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All sourcesNASA NTRSDOE OSTI
DOE OSTI2016

Magnetic and magneto-transport studies of substrate effect on the martensitic transformation in a NiMnIn shape memory alloy

The effect of substrates on the magnetic and transport properties of Ni{sub 2}Mn{sub 1.5}In{sub 0.5} ultra-thin films were studied theoretically and experimentally. High quality 8-nm films were grown by laser-assisted molecular beam epitaxy deposition. Magneto-transport measurements revealed that the films undergo electronic structure transformation similar to those of bulk materials at the martensitic transformation. The temperature of the transformation depends strongly on lattice parameters of the substrate. To explain this behavior, we performed DFT calculations on the system and found that different substrates change the relative stability of the ferromagnetic (FM) austenite and ferrimagnetic (FiM) martensite states. We conclude that the energy difference between the FM austenite and FiM martensite states in Ni{sub 2}Mn{sub 1.5}In{sub 0.5} films grown on MgO (001) substrates is ΔE = 0.20 eV per NiMnIn f.u, somewhat lower compared to ΔE = 0.24 eV in the bulk material with the same lattice parameters. When the lattice parameters of Ni{sub 2}Mn{sub 1.5}In{sub 0.5} film have values close to those of the MgO substrate, the energy difference becomes ΔE = 0.08 eV per NiMnIn f.u. These results suggest the possibility to control the martensitic transition in thin films through substrate engineering.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2018

Influence of Chromium Doping on Electrical and Magnetic Behavior of Nd{sub 0.5}Sr{sub 0.5}MnO{sub 3} System

With a view to understand the influence of chromium doping at the Mn site on the electrical and magnetic behavior of the Nd{sub 0.5}Sr{sub 0.5}MnO{sub 3} manganite system, a series of samples were prepared by the citrate sol–gel route method. The samples were characterized structurally by XRD. A systematic investigation of electrical resistivity over a temperature range 5–300 K was carried out mainly to understand the magneto-transport behavior in these materials. Studies on the variation of magnetization with temperature over a temperature range 80–330 K were undertaken. Investigation of magnetization at different magnetic fields at two different temperatures, viz. 80 and 300 K, was also carried out. The results show that chromium doping gave typical electrical and magnetic properties. It has been concluded that the coexistence of charge ordered and ferromagnetic phases induced by chromium doping plays an important role in the low-temperature behavior of the system.

36 MATERIALS SCIENCE↗
DOE OSTI2022

Interwoven atypical quantum states in CeLiBi 2

Here we report the discovery of CeLiBi 2 , the first example of a material in the tetragonal CeTX 2 ( T = transition metal; X = pnictogen) family wherein an alkali cation replaces the typical transition metal. Magnetic susceptibility and neutron powder diffraction measurements are consistent with a crystal-field Γ 6 ground-state Kramers doublet that orders antiferromagnetically below T N = 3.4 K with an incommensurate propagation wave vector k = ( 0, 0.0724(4), 0.5) that generates a nanometric modulation of the magnetic structure. The best model of the ordered state is an elliptical cycloid with Ce moments primarily residing in the ab plane. This is highly unusual, as all other Γ 6 CeTX 2 members order ferromagnetically. Further, we observe an atypical hard-axis metamagnetic transition at 2 T in magnetostriction, magnetization, and resistivity measurements. CeLiBi 2 is a rare example of a highly conductive material with dominant skew scattering leading to a large anomalous Hall effect. Quantum oscillations with five frequencies arise in magnetostriction and magnetic susceptibility data to T = 30 K and μ 0 H = 55 T, which indicate small Fermi pockets of light carriers with effective masses as low as 0.07 m e . Density functional theory calculations indicate that square-net Dirac-like Bi-p bands are responsible for these ultralight carriers. Together, our results show that CeLiBi 2 enables multiple atypical magnetic and electronic properties in a single clean material.

