Crystalline Anisotropy Research Articles

Enhanced X-band absorption and shielding performance of Gd-substituted barium hexaferrite

Gd- substituted barium hexaferrite has been synthesized by solid-state ceramic method to explore its X-band (8.2 – 12.4 GHz) absorption and shielding performance. The structural, magnetic, and microwave properties of the synthesized hexaferrite were studied by X-ray diffraction (XRD), micro-Raman spectroscopy, field emission scanning electron microscopy (FESEM), vibrating sample magnetometer (VSM), and vector network analyzer (VNA). XRD patterns confirmed the hexagonal magnetoplumbite phase formation in all samples. A noticeable red shift in the Raman spectra from 710 to 705 cm-1 and 323–327 cm-1 suggested the presence of Fe2+ ions at 4f1 tetrahedral and 12k octahedral sites, respectively. Microstructural studies on as-prepared samples confirm particle size reduction up to 1.86 µm with Gd substitution. A modest increase in magnetization and remanence value for 20% Gd was noted. Coercivity increased with substitution, whereas the anisotropy field and crystalline anisotropy constant reduced with Gd addition. An overall improvement in shielding efficiency and absorption was noted for Gd- substituted samples. A maximum average shielding efficiency of 16.47 dB and effective absorption of 99.99% was recorded for 10% Gd. Overall, microwave absorbance is improved up to 97% with Gd substitution, which suggests this material can also work as an absorber in microwave device applications.

Perpendicular magnetic anisotropy induced by antiferromagnetic Mn-Pd alloy films: Dual effects of exchange and spin-orbit coupling

Ferromagnetic (FM) films with perpendicular magnetic anisotropy (PMA) are crucial building blocks of state-of-the-art perpendicular magnetic devices. This study investigated the effects of triggering PMA in FM thin films by applying ${\mathrm{Mn}}_{1\ensuremath{-}x}{\mathrm{Pd}}_{x}$-based antiferromagnetic (AFM) thin films with strong AFM exchange coupling from Mn and high spin-orbit coupling from Pd atoms. Our results reveal that ${\mathrm{Mn}}_{1\ensuremath{-}x}{\mathrm{Pd}}_{x}$ films can trigger PMA in Co/Ni films with weak in-plane magnetic anisotropy at room temperature through either ${\mathrm{Mn}}_{1\ensuremath{-}x}{\mathrm{Pd}}_{x}$-facilitated interfacial perpendicular crystalline anisotropy (spin-orbit coupling, $x \ensuremath{\ge}10%$) or incorporation of them with antiferromagnet-induced exchange coupling ($x \ensuremath{\le}10%$). In Co/Fe films with strong in-plane magnetic anisotropy, Mn-rich ${\mathrm{Mn}}_{1\ensuremath{-}x}{\mathrm{Pd}}_{x}$ films ($x \ensuremath{\le}10%$) can induce stable PMA at low temperatures through concurrently enhanced spin-orbit coupling and antiferromagnet-induced exchange coupling across the AFM--FM interface. Our research clarifies the dual effects of exchange and spin-orbit coupling in ${\mathrm{Mn}}_{1\ensuremath{-}x}{\mathrm{Pd}}_{x}$ films, which trigger the PMA of adjacent FM films. This indicates that ${\mathrm{Mn}}_{1\ensuremath{-}x}{\mathrm{Pd}}_{x}$ films are promising candidates for achieving controllable PMA.

