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Robust Half-Metallicity in Quaternary Heusler Compounds KSrNZ (Z = O, S, and Se)
The first principle calculations based on density functional theory using full potential linearized augmented plane wave method was performed on the quaternary Heusler alloys KSrNZ (Z = O, S, and Se). Studies on structural properties showed that quaternary Heusler alloys KSrNZ (Z = O, S, and Se) were stable in Y{sub I}-type structure. Furthermore, values of formation energies confirmed that these alloys may be synthesized experimentally. Verification of electronic properties resulted that KSrNO, KSrNS, and KSrNSe compounds were half-metals at equilibrium lattice constants with majority band gaps of 4.61, 3.82, and 3.51 eV, respectively. KSrNZ (Z = O, S, and Se) compounds maintained half-metallic behavior in relatively wide ranges of lattice constant under uniform strain distortion. This indicates that these compounds are promising materials for future spintronic applications. Furthermore, the origin of half-metallic characteristic was verified using electronic density of states. Calculations of magnetic properties showed that the total magnetic moments of KSrNZ (Z = O, S, and Se) were obtained equal to 2 μ{sub B} satisfying the famous Slater-Pauling rule (M{sub tot}= 12-Z{sub tot}).
Mixed Nd 4+/3+ and Cluster Magnetism in Hexagonal Perovskite 12R-Ba 4 NdMn 3 O 12−γ
Hexagonal perovskite oxides with 12R stacking host well-separated face-sharing octahedral metal trimers with short metal–metal distances, leading in some cases to large degrees of magnetic frustration and cluster magnetism. Introducing magnetic ions in proximity to these trimers can influence the degree of frustration and cluster magnetism, but the extent to which the magnetism can be tuned by varying neighboring metal cations remains an open question. In this work, we test the impacts of using Nd in proximity to Mn trimers in the hexagonal perovskite 12R-Ba 4 NdMn 3 O 12−γ . Given this stoichiometry, Nd should assume the 4+ oxidation state with a spin state of S = 1, which would be the first realization of Nd 4+ in an oxide environment. Through detailed bulk magnetic, X-ray absorption spectroscopic, and powder neutron diffraction (PND) measurements, we find that Nd 4+ is realized in this material, but there is also partial reduction to Nd 3+ , which is charge-balanced by O vacancies. Magnetometry measurements indicate an antiferromagnetic ordering temperature T N ≈ 16 K, and PND measurements reveal a surprising collinear antiferromagnetic structure with magnetic space group Pc2/m (no. 10.49 in BNS notation), which has not previously been seen in this class of materials. Our results represent a comprehensive analysis of the structural, electronic, and magnetic properties of 12R-Ba 4 NdMn 3 O 12−γ , showing the first observation of partial Nd 4+ in an oxide, and demonstrating that this structural class can host a broad range of magnetic structures which are not easily predicted based on compositional trends.
A Role of the 3d Electron Subsystem in the Evolution of Band Structure and Magnetic and Optical Properties of ErNi{sub 5 –} {sub x}Co{sub x} Compounds (x = 0–4)
The evolution of the electronic structure and optical and magnetic properties of ErNi{sub 5 –} {sub x}Co{sub x} compounds (x = 0–4), occurring upon substitution of nickel by cobalt atoms, has been investigated. Spin-polarization calculations of the band spectrum of these intermetallic compounds have been performed within the local spin density approximation with a correction for strong electron correlations in the 4f shell of a rare-earth ion (method LSDA+U). The values of magnetic moments for erbium, nickel, and cobalt ions (located at different crystallographic sites) are obtained. The exchange-interaction parameters for the 3d sublattice of transition metals are determined. The spectral properties of the compounds have been investigated in the wavelength range of 0.22–15 μm by optical ellipsometry. The experimental frequency dependences of the optical conductivity in the interband absorption region are compared with the corresponding characteristics calculated based on the density of electronic states.
Strong Correlation Effect in Ferrimagnetic Half-Metallic V{sub 2}CoAl and V{sub 2}CoGa Heusler Compounds
We present first-principles calculations based on the full-potential linearized augmented plane wave (FP-LAPW) method to investigate the structural, elastic, electronic, and magnetic properties of the Heusler compounds V{sub 2}CoAl and V{sub 2}CoGa. We explore different magnetic configurations in both regular and inverse Heusler structures: the Cu{sub 2}MnAl-type and Hg{sub 2}CuTi-type structures respectively. Our compounds are found to be ferrimagnets in the inverse Heusler structure. To take into account the effects of the strong correlation among the localized d-states, we perform a calculation using the GGA+U method (the general gradient approximation with the Hubbard on-site Coulomb correction U). Then we show that both compounds exhibit a half-metallic character and have a magnetic moment of 2.00 μ{sub B} per formula unit. This latter statement is coherent with the generalized Slater-Pauling rule (SP). In terms of the band structure calculations, we explain the formation of the indirect energy band gaps in the spin-majority channels. We also use the mean-field approximation (MFA) to discuss the magnetic exchange couplings and predict the Curie temperature for both compounds.