36 MATERIALS SCIENCE↗
DOE OSTI2015

Temperature-dependent polymorphism and magnetic properties of three-dimensional copper pyromellitate coordination polymers containing 4,4′-dipyridylamine

A pair of three-dimensional divalent copper pyromellitate (1,2,4,5-benzene-tetracarboxylate, pyro) coordination polymers containing 4,4′-dipyridylamine (dpa) was hydrothermally prepared and structurally characterized by single-crystal X-ray diffraction. The higher-temperature phase ([H{sub 2}dpa][Cu{sub 3}(pyro){sub 2}(H{sub 2}O){sub 3}]·2.5H{sub 2}O){sub n} (1) displays an acentric 3-D 4,4,6-connected anionic network with (4{sup 4}5.6)(5{sup 4}8{sup 2})(4{sup 4}5{sup 4}6{sup 3}7{sup 4}) topology, featuring (Cu{sub 2}(OCO){sub 4}) paddlewheel dimers and isolated copper ions. Charge-balancing H{sub 2}dpa cations are embedded in incipient voids. Prepared at lower temperature, ([Cu{sub 3}(pyro){sub 2}(dpa){sub 2}(dpaH){sub 2}]·3H{sub 2}O){sub n} (2) manifests a 3-D 4,4,4-connected neutral network with uncommon (4{sup 2}6{sup 4}){sub 4}(6{sup 4}8{sup 2}) frl topology based on (Cu{sub 3}(OCO){sub 2}) linear trimers. Antiferromagnetic coupling (J=–82(5) cm{sup –1}) was observed within the (Cu{sub 2}(OCO){sub 4}) dimeric units in 1, while weak ferromagnetic coupling (J=1.0(4) cm{sup –1}) was evident for the (Cu{sub 3}(OCO){sub 2}) linear trimers in 2. Thermal degradation behavior of these new materials is also presented. - Graphical abstract: Two copper pyromellitate coordination polymers containing 4,4′-dipyridylamine were prepared. The higher-temperature phase ([H{sub 2}dpa][Cu{sub 3}(pyro){sub 2}(H{sub 2}O){sub 3}]∙2.5H{sub 2}O){sub n} displays an acentric 3-D trinodal anionic network with (4{sup 4}5.6)(5{sup 4}8{sup 2})(4{sup 4}5{sup 4}6{sup 3}7{sup 4}) topology, featuring antiferromagnetically coupled (Cu{sub 2}(OCO){sub 4}) paddlewheel dimers and isolated copper ions. - Highlights: • Copper pyromellitate (pyro) coordination polymers with 4,4′-dipyridylamine (dpa). • Higher-temperature phase 1 has 3-D anionic trinodal network with H{sub 2}dpa cations. • Lower-temperature phase 2 has rare 3-D frl network. • Dimers and chains in 1 show antiferromagnetism, trimers in 2 show ferromagnetism.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2014

Interplay between strain, quantum confinement, and ferromagnetism in strained ferromagnetic semiconductor (In,Fe)As thin films

We systematically investigated the influence of strain on the electronic structure and ferromagnetism of (In,Fe)As thin films. It is found that while the shift of the critical point energies of compressive-strained (In,Fe)As layers grown on (In{sub 1−y},Ga{sub y})As (y = 0.05, 0.1) buffer layers can be explained by the hydrostatic deformation effect (HDE) alone, those of tensile-strained (In,Fe)As layers grown on (Ga{sub 1−z},Al{sub z})Sb (z = 0, 0.5, 1) buffer layers can be explained by the combination of HDE and the quantum confinement effect (QCE). The Curie temperature T{sub C} of the (In,Fe)As layers strongly depends on the strain, and shows a maximum for the (In,Fe)As layer grown on a GaSb buffer layer. The strain dependence of T{sub C} can be explained by the s-d exchange mechanism taking into account HDE and QCE.

36 MATERIALS SCIENCE↗
DOE OSTI2021

Magnetism in metastable and annealed compositionally complex alloys

Compositionally complex materials (CCMs) present a potential paradigm shift in the design of magnetic materials. These alloys exhibit long-range structural order coupled with limited or no chemical order. As a result, extreme local environments exist with a large variations in the magnetic energy terms, which can manifest large changes in the magnetic behavior. In the current work, the magnetic properties of (Cr, Mn, Fe, Ni) alloys are presented. These materials were prepared by room-temperature combinatorial sputtering, resulting in a range of compositions with a single bcc structural phase and no chemical ordering. The combinatorial growth technique allows CCMs to be prepared outside of their thermodynamically stable phase, enabling the exploration of otherwise inaccessible order. The mixed ferromagnetic and antiferromagnetic interactions in these alloys causes frustrated magnetic behavior, which results in an extremely low coercivity (<1mT), which increases rapidly at 50 K. At low temperatures, the coercivity achieves values of nearly 500 mT, which is comparable to some high-anisotropy magnetic materials. Further, commensurate with the divergent coercivity is an atypical drop in the temperature dependent magnetization. These effects are explained by a mixed magnetic phase model, consisting of ferro-, antiferro-, and frustrated magnetic regions, and are rationalized by simulations. A machine-learning algorithm is employed to visualize the parameter space and inform the development of subsequent compositions. Annealing the samples at 600 °C orders the sample, more-than doubling the Curie temperature and increasing the saturation magnetization by as much as 5×. Simultaneously, the large coercivities are suppressed, resulting in magnetic behavior that is largely temperature independent over a range of 350 K. The ability to transform from a hard magnet to a soft magnet over a narrow temperature range makes these materials promising for heat-assisted recording technologies.