Rare earth substituted lithium ferrite/carbon black ceramic composites for shielding electromagnetic radiation

The requirement for electromagnetic interference (EMI) shielding materials have been increased in the last few years due to the extensive usage of portable communication/wireless devices. These devices radiate harmful electromagnetic waves; hence it is imperative to explore suitable materials to protect human health from the radiation. In this study, Dy substituted lithium ferrite/carbon black (LiFe5-xDyxO8/CB) composites have been developed for better shielding efficiency. The effect of Dy on structural, microstructural, and magnetic responses is studied systematically. The fluctuations in the lattice constant are attributed to the differences in the ionic radius of Dy and Fe. The addition of Dy caused the inhibition of grain growth and the formation of irregular grains. The saturation magnetization is also enhanced with an increase in Dy concentration up to x = 0.1 (LD10FO/CB) and then decreased after that Neels’ sublattice model interprets the variation in magnetization and the effective magneto crystalline anisotropy is analyzed. The EMI shielding effectiveness (SE) due to absorption and the reflection is enhanced by incorporating Dy (in the X- and Ku- bands). A maximum SE of 26 dB is observed for x = 0.1 compositions. It is noticed that absorption is the dominant mechanism rather than reflection. The highest absorption coefficient (Aeff) of 99.6% is achieved for LD10FO/CB in the range of 17–18 GHz. The values of complex permittivity and permeability for LD10FO/CB are in the range of (20–40) and (2–6), respectively. The incorporation of Dy (rare earth ion) in spinel ferrite led to promote 4f − 3d coupling along with 3d − 3d, which helped to enhance the magnetic and electrical properties. The results demonstrate that such ceramics can be used as a commercial microwave absorber.

Phase field theory for pressure-dependent strength in brittle solids with dissipative kinetics

A phase field theory of fracture mechanics is formulated to address dependence of material strength on stress state, noting that brittle solids are usually more fracture resistant when mean stress is compressive. Fracture is addressed via a dissipative kinetic law which instills rate dependence and viscous resistance to propagation. A dependence of kinetic viscosity on triaxiality for locally compressive stress states is proposed. Solutions are derived to one-dimensional problems for an isotropic material, linear or nonlinear elastic, under different loading protocols: uniaxial stress extension, uniaxial stress compression, and uniaxial strain compression. Analytical results enable determination of parameters and verification of finite element predictions. Three-dimensional simulations of polycrystalline microstructures are enacted under similar loading protocols. Results provide insight into effects of crystalline microstructure and anisotropy for different stress states. With increasing confinement, the ratio of macroscopic pressure to shear stress increases, and influences of microstructure and anisotropy on average stress and ductility are reduced.

Structure and Magnetism of Iron-Substituted Nickel Hydroxide Nanosheets

Nanosheets composed of stacked atomic layers exhibit unique magnetic, electrical, and electrochemical properties. Here, we report the effect of iron substitution on the structure and magnetism of nickel hydroxide, Ni(OH)2, nanosheets. Ni(OH)2 and iron-substituted Ni(OH)2 (5, 10, 20, and 50 atomic % Fe substitution) were synthesized using a rapid microwave-assisted hydrothermal process. Scanning and transmission electron microscopy show the materials are polycrystalline nanosheets that aggregate into micron-sized clusters. From X-ray diffraction characterization, iron substitutes into the α-Ni(OH)2 lattice up to 20 at. % substitution. The nanosheets exhibit different in-plane and through-plane domain sizes, and Fe substitution affects the nanocrystallite shape anisotropy. The magnetic response differs with Fe substitution: 0% and 5% Fe are ferromagnetic, while samples with 10% and 20% Fe are ferrimagnetic. The competing interactions between magnetization sublattices and the magnetic anisotropy due to the crystalline and shape anisotropy of the nanosheets lead to magnetization reversal at low temperatures. The correlation between higher coercivity and larger nanocrystalline size anisotropy with higher Fe % supports that magnetic anisotropy contributes to the observed ferrimagnetism. The interplay of morphology and magnetic response with Fe-substituted Ni(OH)2 nanosheets points to new ways to influence electron interactions in layered materials which has implications for batteries, catalysis, sensors, and electronics.