Calculations of the Structural, Elastic, Magnetic, and Electronic Properties of the New Compound BaZr{sub 0.5}Mn{sub 0.5}O{sub 3} with Tetragonal Structure
Based on the density functional theory, we have calculated the structural properties of the BaZrO{sub 3} (BZO) cubic structure with PBE-GGA, PBEsol-GGA, and LDA approximations. The equilibrium lattice constant within GGA-PBEsol (a = 4.1847 Å) is in very good agreement with the experimental data (Holland and Redfern, Miner. Mag. 61: 65, 1997). The calculations of elastic properties of pure and doped BaZrO{sub 3} are calculated with PBEsol-GGA; both BZO and BZM are compressible and show a brittle nature. According to calculated electronic and magnetic properties, it is found that Mn-doped BaZrO{sub 3} system is a half metallic and exhibits a ferromagnetic character. The total magnetic moment of the cell is equal to3.57 µ{sub B}; this value comes from manganese atom (Mn) with a value of 3.176 µ{sub B}. The magnetic moments of barium, oxygen, and zirconium atoms are approximately equal to zero.
Magnetic and Magnetodielectric Properties of Ho{sub 0.5}Nd{sub 0.5}Fe{sub 3}(BO{sub 3}){sub 4}
The magnetic and magnetodielectric properties of Ho{sub 0.5}Nd{sub 0.5}Fe{sub 3}(BO{sub 3}){sub 4} ferroborate with the competing Ho–Fe and Nd–Fe exchange couplings have been experimentally and theoretically investigated. Step anomalies in the magnetization curves at the spin-reorientation transition induced by the magnetic field B ║ c have been found. The spontaneous spin-reorientation transition temperature T{sub SR} ≈ 8 K has been refined. The measured magnetic properties and observed features are interpreted using a single theoretical approach based on the molecular field approximation and calculations within the crystal field model of the rare-earth ion. Interpretation of the experimental data includes determination of the crystal field parameters for Ho{sup 3+} and Nd{sup 3+} ions in Ho{sub 0.5}Nd{sub 0.5}Fe{sub 3}(BO{sub 3}){sub 4} and parameters of the Ho–Fe and Nd–Fe exchange couplings.
Entropy Engineering and Tunable Magnetic Order in the Spinel High-Entropy Oxide
Spinel oxides are an ideal setting to explore the interplay between configurational entropy, site selectivity, and magnetism in high-entropy oxides (HEOs). In this work, we characterize the magnetic properties of the spinel (Cr, Mn, Fe, Co, Ni) 3 O 4 and study the evolution of its magnetism as a function of nonmagnetic gallium substitution. Across the range of compositions studied here, from 0 to 40% Ga, magnetic susceptibility and powder neutron diffraction measurements show that ferrimagnetic order is robust in the spinel HEO. However, we also find that the ferrimagnetic order is highly tunable, with the ordering temperature, saturated and sublattice moments, and magnetic hardness all varying significantly as a function of Ga concentration. Through X-ray absorption and magnetic circular dichroism, we are able to correlate this magnetic tunability with strong site selectivity between the various cations and the tetrahedral and octahedral sites in the spinel structure. In particular, we find that while Ni and Cr are largely unaffected by the substitution with Ga, the occupancies of Mn, Co, and Fe are each significantly redistributed. Ga substitution also requires an overall reduction in the transition metal valence, and this is entirely accommodated by Mn. Finally, we show that while site selectivity has an overall suppressing effect on the configurational entropy, over a certain range of compositions, Ga substitution yields a striking increase in the configurational entropy and may confer additional stabilization. In conclusion, spinel oxides can be tuned seamlessly from the low-entropy to the high-entropy regime, making this an ideal platform for entropy engineering.
