Superexchange Research Articles

Synthesis, characterization and magnetic behaviors of La1-xCsxMnO3 (0 ≤x ≤ 0.1) ceramics

In this paper, we focus on the Cs-doping effect at the La-site in La1-xCsxMnO3 (x = 0; 0.05 and 0.1) manganite. Synthesized powders via the sol-gel auto-combustion route have been characterized by structural and magnetic measurements. All samples crystallize into a rhombohedral structure with R 3‾ c space group as confirmed by Rietveld analysis of the X-ray diffraction (XRD) patterns. The diffraction analyses as function of temperature reveal a linear evolution of the structural parameters influencing the Jahn-Teller (J-T) distortion. Spherical nanoparticles have been observed by scanning electron microscopy (SEM). The energy-dispersive X-ray spectroscopy (EDS) analyses confirmed the expected presence of La, Cs, Mn and O ratio, as well as the phase purity of the synthesized materials. The polycrystalline grain structure was confirmed by transmission electron microscopy (TEM), where crystallite size obtained from TEM ranges from 21 nm to 120 nm as function of the composition and sintered temperature. The lattices fringes resolved in the high-resolution TEM (HRTEM) images confirmed the crystal rhombohedral symmetry of our compounds. X-ray photoelectron spectroscopy (XPS) studies demonstrate the mixed valence states of manganese ions (Mn4+ and Mn3+) in undoped as well as doped systems. The electron spin resonance (ESR) analyses confirmed the decreasing of the ferromagnetic ordering versus the increase of Cs doping. Soft ferromagnetism has been observed in all our La1-xCsxMnO3 (x = 0; 0.05 and 0.1) samples which can be attributed to the super exchange interaction between the magnetic ions. Surprisingly enough, the magnetization behavior is found to be a sum of ferromagnetic (FM), superparamagnetic (SPM) and paramagnetic (PM) contributions at low temperature (i.e. 4K). As expected, their behavior is PM at room temperature. This work shows how structural and magnetic properties can be greatly affected by small amount of La-substitution by Cs.

Single–crystalline LiNi0.8Co0.1Mn0.1O2 stabilized by F–doping–induced superlattice for 4.8 V lithium–ion batteries

Single–crystalline Ni–rich ternary layered oxides represent the cutting–edge cathode materials for lithium–ion batteries, offering enhanced cycling stability compared to the polycrystalline counterparts by eliminating grain boundaries. However, their structural stability encounters a significant challenge when operated under high voltages (cut–off charging potential ≥ 4.6 V). Excessive extraction of Li+ ions can lead to the localized collapse of transition metal (TM) slabs and accumulation of lattice dislocations, which hinders Li+ diffusion and eventually cause capacity decay. This study demonstrate that the introduction of F dopants triggers an ordered mixing of Li+ and Ni2+ ions to form a superlattice in single–crystalline LiNi0.8Co0.1Mn0.1O2. This unique F–doping–induced superlattice stabilizes the deintercalated structure through Ni2+ (Li layer)–O2––Ni2+ (TM layer) interlayer super–exchange strong interactions, thereby facilitating the reversible H2–H3 phase transformation during cycling. Consequently, when cycled between 2.8–4.8 V at 1C, the F doped single–crystalline LiNi0.8Co0.1Mn0.1O2 exhibits unprecedented cycling stability, retaining 90.3 % of its initial capacity after 200 cycles, while achieving a high discharge capacity of 186.8 mAh/g and an impressive energy density of 706.5 Wh/kg. This work sheds light on the microstructural engineering for Ni–rich layered cathode materials.