Hot-spots in polycrystalline [formula omitted]-tetramethylene tetranitramine ([formula omitted]-HMX): The role of plasticity and friction

We study the effect of the crystalline anisotropy and the relative importance of plasticity and friction on the formation of hot-spots in polycrystalline and single crystal β-HMX when impacted at different weak shock strengths with particle velocities 0.1 km/s and 0.4 km/s. We use a continuum model for large deformations that includes an equation of state, single crystal plasticity, fracture evolution, and heat transport. Our results indicate that plastic dissipation creates heterogeneous temperature fields due to crystal anisotropy. At high shock strengths, the temperature due to frictional heating at crack surfaces becomes the critical hot-spot formation mechanism for the conditions and parameters studied here. Furthermore, the predicted temperature is more sensitive to changes in the friction coefficient than the Taylor–Quinney coefficient accompanying the plastic dissipation used in the thermal transport equation.

Enhancement of magnetic properties of Sm-Co nano composite ribbons by heavy lanthanide doping

Sm-Co magnets becoming more and more interesting among research community since 1950′s due to its essential role in space and transport industry to be used in some precious instruments such as, sensors, actuators, motors, and gyroscope. The combination of Rare-earth (RE) and Transition metal (TM) is an ideal combination to make a high-performance magnet, as the RE provides the high magneto crystalline anisotropy (HA) and the TM provides the high magnetization (Ms) and high Curie temperature (Tc). SmCo5 compound possesses Tc as high as ∼ 700 °C. Previous studies have reported that HRE (Gd, Dy, Er and Ho) could be used as a temperature compensation material as unpaired 4f electrons in shell gives rise to maximum magnetic moment. In this study, effect of lanthanides (HREs - Gd and/ Dy) on microstructure and magnetic properties of Sm-Co-based rapidly solidified alloy ribbons have been reported. Phase analyses confirmed the presence of 1:5H phase which was prevalent along with a fraction of 2:17R phase in all the alloy ribbons. Hc value was increased from 10.9 to 13.3 kOe (1.09 to 13.3 T) and Br value was increased from 12.5 to 16.2 kG (1.25 to 1.62 T) with Dysprosium addition.

Synthesis of Superhydrophobic Barium Hexaferrite Coatings with Low Magnetic Hardness.

Using the multifunctional material barium hexaferrite as an example, the prospects for treatment at a quasi-equilibrium low temperature in an open atmosphere to form superhydrophobic magnetic coatings with pronounced crystalline and magnetic anisotropy have been demonstrated for the first time. The relationship between plasma treatment conditions, structural-phase composition, morphology, and superhydrophobic properties of (0001) films of barium hexaferrite BaFe12O19 on C-sapphire is studied. X-ray photoelectron spectroscopy (XPS), X-ray diffractometry (XRD), scanning electron microscopy (SEM), atomic force microscopy (AFM), as well as magnetometry and moisture resistance analysis, were used as research methods. During plasma treatment with a mass-average temperature of 8-10 kK, intense evaporation and surface melting were observed, and texturing of the deposit along (0001) is found. When the treatment temperature was reduced to 4-5 kK, the evaporation of the material was minimized and magnetic and crystal anisotropy increased. However, the increase in the size of crystallites was accompanied by the transition of oxygen atoms from lattice nodes to interstitial positions. All samples exhibited low coercive fields below 500 Oe, associated with the frustration of the magnetic subsystem. Features of growth of materials with a wurtzite structure were used to form a superhydrophobic coating of barium hexaferrite. Plasma treatment regimes for obtaining self-cleaning coatings are proposed. The use of magnetically hard barium hexaferrite to radically change the properties of a coating is demonstrated herein as an example.

Influence of oxygen and nitrogen doping on the structure and magnetic properties of CoNi alloy: First principle calculations

We have studied the effects of oxygen and nitrogen doping as interstitial defects on the structure and magnetic properties of CoNi alloy using the first principle density functional theory, where we include the orbital-spin interaction in the calculations. Our calculations reveal that the CoNi:ONi in the L10-structure has a large enhancement in the saturation magnetization (Ms) and a small reduction in the magnetic crystalline anisotropy (MCA). For CoNi:OCo, we found a small reduction in Ms and MCA. However, for CoNi:NCo and CoNi:NNi there is always a reduction in Ms and MCA. Therefore, the first alloy could be suitable for permanent magnets. A detailed analysis of other parameters, such as the magnetic hardness parameter (κ), optimum supercell parameters, anisotropy field (Ha), and formation energy (Efor) is presented. The interstitial oxygen doping enhances the magnetic properties.

