternately by Ni{sup 2+} and a disordered arrangement of Ni{sup 2+}/Sb{sup 5+}. A polycrystalline sample has been studied by neutron diffraction in applied magnetic fields of 0≤H/kOe≤50 at 5 K. In 0 kOe, weak magnetic Bragg scattering consistent with the adoption of a G-type ferrimagnetic structure is observed; the ordered component of the magnetic moment was found to be 0.89(7) µ{sub B} per Ni{sup 2+} cation. This increased to 1.60(3) µ{sub B} in a field of 50 kOe. Transmission electron microscopy revealed variations in the Ni:Sb ratio across crystallites of the sample. It is proposed that these composition variations disrupt the magnetic superexchange interactions within the compound, leading to domain formation and a reduced average moment. The application of a magnetic field aligns the magnetisation vectors across the crystal and the average moment measured by neutron diffraction increases accordingly. The role played by variations in the local chemical composition in determining the magnetic properties invites comparison with the behaviour of relaxor ferroelectrics. - Graphical abstract: Composition variations across a crystal of La3Ni2SbO9 result in anomalous magnetic behavior. - Highlights: • Ordered magnetic moment of Ni{sup 2+} increases in an applied magnetic field. • Composition variations detected by electron microscopy. • Increase in magnetic moment can be explained by presence of composition variations.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗

DOE OSTI2017

Testing the stability of magnetic iron oxides/kaolinite nanocomposite under various pH conditions

Magnetically modified clays containing iron oxides nanoparticles (Fe{sub x}O{sub y} NPs) are low-cost and environmentally harmless materials suitable for sorption of pollutants from wastewaters. Stability of this smart material was evaluated both experimentally and theoretically using molecular modelling. Original kaolinite and prepared Fe{sub x}O{sub y}/kaolinite nanocomposite were characterized using X-ray fluorescence spectroscopy, X-ray powder diffraction, infrared spectroscopy, and transmission electron microscopy, and the stability was studied using leaching tests performed according to the European technical standard EN 12457-2 in deionized water and extraction agents with varying pH (2, 4, 9, and 11). The influence of pH on amount of Fe{sub x}O{sub y} NPs released from the composite and amount of the basic elements released from the kaolinite structure was studied using inductively coupled plasma atomic emission spectroscopy. All experiments proved that the magnetic properties of the nanocomposite will not change even after leaching in extraction agents with various pH. - Graphical abstract: The stability of magnetic Fe{sub x}O{sub y}/kaolinite nanocomposite was studied using molecular modelling and leaching tests under various pH conditions. Display Omitted - Highlights: • Magnetization by Fe{sub x}O{sub y} nanoparticles did not influenced the structure of the kaolinite. • Maghemite (γ-Fe{sub 2}O{sub 3}) and mainly magnetite (Fe{sub 3}O{sub 4}) phases were detected. • Leaching test confirmed good adhesion of Fe{sub x}O{sub y} nanoparticles on kaolinite. • Molecular modelling of kaolinite/Fe{sub x}O{sub y} nanocomposite agrees well with experiments. • Nanocomposite can be considered stable in the wide range of pH.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗

DOE OSTI2015

Structural, morphological and magnetic study of (Bi{sub 0.1}Fe{sub 0.1}O{sub 3}) - (Ni{sub 0.1}Fe{sub 2(0.1)}O{sub 4}) nanocomposite

Multiferroic nanocomposite of (Bi{sub 0.1}Fe{sub 0.1}O{sub 3}) - (Ni{sub 0.1}Fe{sub 2(0.1)}O{sub 4}) was prepared by sol gel technique and characterized by X-ray diffraction, transmission electron microscopy, superconducting quantum interference device. X-ray diffraction confirmed the formation of desired crystallographic phase of the composite. The average particle size found to be 13.97nm. The transmission electron microscopy depicts the presence of the polycrystalline nanoparticles. In order to investigate the magnetic behavior superconducting quantum interference device was used. The sample was analyzed by increasing the magnetic field up to 25kOe and magnetization was found to be 16.8emu/g, which is optimum for the technological applications. The magnetic properties in such composite result as determined both by the ferrite concentration and properties and by the degree of connectivity of the two phases. The appropriate combination of two phases gives rise to higher magnetization.