Tailoring Bi1−x−yBaxFeyFeO3 for desired properties: insights into structural, dielectric, and magnetic responses

In present study, samples of Bi1−x−yBaxFeyFeO3 have been synthesized, where x = 0.15, y = 0; x = 0.10, y = 0.10; and x = 0.15, y = 0.10 utilizing a swift two-stage solid-state reaction method. X-ray diffraction (XRD) data has been Rietveld refined to evaluate the structural parameters. Micro-strain is also calculated using Williamson Hall method. Temperature (300 K to 660 K) dependent measurements of the dielectric constant have been conducted at various frequencies (100 kHz, 500 kHz, and 1000 kHz). The dielectric constant (ε′) rises as the temperature increases. Two dielectric anomalies around 450 K and 613 K have been noticed in ε′ versus T curves for all the samples which might be related with defect dipoles and the magnetic transition respectively. Further, an insignificant value of loss tangent (0.2) specifically at around 300 K is a signal of small leakage current in the samples. The source of high dielectric constant is discussed by considering the structural distortions in the ceramics. A clear hysteresis loop has been observed for all the samples which is a sign of collapse of antiferromagnetic nature of BiFeO3. Further, in case of co-doped samples, almost a saturation in magnetization with magnetization value 5.9718 emu g−1 has been noticed in hysteresis curve indicating a major contribution of ferromagnetic interaction. Enhancement in the net magnetization is briefly discussed by considering the ferromagnetic type direct interaction among Fe3+ ions and suppressing the anti-ferromagnetic type super exchange interaction.

Reduced A–B super exchange interaction in zirconium doped cobalt ferrite due to laser irradiation

The impact of Nd:YAG laser irradiation and the addition of zirconium ions (Zr4+) on the physical properties of CoFe2O4 spinel nano-ferrites has been studied. The co-precipitation method was used to synthesize the samples. X-ray diffraction (XRD) and high-resolution transmission electron microscopy (HRTEM) were employed to examine the structure and morphology. The decrease in the Curie temperature Tc is due to the laser irradiation and the increase in the Zr content of the sample. This decline in Tc is a result of an increase in the canting of the spins, leading to a change in the thermal energy needed for compensate the spin alignment. The difference in the Tc between the non irradiated and the irradiated samples is about 7%, 43% and 34% for CoFe2O4, Co1.1Zr0.1Fe1.8O4, and Co1.3Zr0.3Fe1.4O4, respectively. The decrease in the coercivity of the laser irradiated sample is due to a reduction in the magnetic anisotropy and an altered distribution of the cations (Co2+, Fe3+, Zr4+). The observed trend indicates that laser irradiation, and Zr substitution, can be used to modify the magnetic hardness of the samples. The low coercivity of irradiated Co1.1Zr0.1Fe1.8O4 makes it suitable for a range of applications. The high-frequency response of the Co1+xZrxFe2–2xO4 NPs shows that they can operate within the frequency range of 7.5 GHz–11.56 GHz.

Investigation of optical and magnetic properties of 3d-4d transition metal ion based double Perovskite: Sr2MnRuO6

Investigation of physical properties in double perovskites, A2B′B″O6, containing 3d/4d transition metal ions at the B sites is an interesting avenue of research. In this study, we focus on Sr2MnRuO6, exploring its structural, morphological, optical and magnetic properties. Sr2MnRuO6 was synthesized in single phase using solid-state reaction route. It crystallizes in a tetragonal structure (space group I4/mcm, #140) with lattice parameters a = 5.4633 (2) Å, c = 7.9419 (1) Å. X-ray diffraction analysis revealed no super lattice reflections, indicating disorder in the B-site cations.The Jahn-Teller distortion in Mn-O6 octahedra,as revealed by XRD results, indicates a high spin state for the Mn3+ ion. The stoichiometric ratio of Sr: Mn: Ru (∼2:1:1), as determined by bond valence sum calculations and confirmed by energy dispersive x-ray spectroscopy agree well with the nominal composition of Sr2MnRuO6. Diffuse reflectance spectroscopy showed strong absorption throughout the visible region with a direct band gap of ∼3 eV, indicating Sr2MnRuO6 is a potential candidate for optical applications. Huge photoluminescence emission observed in the visible region is attributed to Mn3+ ions. The temperature dependence of molar susceptibility data indicates a paramagnetic to antiferromagnetic transition around 195 K. The possible super exchange paths for antiferromagnetic interaction are Ru5+- 4d3 (t2g3eg0) − O1 − Ru5+- 4d3 (t2g3eg0) along the z axis, or Ru5+- 4d3 (t2g3eg0) − O2 − Ru5+- 4d3 (t2g3eg0) in the xy-plane, with the angles between these orbitals being nearly 180°. At low temperatures under a 10,000 Oe field, spin glass type magnetic behaviour is observed. The effective magnetic moment (6.17 μB) obtained from the Curie-Weiss fit from 260 K to 290 K nearly matched with the theoretical resultant effective moment (6.24 μB) by considering Mn3+ ions in HS state and Ru5+ ions.Specific heat measurements revealed no long-range magnetic ordering down to 2 K, further suggesting the role of cationic disorder in the magnetic behaviour of Sr2MnRuO6.