36 MATERIALS SCIENCE↗
DOE OSTI2016

Insulating nanomagnets driven by spin torque

Magnetic insulators, such as yttrium iron garnet (Y 3 Fe 5 O 12 ), are ideal materials for ultra-low power spintronics applications due to their low energy dissipation and efficient spin current generation and transmission. Recently, it has been realized that spin dynamics can be driven very effectively in micrometer-sized Y 3 Fe 5 O 12 /Pt heterostructures by spin-Hall effects. We demonstrate here the excitation and detection of spin dynamics in Y 3 Fe 5 O 12 /Pt nanowires by spin-torque ferromagnetic resonance. The nanowires defined via electron-beam lithography are fabricated by conventional room temperature sputtering deposition on Gd 3 Ga 5 O 12 substrates and lift-off. We observe field-like and anti-damping-like torques acting on the magnetization precession, which are due to simultaneous excitation by Oersted fields and spin-Hall torques. The Y 3 Fe 5 O 12 /Pt nanowires are thoroughly examined over a wide frequency and power range. We observe a large change in the resonance field at high microwave powers, which is attributed to a decreasing effective magnetization due to microwave absorption. By comparing different nanowire widths, the importance of geometrical confinements for magnetization dynamics becomes evident. In conclusion, our results are the first stepping stones toward the realization of integrated magnonic logic devices based on insulators, where nanomagnets play an essential role.

36 MATERIALS SCIENCE↗
DOE OSTI2022

Computing diffraction patterns of microstructures from phase-field simulations

The diffraction pattern of a material contains information not only on the crystal structures of its constituting phases, but also on its mesoscale spatial distributions of phases, grains, and ferroelastic, ferroelectric, and ferromagnetic domains. While diffraction patterns from experiments such as X-ray diffraction are presented in the reciprocal or Fourier space, mesoscale microstructure models such as the phase-field method naturally produce real-space images of spatial distribution of chemical composition, structural, and ferroic domains. Although one could rather readily compute the Fourier amplitudes of chemical and structural domain distributions generated by mesoscale simulations, they only contain information about the length scale and alignment of the real-space chemical and structure domains. Therefore, a direct comparison between diffraction experiments and mesoscale microstructure simulations is not possible. Here, we develop a theoretical approach to directly compute the crystal diffraction patterns of microstructures predicted by phase-field simulations. In particular, we consider five representative examples of microstructure patterns involving purely compositional domains, a single pair of tetragonal twin structures, multiple twin variants in a hexagonal system, ferroelectric polar vortices, and polycrystalline grains. The results are compared with previous experimental observations as well as X-ray diffraction experiments performed in the present study. Furthermore, the theoretical framework allows one to directly connect material microstructures and diffraction patterns predicted from phase-field simulations and the corresponding diffraction patterns from experiments, and thus providing guidance to experimental diffraction characterization and interpretation of microstructures.

36 MATERIALS SCIENCE↗
DOE OSTI2014

Tuning electronic and magnetic properties of armchair|zigzag hybrid graphene nanoribbons by the choice of supercell model of grain boundaries

Grain boundaries (GBs) attract much interest for its ability to tune the property of hybrid materials. Theoretically predicting the properties of hybrid graphene with GBs, even a linear GB remains challenging due to its inhomogeneous structure, which makes supercell model tough to choose in theoretic studies. For the first time, the applicability of supercells with different GBs and lattice-mismatches for describing armchair-zigzag hybrid graphene nanoribbons was validated by ab initio molecular dynamic simulations and first principles electronic structure calculations. And to what extent the electronic properties can be tuned by the strain effects resulting from the lattice-mismatch and the GBs distortion in supercells was demonstrated. This work showed that the intrinsic strain in such system plays a decisive role in determining the band structure and spin polarization properties. Hybrid graphene nanoribbon was found to be ferromagnetic in the ground state, especially for the case of using the supercell with nearly-perfect lattice match. Its high Curie temperature suggests the potential applications of this material in spintronics.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2013