Optimizing the energy product of exchange-coupled soft/hard Zn0.2Fe2.8O4/SrFe12O19 magnets

Permanent magnets based on ferrites are currently studied as possible alternatives, in several application areas, to rare-earth-based magnets to overcome the barriers of high costs, unavailability, and environmental impact. Their attractiveness lies in the large crystalline anisotropy, ensuring resistance to demagnetization, and the possibility of having their modest saturation magnetization enhanced through exchange-coupling with a compatible soft magnetic material of higher saturation magnetization. Using analytical calculations, a micromagnetic finite element model, and comparison with measurements on a produced sample, the conditions that give the highest possible maximum energy product are determined for ferrite-based exchange-coupled Zn0.2Fe2.8O4/SrFe12O19 soft/hard nanocomposite magnets. Two geometries are considered: a spherical core–shell geometry and a composite granular microstructure. Two sets of material parameters are considered for the granular structure, one from the literature and one obtained by fitting to the measured magnetization data. The results show that it is important to have a well-aligned easy axis of hard grains and that the optimal amount of the soft material depends on the alignment of the hard grains as well as their size, with smaller grains yielding larger (BH)max values. The core–shell model shows that the maximum (BH)max can be strongly enhanced, from ∼40 to ∼60 kJ/m3, by using a hard core diameter of <30 nm and a soft shell thickness of <7 nm. The composite granular structure yields a maximum (BH)max of ∼50 kJ/m3 for a soft volume fraction of 43%.

Elimination of the skyrmion Hall effect by tuning perpendicular magnetic anisotropy and spin polarization angle

The skyrmion Hall effect has been regarded as a critical issue in skyrmion future applications, which indicates that it causes skyrmions to deviate from the direction of the driving force and leads to the destruction of skyrmion at the sample edge. In the meanwhile, perpendicular magnetic anisotropy is a promising method to manipulate the skyrmion motion by adding a material with high crystalline anisotropy into an existing material. It has been also investigated that spin polarization angles also have an influence on the skyrmion motion directions. Here, we statistically study a bilayer nanostructure, where the skyrmion Hall effect would be eliminated by modifying perpendicular magnetic anisotropy coefficients and spin polarization angles. Our results may provide a useful method for the design of skyrmion based spintronics devices without skyrmion Hall effect, to meet the need for future high-density information storage applications.

Synthesis of Substituted Barium Ferrites and Hexaferrites and Their Electrochemical Characterization

Magnetic nanoparticle has been an attractive area of research in view of their unique physical and chemical properties. [1] In the field of electrochemistry, particularly electroanalysis, they are extensively used as functional materials due to their high surface area, mass transport, catalytic effect, and control over the local environment. Barium based ferrites have emerged as attractive materials of interest due to their interesting physical, chemical, magnetic and electrical properties. [2] Hexaferrite and ferrites such as barium ferrite are very important group of magnetic oxides and these are used in different technologies including sensors because of their specific properties such as low cost, corrosion resistance chemical stability and large magneto crystalline anisotropy. [3] However, the investigation of the effect by various other elements on the structure of hexaferrite and ferrite particles and its electrochemical properties remains the subject of popular research. In this work, mixed metallic oxides hexaferrite and ferrite were synthesized by sol–gel combustion route using glycerin as an adjuvant. [4] Their structure was confirmed by means of X-ray powder diffraction. Scanning electron microscopy were used to investigate the morphology of the sample and the vibrations of the functional groups were determined by Raman and IR-ATR spectroscopy. The electrochemical behavior of substituted hexaferrite and ferrite were determined by cyclic voltammetry using an Ag/AgCl electrode, platinum wire and a glass carbon electrode (GCE), as reference electrode, counter electrode and working electrode, respectively. The GCE was modified with mixed metal oxides obtained to analyze their electrochemical behavior.Bibliographic Xueli X, Wei S 2019 Materials Technology, 1-5Kefeni, K.K.; Msagati, T.A.; Mamba, B.B. 2017, Sci. Eng. B. 215, 37–55Valenzuela R, Magnetic Ceramics, Chemistry of Solid State Materials 4 serie. Cambridge (Great Britain): Cambridge University Press, 1994, p. 50Sandra F. Basante-Delgado, Dalliver González-Vidal, Jimmy A. MoralesMorales, William A. Aperador-Chaparro, Jairo A. Gómez-Cuaspud, 2020 Phys.: Conf. Ser. 1541 012013