Investigation of magnetic exchange interactions in Cr-doped Ca0.5Sr0.5RuO3

The value of Curie temperature (T C) and resistivity for Ca0.5Sr0.5Ru1−xCrxO3 are found to increase with increase in x from 0 to 0.1. The T C increases from 38 K to 107 K. In this work, we investigate the increment using spin polarised density functional theory. The compounds exhibit Griffiths phase. Our results show that to understand the behaviour of the increase in T C , it is important to consider not only the competing super exchange and super–super exchange interactions between Ru/Cr–Ru/Cr ion pairs but also the increment in the value of the magnetic moment due to the localized character of the dopant (Cr) ion. Our results suggest that the increased resistivity with Cr doping could be due to increased scattering rate and strong on-site coulomb repulsion due to Cr doping. It is also important to note that the behaviour of T C with the Ru–O–Ru bond angle is not in line with the functional form reported for ferrites, chromites and some ferromagnetic oxides. We believe that our results will be helpful in further exploring the origin of magnetism and transport on Cr doping in perovskite ruthenates.

Fingerprints of the Jahn-Teller and superexchange physics in optical spectra of manganites

Transition metal oxides incorporating Jahn-Teller (JT) ions Mn3+ (3d 4) in manganites and Cu2+ (3d 9) in cuprates exhibit outstanding magnetic and electronic properties, including colossal magnetoresistance (CMR) and high-temperature superconductivity (HTSC). The physics of these compounds is associated with the orbitally-degenerate electronic states of JT ions, leading to the linear electron-lattice interaction, complemented by the entirely electronic superexchange (SE) interaction. Here, we discuss the fingerprints of the JT and SE physics in the temperature-dependent complex dielectric function spectra and multi-order Raman scattering spectra measured in a detwinned LaMnO3 crystal, which is a famous compound exhibiting cooperative JT effect, being also a progenitor of magnetic materials exhibiting CMR effect. In accordance with the obtained experimental evidence, the associated effective parameters characterizing the JT and SE physics in manganites are presented.

Investigation of structural phase stability, modified magnetic spin order and low temperature spin glass-like phase transitions in Sc-doped M-type BaFe12O19 hexaferrite

This work used two approaches of mechanical alloying before high temperature solid state reaction to synthesize BaFe12-xScxO19 (x = 0.5 to 6.0) system. Rietveld refinement of X-ray diffraction patterns showed the formation of extra phases at higher Sc doping, along with the main magnetoplumbite structure. Raman spectroscopy suggested random distribution of Sc ions at the Fe-sites of hexaferrite structure. X-ray photoelectron spectroscopy (XPS) confirmed the +3 charge state at the Fe/Sc-sites. The Fe 3s band suggested dilution of ferromagnetic 3s-3d spin exchange interactions. The neutron diffraction study re-confirmed random occupancy of the non-magnetic Sc3+ ions at Fe3+ sites of the Sc doped Ba hexaferrite system. The transformation of magnetic spin order from collinear to non-collinear state has shown spin glass-like features at low temperature regime in the dc magnetization curves. This is an effect of dilution of Fe–O–Fe ferrimagnetic super exchange interactions and spin frustration in Sc-doped samples.

Two-dimensional monolayer CrGaS3: A ferromagnetic semiconductor with high Curie temperature and tunable magnetic anisotropy

Two-dimensional (2D) intrinsic ferromagnetic (FM) materials are promising candidates for fabricating next generation high-performance spintronic devices. However, all experimentally verified 2D FM semiconductors have Curie temperature (Tc) far below room temperature, which hinders their practical applications. Based on first-principles calculations, a stable and previously undiscovered 2D CrGaS3 structure is predicted, which is a semiconductor with an indirect bandgap of 1.99 eV and displays out-of-plane magnetic anisotropy. More importantly, it exhibits high-temperature ferromagnetism, with Tc ranging between 520 and 814 K. The high Tc is attributed to the presence of both direct-exchange and super-exchange interactions that are ferromagnetic, along with the eg-px/py-eg super exchange having a zero virtual exchange gap. Furthermore, it has been observed that the magnetic anisotropy can be tuned by external strain. These findings indicate its potential as a promising candidate for the rapid development of 2D spintronic applications.