First principles study of Fe in diamond: A diamond-based half metallic dilute magnetic semiconductor

Half-metallic ferromagnetic ordering in semiconductors, essential in the emerging field of spintronics for injection and transport of highly spin polarised currents, has up to now been considered mainly in III–V and II–VI materials. However, low Curie temperatures have limited implementation in room temperature device applications. We report ab initio Density Functional Theory calculations on the properties of Fe in diamond, considering the effects of lattice site, charge state, and Fermi level position. We show that the lattice sites and induced magnetic moments of Fe in diamond depend strongly on the Fermi level position and type of diamond co-doping, with Fe being energetically most favorable at the substitutional site in p-type and intrinsic diamond, while it is most stable at a divacancy site in n-type diamond. Fe induces spin polarized bands in the band gap, with strong hybridization between Fe-3d and C-2s,2p bands. We further consider Fe-Fe spin interactions in diamond and show that substitutional Fe{sup +1} in p-type diamond exhibits a half-metallic character, with a magnetic moment of 1.0 μ{sub B} per Fe atom and a large ferromagnetic stabilization energy of 33 meV, an order of magnitude larger than in other semiconductors, with correspondingly high Curie temperatures. These results, combined with diamond's unique properties, demonstrate that Fe doped p-type diamond is likely to be a highly suitable candidate material for spintronics applications.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2016

Multi-frequency ferromagnetic resonance investigation of nickel nanocubes encapsulated in diamagnetic magnesium oxide matrix

For this, partially aligned nickel nanocubes were grown epitaxially in a diamagnetic magnesium oxide (MgO:Ni) host and studied by a continuous wave ferromagnetic resonance (FMR) spectroscopy at the X-band (9.5 GHz) from ca. 117 to 458 K and then at room temperature for multiple external magnetic fields/resonant frequencies from 9.5 to 330 GHz. In contrast to conventional magnetic susceptibility studies that provided data on the bulk magnetization, the FMR spectra revealed the presence of three different types of magnetic Ni nanocubes in the sample. Specifically, three different ferromagnetic resonances were observed in the X-band spectra: a line 1 assigned to large nickel nanocubes, a line 2 corresponding to the nanocubes exhibiting saturated magnetization even at ca. 0.3 T field, and a high field line 3 (g eff ~ 6.2) tentatively assigned to small nickel nanocubes likely having their hard magnetization axis aligned along or close to the direction of the external magnetic field. Based on the analysis of FMR data, the latter nanocubes possess an anisotropic internal magnetic field of at least ~1.0 T in magnitude.

36 MATERIALS SCIENCE↗
DOE OSTI2024

Scanning SQUID study of ferromagnetism and superconductivity in infinite-layer nickelates

Infinite-layer nickelates R 1-x Sr x NiO 2 (R = La, Pr, Nd) are a class of superconductors with structural similarities to cuprates. Although long-range antiferromagnetic order has not been observed for these materials, magnetic effects such as antiferromagnetic spin fluctuations and spin-glass behavior have been reported. Different experiments have drawn different conclusions about whether the pairing symmetry is s or d wave. In this paper, we applied a scanning superconducting quantum interference device (SQUID) to probe the magnetic behavior of film samples of three infinite-layer nickelates (La 0.85 Sr 0.15 NiO 2 , Pr 0.8 Sr 0.2 NiO 2 , and Nd 0.775 Sr 0.225 NiO 2 ) grown on SrTiO 3 (STO), each with a nominal thickness of 20 unit cells. In all three films, we observed a ferromagnetic background. We also measured the magnetic susceptibility above the superconducting critical temperature in Pr 0.8 Sr 0.2 NiO 2 and La 0.85 Sr 0.15 NiO 2 and identified a non-Curie-Weiss dynamic susceptibility. Both magnetic features are likely due to NiO x nanoparticles. We investigated superconductivity in Pr 0.8 Sr 0.2 NiO 2 and Nd 0.775 Sr 0.225 NiO 2 , which exhibited inhomogeneous diamagnetic screening. The superfluid density inferred from the diamagnetic susceptibility in relatively homogeneous regions shows T-linear behavior in both samples. Finally, we observed superconducting vortices in Nd 0.775 Sr 0.225 NiO 2 . We determined a Pearl length of 330 µm for Nd 0.775 Sr 0.225 NiO 2 at 300 mK, both from the strength of the diamagnetism and from the size and shape of the vortices. These results highlight the importance of considering NiO x particles when interpreting experimental results for these films.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2016