The Effect of Ba Doping on the Structural, Optical, Magnetic, and Dielectric Properties of BiFeO{sub 3} Nanoparticles
Nanoparticles (Nps) of Ba (0, 1 to 5 at.%)-doped BiFeO{sub 3} were synthesized by a sol-gel route at 100 °C using tartaric acid as a chelating agent. The obtained results were studied by using XRD, SEM with EDAX, TEM, UV-vis diffusion reflectance spectra, VSM, and impedance analyzer. EDAX spectra confirmed the presence of Bi, Ba, and Fe in the samples. X-ray diffraction studies showed that BiFeO{sub 3} and Bi{sub 1−x}Ba{sub x}FeO{sub 3} samples exhibited the expected rhombohedral perovskite structure up to a Ba concentration of 3%, whereas 4 and 5% of Ba concentration exhibited the tetragonal phase. TEM studies indicate the particle sizes in the range of 08–28 nm. Reflectance spectra measurements showed a decrease in band gap with increasing Ba concentration. Magnetic properties indicated that the undoped BiFeO{sub 3} and Ba-doped BiFeO{sub 3} samples were ferromagnetic at room temperature. The dielectric constant (ε{sup ′}) and loss (ε{sup ″}) show large dispersion behavior. The dielectric constant increases with an increase of dopant concentration, but a very high value of the dielectric constant was noticed for x = 0.05.
Prediction of Half-Metallic Properties in Non-transition Metal-based Binary Compounds X Bi (X = Ba, Sr and Ca) with Zinc-Blende and Wurtzite Structures
In this study, structural, electronic and magnetic properties of non-transition metal-based binary compounds X Bi (X = Ba, Sr and Ca) in five different phases: rock salt, NiAs, wurtzite, zinc blende and CsCl, are investigated in order to find new sp magnetic materials used for real spintronic and other related applications. The calculations are performed by a developed full-potential augmented plane wave plus local orbitals (FP-L/APW + lo) method within the spin density functional theory. As exchange-correlation potential, we used the generalized gradient approximation of Perdew, Burke, and Ernzerhof (GGA-PBE) and the modified Becke-Johnson potential mBJ-GGA-PBE form. It is found that the magnetic moment in these compounds is mainly contributed by the spin-polarized p orbitals of Bi atoms. The WZ XBi are true half-metallic ferromagnet with opposite spin direction at Fermi energy having a magnetic moment of 2.00 μ B per formula unit.
Tuning of the magnetotransport properties of a spin-polarized 2D electron system using visible light
We report on the effects of visible light on the low temperature electronic properties of the spin-polarized two dimensional electron system (2DES) formed at the interfaces between LaAlO 3 , EuTiO 3 and (001) SrTiO 3 . A strong, persistent modulation of both longitudinal and transverse conductivity was obtained using light emitting diodes (LEDs) with emissions at different wavelengths in the visible spectrum range. In particular, Hall effect data show that visible light induces a non-volatile electron filling of bands with mainly 3 dxz,yz character, and at the same time an enhancement of the anomalous Hall effect associated to the magnetic properties of the system. Accordingly, a suppression of the weak-anti localization corrections to the magneto-conductance is found, which correlates with an enhancement of the spin-polarization and of the ferromagnetic character of 2DES. The results establish the LED-induced photo-doping as a viable route for the control of the ground state properties of artificial spin-polarized oxide 2DES.
Electronic transport, thermal transport, thermal expansion, and magnetization in the strongly correlated metal LaNiO 3
Perovskite structured LaNiO 3 is a strongly correlated metal with intriguing thermal and magnetic properties. The volume dependence of calculated and measured physical properties can add additional critical information to develop a more in-depth understanding of this strongly correlated phenomenon. Taking advantage of recent single crystal LaNiO 3 growth using the floating-zone method, we have measured the thermal expansion, the magnetostriction, and the pressure dependence of the magnetic susceptibility, which then allows derivation of the Grüneisen parameters γ e = $\frac{dlnN(E_F)}{d lnV}$, γ χ = $\frac{dlnχ}{d lnV}$, as well as of electric and thermal transport properties. We simulate the volume dependence of structural and magnetic properties using Density Functional Theory calculations at the Generalized Gradient Approximation level. A large discrepancy between experimental values and calculated ones suggests that strong correlations are likely to be dynamic in nature. This study also provides a side-by-side comparison of measurements in single crystal and polycrystalline samples of LaNiO 3 to elucidate intrinsic materials properties. A broad hump at high temperatures in the temperature dependence of magnetization found in the single crystal sample of LaNiO 3 has been rationalized by a model that includes the influence of electron correlations on the Landau diamagnetism.