Investigation of conventional exchange bias in (Nd1-xHox)2CoMnO6 (x = 0.0–0.4) double perovskite

In this article, we have investigated the characteristics related to structure, magnetism and exchange bias behavior in single phased polycrystalline samples of (Nd1-xHox)2CoMnO6 (x = 0.0–0.4) (NHCMO) series. The samples were prepared using the conventional solid state reaction technique and they crystalize in monoclinic structure with P21/n space group. The x = 0.0 sample shows the ferromagnetic transitions at TC1 = 139K and TC2 = 170K. These values decrease to 136K and 160K respectively for x = 0.1 sample. However, for other Ho substituted samples we observed only one transition. For x = 0.2, TC is 129K which decreases to 118K for x = 0.4 sample. The ferromagnetic super exchange interaction that arises within the network of Co2+ and Mn4+ ions bridged by O2− ions is the reason of occurring of these transitions. The presence of anti-site defects with antiferromagnetic interactions and subsequent formation of anti-phase boundaries within the system cannot be ignored. To gain a deeper insight into the underlying magnetic interactions, the M − T plots, under both the ZFC and FC conditions, were measured by applying different external magnetic fields. Saturation magnetization (MS) value of 3.68 μB/f.u. is observed in parent sample. The MS value increases to 7.22 μB/f.u. for x = 0.4 sample. Such mixed magnetic ground state of the samples motivates us to perform the exchange bias field measurement revealing an exchange bias field of 725Oe is found for x = 0.0 sample at 5K.

Engineering and analysing the super exchange interaction of Fe3+- O2− - V5+ on novel multiferroic LaFeO3/BiVO4 nanocomposite

Herein, we report an interesting magnetic interaction taking place between the perovskite structured Lanthanum Ferrite (LaFeO3) and scheelite structured Bismuth Vanadate (BiVO4) material. The structural analysis of LaFeO3/BiVO4 nanocomposite was carried out using Rietveld refinement software to understand their stretching and shortening of bond angle and bond length respectively. The visualized crystal structure of the nanocomposite in comparison with that of the pristine compound explains the induced octahedral tilt, confirming the super exchange interaction between Fe3+- O2− - V5+. The electronic configuration of Vanadium 5+ with an empty d-shell and Iron 3+ with a half-filled d-shell satisfies the theory proposed by Goodenough and Kanamori et. al. This might lead to a promising pathway for magnetically driven applications.

Improved magnetic properties of Fe substituted La2CoMnO6 for spintronic applications

A detailed study of magnetic behaviour of double perovskites was carried out by developing La2Co1-xFexMnO6; (x = 0.0, 0.2, 0.5, 0.8 and 1.0) via sol–gel technique. All samples showed single magnetic transition except pure LCMO (x = 0.0) and LCFMO2 (x = 0.5). Temperature dependent inverse magnetic susceptibility (χ-1) was fitted in accordance with Curie-Weiss law. μeff (effective magnetic moment) was determined for all the developed samples. Pure LCMO showed a downward divergence from Curie-Weiss law below 230 K but above transition temperature which indicates the characteristics of Griffiths phase. Saturation magnetization (Ms) increased initially and then decreased, whereas coercive field (Hc) was found to be monotonous decreased with increase in Fe content. LCFMO1 (x = 0.2) was noticed to have maximum Ms (38.87 emu/g) which indicated that the magnetic properties of pure LCMO were improved with Fe substitution, but for lower substitution only. Magnetization vs. field (M−H) curves were not well saturated even at a magnetic field of 60 kOe, therefore, values of Ms for all the samples were estimated using law of approach to saturation. With increase in Fe content, an increased anti-site disorder among Mn and Co strengthened antiferromagnetic (AFM) super exchange interactions and weakened ferromagnetism (FM). Therefore, substitution of Fe on Co-site was responsible for systematic decrease in saturation magnetization when × exceeded 0.2.