The angle dependent ΔE effect in TiN/AlN/Ni micro cantilevers

In this work, magnetoelectric MEMS sensors based on a TiN/AlN/Ni laminate are investigated for the first time in regards of the anisotropic elastic properties when using hard magnetic Nickel as magnetostrictive layer. The implications of crystalline, uniaxial and shape anisotropy are analysed arising from the anisotropic Δ E effect in differently oriented cantilevers with 25 µm length and 15° spacing. The Δ E effect is derived analytically to consider the angular dependency of the different anisotropies within the sensors. In the measured frequency spectra complex profiles are observable consisting of contributions from neighbouring structures which are connected by a common electrode. The crosstalk effect is strongly depending on the cantilever orientation and reflects the anisotropic mechanical properties of the material stack. The intensity of the crosstalk effect is increasing for shortened cantilevers and narrowing distance between structures. The Δ E effect is investigated based on cantilevers of different angular spacing and of a single cantilever that is rotated in the magnetic field. The derived peak sensitivities are reaching values of 1.15 and 1.31 T −1 . The angular dependency of the sensitivity is found to be approximately constant for differently oriented cantilevers. In contrast, for a singly rotated cantilever an angular dependency of the 4th order is observed. • Δ E effect related eigenfrequency change can be described by uniaxial magnetic anisotropy. • sensitivity differs for single rotated cantilever compared to differently oriented ones. • observed crosstalk effect is depending on structure length, orientation and spacing.

A systematic study of physical properties of La substituted Sr3Co2Fe24O41 Z-hexaferrites

The impact of La substitution has been explored systematically in the present work, it covers a rough scan of the range of solubility of Lanthanum in the Sr3Co2Fe24O41 (SCFO) structure. The La substituted Z-type hexaferrites Sr3-xLaxCo2Fe24O41, with x = 0.00, 0.15, 0.30, and 0.45, have been prepared via solid-state reaction route and named as SCFO, SLCFO5, SLCFO10 and SLCFO15 respectively. The structure and particle morphology of the samples have been investigated via variety of structural characterization methods like X-ray diffraction (XRD), Transmission Electron Microscopy (TEM) and Scanning Electron Microscopy (SEM). A substantial change in structural properties beyond x ≥ 0.45 suggests that their exists a limit of Lanthanum solubility in the Sr3-xLaxCo2Fe24O41 which is x = 0.45. The dielectric properties (ε′ & ε′′) of SCFO, SLCFO5, SLCFO10 and SLCFO15 were examined by varying temperature from 313 to 613 K in the frequency range of 500 Hz to 10 MHz. The dielectric responses of all the samples are frequency-dependent and thermally stimulated, with relaxation-type dielectric behavior. From M-H loops, it has been observed that with increasing La substitution, the saturation magnetization value reduces from 63.85 to 59.17 emu/g, whereas coercivity increases from 109.74 to 450.51 oersted, indicating an increase in magnetic hardness. The saturation magnetization (Ms) and Magneto crystalline anisotropy constant (K1) were calculated by fitting the experimental data. A weak signature of magneto-electric coupling is observed by employing an indirect method in the SCFO sample.