Structure-property relationship in layered BaM n 2 S b 2 and B a 2 M n 3 S b 2 O 2
Layered transition-metal compounds have received great attention owing to their physical properties. In this work, we present the structural, electronic, thermal, and magnetic properties of BaMn 2 Sb 2 and Ba 2 Mn 3 Sb 2 O 2 single crystals, both with the layered structure analogous to high-temperature Cu- and Fe-based superconductors. While the Mn moment in the MnSb 4 tetrahedral environment forms a long-range G-type antiferromagnetic (AFM) ordering in both BaMn 2 Sb 2 (T N1 ≈443K) and Ba 2 Mn 3 Sb 2 O 2 (T N1 ≈314K), a short-range AFM order is found in the intercalated MnO 2 layer at a much lower temperature (T N2 ≈60K) coexisting with long-range G-type order in MnSb 4 layer in Ba 2 Mn 3 Sb 2 O 2 . The directions of the ordered moments in these two magnetic sublattices of Ba 2 Mn 3 Sb 2 O 2 are perpendicular to each other, even though the system is electrically conductive. The G-type AFM order in MnSb 4 layers in both compounds is distinct from the stripe-like order in Fe-based superconductors, but the in-plane magnetic structure in MnO 2 layers of Ba 2 Mn 3 Sb 2 O 2 is found to be similar to that in the cuprates. Our study acknowledges the significant and distinct roles of the CuO 2 - and FeAs 4 -type transition metal layers in the structure and their magnetic and electronic properties.
Metallic materials for nonmagnetic spacecraft, properties and measurement methods
Metallic materials for nonmagnetic spacecraft - magnetic properties and measurement methods
Tailoring microstructures with mild magnetic-field processing: A case study of CuNiFe alloys
Combined experimental and computational investigations of the CuNiFe spinodal system confirm that application of a mild magnetic field during thermal treatment alters elemental redistribution and the resulting microstructure, relative to that obtained from zero-field annealing. Spinodal decomposition of a Cu 40 Ni 42 Fe 18 alloy was initiated during thermal treatment at 773 K, conducted either under zero field or modest (60 mT) magnetic f ield conditions for up to 200 h. Periodic (~10 nm) chemical modulations into Cu-rich and NiFe-rich regions were observed under both conditions, with the amplitude and wavelength of the segregated regions increasing with treatment time. However, magnetic field annealing resulted in a more than twofold increase in the amplitude of elemental modulations relative to zero-field conditions – consistent with enhanced diffusional f luxes during spinodal decomposition – while the modulation wavelength remained largely unaffected. These microstructural differences are reflected in various extrinsic magnetic properties. In parallel, first-principles DFT calculations indicate that long-range ferromagnetic order, as induced by an applied magnetic field, substantially alters the strength and nature of atomic interactions, enhancing the thermodynamic instability of the CuNiFe solid solution. Collectively, these results suggest that incorporating a mild (millitesla-level) magnetic field – distinct from the strong (tesla-level) fields commonly used in prior studies – during thermal processing has the potential to deliver enhanced control of microstructures for targeted engineering outcomes.
Spin–Flop and Metamagnetic Transition in Monoclinic Eu 4 Bi 6 Se 13
This study explores an investigation of the crystallographic, electronic, and magnetic properties of the europium-based bismuth selenide compound Eu 4 Bi 6 Se 13 , with particular focus on its magnetic anisotropy. This compound adopts a monoclinic crystal structure classified under the P2 1 /m space group (#11). It exhibits distinctive structural features, including substantial Eu–Se coordination numbers (6 and 8), Bi–Se ladders, and linear chains of Eu atoms that propagate along the b-axis. Electronic resistivity assessments indicate that Eu 4 Bi 6 Se 13 exhibits metallic behavior. As the magnetic field is oriented along the b-axis, magnetic characterization reveals uniaxial magnetic anisotropy, with metamagnetic transitions appearing at approximately 12 kOe and a lower field. In the field below 10 kOe, the spin-flop transition is observed with possible domain-induced hysteresis. This behavior supports the identification of metamagnetic features in field-dependent measurements attributable to the europium spins.
Inhomogeneous Magnetic State of Ce{sub 2}Fe{sub 17} Evidenced by Mössbauer Spectroscopy
A comparative analysis of the magnetic properties and Mössbauer spectra of two Ce{sub 2}Fe{sub 17} samples prepared by different methods and demonstrating different magnetic behavior is carried out. A model for processing the spectra is proposed, which gives a good description of the Mössbauer spectra of samples in different magnetic states by a superposition of eight subspectra. It is shown that in the samples in the ferromagnetic state there are regions with antiferromagnetic ordering at the local level. The relative fractions of iron atoms in these regions differs for different samples and increases when approaching the temperature of the transition from the ferromagnetic to the antiferromagnetic state.
The development and the results of a sputtering procedure for alfesil-yielding thin magnetic coating materials Final report
Sputtering procedure for yielding Alfesil thin magnetic coating materials - mechanical, electric, and magnetic properties of Alfesil