Synthesis, crystal structure, and magnetism of A{sub 2}Co{sub 12}As{sub 7} (A=Ca, Y, Ce–Yb)

Ternary intermetallics, A{sub 2}Co{sub 12}As{sub 7} (A=Ca, Y, Ce–Yb), have been synthesized by annealing mixtures of elements in molten Bi at 1223 K. The materials obtained crystallize in the P6{sub 3}/m variant of the Zr{sub 2}Fe{sub 12}P{sub 7} structure type. The unit cell volume shows a monotonic decrease with the increasing atomic number of the rare-earth metal, with the exception of Ce-, Eu-, and Yb-containing compounds. An examination of these outliers with X-ray absorption near edge structures (XANES) spectroscopy revealed mixed valence of Ce, Eu, and Yb, with the average oxidation states of +3.20(1), +2.47(5), and +2.91(1), respectively, at room temperature. Magnetic behavior of A{sub 2}Co{sub 12}As{sub 7} is generally characterized by ferromagnetic ordering of Co 3d moments at 100–140 K, followed by low-temperature ordering of rare-earth 4f moments. The 3d-4f magnetic coupling changes from antiferromagnetic for A=Pr–Sm to ferromagnetic for A=Ce and Eu–Yb. Polarized neutron scattering experiments were performed to support the postulated ferro- and ferrimagnetic ground states for Ce{sub 2}Co{sub 12}As{sub 7} and Nd{sub 2}Co{sub 12}As{sub 7}, respectively. - Graphical abstract: Title arsenides were synthesized by Bi‐flux method. They exhibit mixed valence for A = Ce, Eu, Yb, ferrimagnetism for A = Ca, Y, Pr–Sm, and ferromagnetism for A = Eu–Tm. - Highlights: • A2Co12As7 (A=Ca, Y, Ce–Yb) were synthesized in Bi flux. • Ce, Eu, Yb exhibit mixed valence in the corresponding structures. • The character of 3d‐4f magnetic coupling changes at the half‐filled f shell. • Materials behave as ferrimagnets for A=Ca, Y, Pr–Sm and as ferromagnets for A=Eu–Yb.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2013

Magnetic and Gilbert damping properties of L{sub 21}-Co{sub 2}FeAl film grown by molecular beam epitaxy

Co{sub 2}FeAl film with L{sub 21} structure was prepared. Its magnetic and Gilbert damping properties were studied by ferromagnetic resonance (FMR) and time-resolved magneto-optical Kerr effect (TR-MOKE), respectively. It is observed that the apparent damping parameter decreases drastically with increasing magnetic field at low field regime and eventually becomes a constant value of 0.004 at high field regime by TR-MOKE measurements. A Gilbert damping parameter of 0.008 in the hard axis by FMR measurement has also been obtained, which is comparable with that extracted from TR-MOKE measurements at low external field, indicating the extrinsic damping processes involved in the low field regime.

36 MATERIALS SCIENCE↗
DOE OSTI2022

Tuning Spin-Orbit Torques Across the Phase Transition in VO 2 /NiFe Heterostructure

The emergence of spin-orbit torques as a promising approach to energy-efficient magnetic switching has generated large interest in material systems with easily and fully tunable spin-orbit torques. We report current-induced spin-orbit torques in VO 2 /NiFe heterostructures are investigated using spin-torque ferromagnetic resonance, where the VO 2 layer undergoes a prominent insulator-metal transition. A roughly twofold increase in the Gilbert damping parameter, α, with temperature is attributed to the change in the VO 2 /NiFe interface spin absorption across the VO 2 phase transition. More remarkably, a large modulation (±100%) and a sign change of the current-induced spin-orbit torque across the VO 2 phase transition suggest two competing spin-orbit torque generating mechanisms. The bulk spin Hall effect in metallic VO 2 , corroborated by the first-principles calculation of the spin Hall conductivity σ SH ≈ -10 4 ($\frac{\hbar}{e}$) Ω -1 m -1 , is verified as the main source of the spin-orbit torque in the metallic phase. The self-induced/anomalous torque in NiFe, with opposite sign and a similar magnitude to the bulk spin Hall effect in metallic VO 2 , can be the other competing mechanism that dominates as temperature decreases. For applications, the strong tunability of the torque strength and direction opens a new route to tailor spin-orbit torques of materials that undergo phase transitions for new device functionalities.