Magnetic anisotropy in two-orbital models

Motivated by the recent first-principle discovery of giant perpendicular magnetic anisotropy (PMA) in Fe/III–V nitride thin films, we theoretically study magnetic crystalline anisotropy(MCA) in a series of lattices with trigonal symmetry. Due to the trigonal crystal field, MCA in these lattices is dominated by first-order perturbation of the spin–orbit coupling (SOC) in the atomic limit, instead of second-order in conventional transition metal materials. In particular, the proportionality between MCA and SOC is robust in Kagome and pyrochlore lattices due to the flat bands therein. While in triangle lattice the second-order relation is restored under the bandwidth effect. These findings give rise to a new understanding of magnetic anisotropy and provide a guide for the future hunting of high PMA materials.

The role of Co2+ cation addition in enhancing the AC heat induction power of (CoxMn1–x)Fe2O4 superparamagnetic nanoparticles

The physical role of magnetically semi-hard Co2+ cation addition in enhancing the AC heat induction temperature (T AC) or specific loss power (SLP) of solid (Co x Mn1−x )Fe2O4 superparamagnetic iron oxide nanoparticles (SPIONPs) was systematically investigated at the biologically safe and physiologically tolerable range of H AC (H AC,safe = 1.12 × 109 A m−1 s−1, f appl = 100 kHz, H appl = 140 Oe (11.2 A m−1)) to demonstrate which physical parameter would be the most critical and dominant in enhancing the T AC (SLP) of SPIONPs. According to the experimentally and theoretically analyzed results, it was clearly demonstrated that the enhancement of magnetic anisotropy (K u )-dependent AC magnetic softness including the Néel relaxation time constant τ N (≈τ eff , effective relaxation time constant), and its dependent out-of-phase magnetic susceptibility primarily caused by the Co2+ cation addition is the most dominant parameter to enhance the T AC (SLP). This clarified result strongly suggests that the development of new design and synthesis methods enabling to significantly enhance the K u by improving the crystalline anisotropy, shape anisotropy, stress (magnetoelastic) anisotropy, thermally-induced anisotropy, and exchange anisotropy is the most critical to enhance the T AC (SLP) of SPIONPs at the H AC,safe (particularly at the lower f appl < 120 kHz) for clinically safe magnetic nanoparticle hyperthermia.

Crystalline orientation and anisotropy of semi-polar GaN films grown on m-sapphire substrate by hydride vapor phase epitaxy

In this paper, semi-polar (10–13) and (11–22) GaN layers were fabricated on m-plane sapphire templates by vertical hydride vapor phase epitaxy system. The GaN layer with a thickness of 10 μm, excluding the thickness of the template. By systematically optimized growth parameters, high quality semi-polar layers were achieved and confirmed by high resolution X-ray diffraction (HR-XRD) measurement, with a rocking curve width of 0.15° for (10–13) GaN layer and 0.31° for (11–22) GaN layer. In-plane epitaxial relationships between (10–13) or (11–22) GaN and sapphire substrates were also determined by HR-XRD. Crystalline anisotropies were shown in two aspects. One is associated with the crystal quality, which can be measured by the full width at half maximum (FWHM) value curves on azimuth Phi angles and originated from the different atom mobility along different crystal directions on growing surface. The other one is associated with defects on the surface, which can be clearly recorded by optical cameras. When defects of epitaxial films accumulate, the shape of FWHM curves dependence on Phi degree changed from M−type to W-type. These two kinds of anisotropic features are closely connected with each other.