77 NANOSCIENCE AND NANOTECHNOLOGY↗

DOE OSTI2016

Evolution of the interfacial magnetic anisotropy in MgO/CoFeB/Ta/Ru based multilayers as a function of annealing temperature

We report the effect of annealing temperature on the dynamic and static magnetic properties of MgO/CoFeB/Ta/Ru multilayers. Angular resolved ferromagnetic resonance measurement results show that the as-deposited film exhibits in-plane magnetic anisotropy, whereas in the annealed films the magnetic easy-axis is almost along the direction perpendicular to the plane of the layers. The extracted interfacial anisotropy energy, K{sub i}, is maximized at an annealing temperature 225{sup ∘}C, in agreement with the vibrating sample magnetometry results. Although the magnetization is not fully out-of-plane, controlling the degree of the magnetization obliqueness may be advantageous for specific applications such as spin-transfer oscillators.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗

DOE OSTI2022

Local imaging of diamagnetism in proximity-coupled niobium nanoisland arrays on gold thin films.

In this work, we study the effect of engineered disorder on the local magnetic response of proximity-coupled superconducting island arrays by comparing scanning superconducting quantum interference device (SQUID) susceptibility measurements to a model in which we treat the system as a network of one-dimensional (1D) superconductor-normal-metal-superconductor Josephson junctions, each with a Josephson coupling energy E-J determined by the junction length or distance between islands. We find that the disordered arrays exhibit a spatially inhomogeneous diamagnetic response which, for low local applied magnetic fields, is well described by this junction network model, and we discuss these results as they relate to inhomogeneous 2D superconductors. Our model of the static magnetic response of the arrays does not fully capture the onset of nonlinearity and dissipation with increasing applied field, as these effects are associated with vortex motion due to the dynamic nature of the scanning SQUID susceptometry measurement. This work demonstrates a model 2D superconducting system with engineered disorder, and it highlights the impact of dissipation on the local magnetic properties of 2D superconductors and Josephson junction arrays.

Bishop-Van Horn, Logan↗

DOE OSTI2014

Effect of niobium addition on the martensitic transformation and magnetocaloric effect in low hysteresis NiCoMnSn magnetic shape memory alloys

The effect of Nb substitution for Ni in Ni{sub 45}Co{sub 5}Mn{sub 40}Sn{sub 10} magnetic shape memory alloys on their magnetic properties, martensitic transformation characteristics, transformation hysteresis, and magnetocaloric properties was studied using wavelength-dispersive X-ray spectroscopy, differential scanning calorimetry, and the temperature and field dependence of the magnetization. Ni{sub 45}Co{sub 5}Mn{sub 40}Sn{sub 10} alloy has a very low transformation hysteresis; however, the martensitic transformation temperatures are notably above room temperature, which is not desirable for magnetic refrigeration applications. In this study, small quantities of Nb substitution were shown to drastically shift the transformation temperatures to lower temperatures, at a rate of 68 K/at. % Nb, which is needed for household refrigeration. The austenite Curie temperature also decreased with increasing Nb content. However, a decrease in the latent heat of the martensitic transition was observed, which negatively affects the magnetic field-induced adiabatic temperature change capability. Still, the relatively large transformation entropy and the low transformation hysteresis make the Nb-doped Ni{sub 45}Co{sub 5}Mn{sub 40}Sn{sub 10} alloys potential candidates for solid state refrigeration near room temperature.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗

DOE OSTI2020

Solid state grain alignment of permanent magnets in near-final shape

Magnet microstructure manipulation in the solid state by controlled application of a sufficient stress in a direction during high temperature annealing in a single-phase region of heat-treatable magnet alloys, e.g., alnico-type magnets is followed by magnetic annealing and draw annealing to improve coercivity and saturation magnetization properties. The solid-state process can be termed highly controlled abnormal grain growth (hereafter AGG) and will make aligned sintered anisotropic magnets that meet or exceed the magnetic properties of cast versions of the same alloy types.