Engineering and analysing the super exchange interaction of Fe3+- O2− - V5+ on novel multiferroic BiFeO3/BiVO4 nanocomposite

Herein, we report an interesting magnetic interaction taking place between the Scheelite structured Bismuth Vanadate (BiVO4) and Perovskite structured Bismuth Ferrite (BiFeO3) nanomaterials. The structural tilt in the Fe/V–O6 octahedral site was analysed using Rietveld refinement data. The tilt in bond angle, explains the magnetic contribution of the Fe–O–V interaction because the nanocomposite shows a significant increase in their coercivity and retentivity values. The coercivity value was found to be six times greater than the pristine material. Finally, the resulting weak ferromagnetic behaviour in BiFeO3/BiVO4 by means of Fe–O–V interaction was examined using the first-order derivative (dM/dH) of M − H data. These results suggest that the material can be used for magnetic applications.

The Impact of La Substitution on the Structural, Molecular, Morphological, and Thermal Properties of Mn0.6Zn0.4Fe2O4

The current work involves the use of flash auto combustion procedure to synthesize nano-ferrites Mn0.6Zn0.4LaxFe2-xO4, (x = 0.00, 0.02, 0.04, 0.06, 0.08, and 0.10) annealing at 500 °C for 4 h. X-ray Diffraction (XRD), Fourier transition infrared spectroscopy (FTIR), and high-resolution transmission electron microscopy (HRTEM) were used to characterize the structural properties of produced samples. Scanning electron microscopy (SEM) was utilized to examine the surface morphology of the samples at various Lanthanum concentrations. From XRD, the spinel cubic structure for all samples with few traces of secondary phase at high La concentrations is assured. The crystallite size is estimated to be in the nanoscale range of 13.16–18.13 nm using the Debye–Scherrer formula. The appearance of characteristic vibrational bands near 460 cm−1 and 563 cm−1, which correspond to the octahedral and tetrahedral sites, respectively, confirms the formation of the spinel structure. SEM micrographs show that the grains are nearly irregular in shape, and the accumulation of La+3 ions at the grain boundaries exerts tensile strength and pressure on the grain itself, reducing the grain size. The particle size estimated by TEM coincides well with the crystallite size determined by XRD. The thermogravimetric analysis, (TGA), was used to investigate the thermal properties of the nanoferrites from room temperature to 1000 °C. In comparison to the other samples, the sample with x = 0.04 has greater thermal stability and the TEM measurement indicates that this sample has the smallest particle size. Therefore, we can assert that the thermal stability improves as the particle size decreases. The magnetic permeability was measured in the temperature range 303–773 K at a fixed frequency of 10 kHz and at various La contents. The sample with x = 0.04 has a minimal permeability value, showing that the separation brought on by La ions has diminished the super exchange contact between magnetic ions.

Microstructural Characterization of the Sol-Gel-Derived Sr2CrReO6 Powders and Their Magnetic and Electrical Transport Properties.

The double-perovskite (DP) Sr2CrReO6 (SCRO) oxide has gained much attention due to its high Curie temperature (∼635 K), high spin polarization, and strong spin-orbit coupling, which provides promising potential for room-temperature spintronic devices. In this work, we report on microstructures of a set of sol-gel-derived SCRO DP powders and their magnetic and electrical transport properties. The SCRO powders crystallize into a tetragonal crystal structure (space group of I4/m). X-ray photoemission spectroscopy spectra verify that the rhenium ions possess variable valences (Re4+ and Re6+) in the SFRO powders while chromium ions are presented as Cr3+. Ferrimagnetic behavior was observed in the SFRO powders at 2 K, and the saturation magnetization was evaluated to be 0.72 μB/f.u. and the coercive field to be 7.54 kOe. The Curie temperature was derived from susceptibility measurements to be 656 K at 1 kOe. Such ferrimagnetic behavior stems from the Cr3-Re4+(Re6+) super exchange interaction via intervening oxygen. Electrical transport measurements revealed that the SFRO ceramic grains were semiconducting and the electrical transport process was governed by the small polarons hopping with variable ranges. The hopping paths for these small polarons are provided by the hetero-valent Re ions in the SCRO ceramics. Negative magnetoresistance (MR) was observed in the SCRO ceramics, and the plot of MR vs magnetic field (H) exhibited a butterfly-like shape. The MR (2 K, 6 T) was measured to be -5.3%, due to the intergranular magneto-tunneling effect. The present results demonstrate a unique combination of high-temperature ferrimagnetism and intrinsic semiconducting nature of the sol-gel-derived SCRO oxides, which are highly attractive for oxide spintronics.