Influence of Gd content on the structural, Raman spectroscopic and magnetic properties of CoFe2O4 nanoparticles synthesized by sol-gel route

The structural and magnetic properties of sol-gel synthesized Gd doped (x = 0.00 to 0.15) CoFe2O4 nanoparticles (NPs) have been studied. The x-ray diffraction (XRD) and FTIR spectroscopy along with Raman spectra confirmed the formation of face centered cubic inverse spinel structure. TEM images showed the NPs are well-dispersed with average particle size 30 nm. Room temperature magnetic measurement showed the value of coercivity fluctuates from 353 Oe to 1060 Oe for different % of Gd content. The maximum coercivity, saturation magnetization, magnetic moment, magnetic anisotropy, remnant magnetization found for 0.03% Gd content are 1060.19 Oe, 77.53 emu/gm, 3.29 μ, 4.11 × 104 erg/cm3, 32.38 emu/gm, respectively. The large value of coercivity indicated that the interparticle interactions and crystalline anisotropy are high. Thus CoFe2-xGdxO4 magnetic NPs might be a potential candidate for data processing, automotive and telecommunications.

F+ center exchange mechanism and magnetocrystalline anisotropy in Ni-doped 3C-SiC

• F + center exchange mechanism has been invoked in order to explain the long range magnetic order in the system. • The Curie temperature is found to be above 350 K for all the doped samples obtained from the modified Bloch’s T 3/2 law. • The dynamic nature of the BMPs sizes have been studied extensively using Hc vs T data. • The spontaneous spin polarization has been induced in the system due to strong hybridization between (C) 2p and (Ni) 3d orbital. • The decrease in magneto crystalline anisotropy constant value with increase in temperature essentially indicates the weakening of the magnetic interaction in the system. • The incomplete quenching of orbital angular momentum and partial removal of orbital degeneracy resulted in reduction of line width and enhancement of integrated intensity as the temperature rises. Towards the development of a magnetic semiconductor suitable for spintronic device applications in extreme environments, we explored the possibility of inducing magnetic interaction in SiC by doping Nickel. The X-ray diffraction and Raman Spectroscopy studies confirm the incorporation of Ni into the host lattice. The magnetic measurements and electron spin resonance studies indicate the presence of room temperature ferromagnetic interaction in the system. The Curie temperature of 1, 3, and 5% Ni-doped samples have been found to be 420 K, 520 K, and 540 K respectively. Electron spin resonance study reveals that the valence state of Ni is 2 + , which implies the creation of vacancies at both Silicon (V Si ) and Carbon (V C ) sites as they are tetravalent. The change in magnetization of the system with an increase in dopant concentration is consistent with the variation in the number of vacancies and free holes. The analysis of magnetization data using the Law of approach to saturation shows that the anisotropic constant decreases with an increase in temperature. The long-range magnetic interaction in the system is explained using the F + center exchange mechanism.

Low-energy electronic structure of perovskite and Ruddlesden-Popper semiconductors in the Ba-Zr-S system probed by bond-selective polarized x-ray absorption spectroscopy, infrared reflectivity, and Raman scattering

Chalcogenides in perovskite and the related layered Ruddlesden-Popper crystal structures (chalcogenide perovskites for brevity) are an exciting family of semiconductors but remain experimentally little studied. Chalcogenide perovskites share crystal structures and some physical properties with ionic compounds such as oxide and halide perovskites, but the metal-chalcogen bonds responsible for semiconducting behavior are substantially more covalent than in these more-studied perovskites. Here, we use complementary experimental and theoretical methods to study how the mixed ionic-covalent Zr-S bonds support the electronic structure and physical properties of perovskite ${\mathrm{BaZrS}}_{3}$ and Ruddlesden-Popper ${\mathrm{Ba}}_{3}{\mathrm{Zr}}_{2}{\mathrm{S}}_{7}$. We apply theoretical methods to assign features of experimentally measured x-ray absorption spectroscopy (XAS) to particular orbital transitions, enabling a clear physical interpretation of angle-dependent, polarized XAS data measured on single-crystal samples, and an atomistic view of the covalent bonding network that facilitates charge transport. Polarized Raman measurements identify signatures of crystalline anisotropy in ${\mathrm{Ba}}_{3}{\mathrm{Zr}}_{2}{\mathrm{S}}_{7}$ and enable the first assignments of mode symmetry in this material. Infrared reflectivity reveals electronic transport properties that augur well for the use of chalcogenide perovskites in optoelectronic and energy-conversion technologies.