36 MATERIALS SCIENCE↗
DOE OSTI2017

First-principles Calculations of Structural, Magnetic Electronic and Optical Properties of Rare-earth Metals TbX (X=N, O, S, Se)

The structural, magnetic, electronic and optical properties of Terbium-based binaries (TbX) (X = N, O, S and Se) in two cubic structures NaCl and CsCl have been investigated. This study is carried out by Full-Potential linearized Muffin-Tin orbitals (FP-LMTO) method in the framework of the functional theory of density (DFT) implemented in the lmtart code. The presence of f-state electrons in these induced high-correlation materials led us to study these systems using local density approximation (LDA) for the paramagnetic state and spin local density approximation (LSDA) for the ferromagnetic state within two cubic structures. We have demonstrated that these binaries are stable in the ferromagnetic state in the cubic phase of NaCl, which allows us to deduce the magnetic moments of these components. From the electronic band structures and density states, we have concluded that TbX (X = N, O, S and Se) are metallic in the NaCl phase. The results obtained in this work show that the theoretical parameters of the ground state, structure of the bands, density of the states (DOS) and optical properties agree well with other available theoretical and experimental data.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2019

Metamagnetism, Multiple Magnetic Transitions and Wide Temperature Range Magnetocaloric Effect in Dy{sub 6.5}Co{sub 2}Si{sub 2.5} Alloy

We report the structure, magnetic, thermodynamic, transport, and magnetocaloric properties of Dy{sub 6.5}Co{sub 2}Si{sub 2.5} alloy. It shows that this alloy has been formed in three phases viz., Dy{sub 5}Si{sub 3}, Dy{sub 3}Co{sub 2.2}Si{sub 1.8}, and Dy{sub 3}Co with four successive magnetic transitions named as T{sub 1}, T{sub 2}, T{sub 3},T{sub 4}, at 43, 74.7, 90.5, and 132.4 K, respectively. The magnetic measurements display competing ferromagnetic and antiferromagnetic interactions in the alloy. At 2.5 K, the alloy exhibits hard ferromagnetic properties with a coercive field of 0.8 T. Metamagnetism is also evidenced in the isothermal magnetization measurements. The Arrot plot shows that this material undergoes first-order magnetic transitions below 47 K, and above which, magnetic transitions are of second order. The four successive magnetic transitions together with competing magnetic interactions give rise to a broadened magnetocaloric effect (MCE) peak with temperature width of ΔT = 83.8 and 93.2 K and consequently a large RC value of 474 and 739 J/kg, for a magnetic field change of 0–5 and 0–7 T, respectively. Additionally, it is found that the alloy exhibits negative magnetoresistance and attains a value of − 11 and − 7% at 2.5 and 50 K, respectively, in applied magnetic field of 9 T. Thus, the peculiar magnetic and magnetocaloric properties make the Dy{sub 6.5}Co{sub 2}Si{sub 2.5} alloy promising not only for low-temperature magnetic refrigeration but also for fundamental study perspectives.

36 MATERIALS SCIENCE↗
DOE OSTI2019

Magneto-Electronic, Thermodynamic, and Thermoelectric Properties of 5f-Electron System BaBkO{sub 3}

In the present work, the structural, electronic, magnetic, mechanical, thermodynamic, and thermoelectric properties of cubic perovskite BaBkO{sub 3} were investigated within the framework of density functional theory using generalized gradient approximation, onsite Coulomb interaction, and modified Becke-Johnson methods. BaBkO{sub 3} is stable in the ferromagnetic phase with a magnetic moment of 7 μ{sub B}. The spin-polarized electronic band structure reveals 100% spin polarization of the material with metallic character in spin-up state and semiconducting in spin-down state. Pugh and Cauchy relation displays that the material is highly ductile. The quasi-harmonic Debye model was used to determine the thermodynamic properties of BaBkO{sub 3} under high pressure and temperature. BaBkO{sub 3} presents high value of Seebeck coefficient and power factor at room temperature with a value of 135 μVK{sup − 1} and 1.5 × 10{sup 12}μWcm{sup − 1} K{sup − 2} s{sup − 1}, respectively. The possession of half metallicity and high Seebeck coefficient makes BaBkO{sub 3} suitable for spintronic and thermoelectric device applications.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