Anderson, Iver E.↗

DOE OSTI2022

Solid state grain alignment of permanent magnets in near-final shape

Anderson, Iver E.↗

DOE OSTI2017

Magnetic and thermal transport properties of SrFe12O19 permanent magnets with anisotropic grain structure

Not Available

Volodchenkov, A. D.↗

DOE OSTI2017

Structural and magnetic characterization of three tetranuclear Cu(II) complexes with face-sharing-dicubane/double-open-cubane like core framework

Three novel tetranuclear copper(II) complexes namely [Cu{sub 4}(L{sup 1}){sub 4}]∙2(dmf) (1), [Cu{sub 4}(L{sup 1}){sub 4}] (2) and [Cu{sub 4}(L{sup 2}){sub 2}(HL{sup 2}){sub 2}(H{sub 2}O){sub 2}]∙2(ClO{sub 4})·6(H{sub 2}O) (3) (H{sub 2}L{sup 1}, (E)−2-((1-hydroxybutan-2-ylimino)methyl)phenol; H{sub 2}L{sup 2}, (E)−2-((1-hydroxybutan-2-ylimino)methyl)−6-methoxyphenol)) were synthesized from the self-assembly of copper(II) perchlorate and the tridentate Schiff base ligands. The structural determination reveals that crystallizes in the monoclinic system with space group C2/c, whereas both the and crystallize in the triclinic system with space group P-1. and possess face-sharing dicubane core, on the other hand complex 3 has double open cubane core structure. The copper(II) ions in the cubane core are in distorted square planar geometries, and weak π…π and C–H…π interactions lead to formation of a 2D supramolecular architecture for and . At room temperature and , exhibit fluorescence with a quantum yield (Φ{sub s}) of 0.47, 0.49 and 0.38, respectively. Variable temperature magnetic susceptibility measurements in the range 2–300 K indicate an overall weak antiferromagnetic exchange coupling in all complexes. The PHI program was used to study their magnetic behaviour. In agreement with their face-sharing dicubane structure, a Hamiltonian of the type H =– J{sub 1}(S{sub 1}S{sub 2}+S{sub 1}S{sub 2’}+S{sub 1'}S{sub 2}+S{sub 1'}S{sub 2’}) – J{sub 2}S{sub 1}S{sub 1’}, where S{sub 1} = S{sub 1’} = S{sub 2} = S{sub 2’} = S{sub Cu} =1/2, was used for studying and . Simulations performed suggest magnetic exchange constants with values close to J{sub 1} =−20 cm{sup −1} and J{sub 2} =0 cm{sup -1} for these complexes. On the other hand, the spin Hamiltonian H =– J{sub 1}(S{sub 1}S{sub 4}+S{sub 2}S{sub 3}) – J{sub 2}(S{sub 1}S{sub 3}+S{sub 2}S{sub 4}) – J{sub 3}S{sub 1}S{sub 2}, where S{sub 1} = S{sub 2} = S{sub 3} = S{sub 4} = S{sub Cu} =1/2, was used to study the magnetic behaviour of the double open cubane core of and a good agreement between the experimental and simulated results was found by using the parameters g{sub 1} = g{sub 2} =2.20, g{sub 3} = g{sub 4} =2.18, J{sub 1} =−36 cm{sup -1}, J{sub 2} =−44 cm{sup -1} and J{sub 3} =0 cm{sup -1}. - Graphical abstract: Tetranuclear Cu(II) complexes with face-sharing-dicubane / double-open-cubane like core frameworks were synthesized and characterized by crystal structure and magnetic analysis. Variable temperature magnetic properties corroborate with their structural arrangement. - Highlights: • Novel tetranuclear copper(II) complexes have been structurally characterized. • Complexes possess face-sharing dicubane/double open cubane core structures. • Variable temperature magnetic measurements reveal antiferromagnetic coupling. • PHI program was used to explain the observed magnetic properties.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