Van der Waals Stacked 2D-Layered Co2Ge2Te6 with High Curie Temperature and Large Magnetic Crystal Anisotropy

Co2Ge2Te6 shows an intrinsic ferromagnetic order, which originates from the superexchange interaction between Co and Te atoms, with a Curie temperature of 161 K. The Co2Ge2Te6 monolayer is half-metal, and the spin-β electron is a semiconductor with a gap of 1.311 eV. The Co2Ge2Te6 monolayer shows in-plane anisotropy, with a magnetic anisotropy energy (MAE) of −10.2 meV/f.u., and Te atoms contribute −9.94 meV/f.u. Moreover, the bilayer with AA- and AB-stackings has MAEs of −24.659 and −24.492 meV/.f.u., respectively. Most interestingly, bilayers present ferromagnetic half-metallicity independent of stacking orders. The multilayers (N ≥ 6) present ferromagnetic half metal, while magnetoelectronic properties are related with stacking patterns in thinner multilayers. Moreover, the magnetoelectronic properties of bulk are related with stacking patterns. The multilayers’ magnetic orders are determined by the super–super exchange and weak van der Waals (vdW) interaction. Moreover, the Co2Ge2Te6 monolayer and multilayers show good dynamical and thermal stability. These findings could pave the way of application of intrinsic ferromagnetic Co2Ge2Te6 in the spintronics.

A comparative study on structural, magnetic and optical properties of rare earth ions substituted Bi1−x R x FeO3 (R: Ce3+, Sm3+ and Dy3+) nanoparticles

Abstract A comparative study on the manifestation of rare earth ions substitution induced alteration in structure, magnetic and optical properties of BiFeO3 nanoparticles was done. Sol-gel technique was employed to synthesize Bi1−x R x FeO3 (x = 0.05 and 0.10; R: Ce3+, Sm3+ and Dy3+) nanoparticles. X-ray diffraction patterns and Raman spectra analysis confirmed substitution driven structural phase transformation from distorted rhombohedral structure to orthorhombic structure for x = 0.10 samples. The enhanced magnetic properties with weak ferromagnetic behaviour were observed with increasing concentration of rare earth ions in BiFeO3 nanoparticles. The improved magnetic characteristics are attributed to many factors such as the uncompensated surface spins in nanoparticles, breaking of spin cycloid with R 3+ ions substitution and super exchange interaction between R 3+ and Fe3+ ions. The maximum magnetization values of 1.77 emu g−1, 1.87 emu g−1 and 5.5 emu g−1 were observed for x = 0.10 samples with Ce3+, Sm3+ and Dy3+ substitution, respectively. The magnetization increased with increasing difference in ionic radii of host Bi3+ (1.17 Å) ion and dopant Ce3+ (1.14 Å), Sm3+ (1.08 Å) and Dy3+ (1.03 Å) ions. UV–Visible diffuse reflectance spectra showed a sharp absorption in visible region and energy band gap values variation in the range 2.2 eV–2.33 eV.

Ag(II) as Spin Super-Polarizer in Molecular Spin Clusters.

Using quantum mechanical calculations, we examine magnetic (super)exchange interactions in hypothetical, chemically reasonable molecular coordination clusters containing fluoride-bridged late transition metals or selected lanthanides, as well as Ag(II). By referencing to analogous species comprising closed-shell Cd(II), we provide theoretical evidence that the presence of Ag(II) may modify the magnetic properties of such systems (including metal-metal superexchange) to a surprising degree, specifically both coupling sign and strength may markedly change. Remarkably, this happens in spite of the fact that the fluoride ligand is the least susceptible to spin polarization among all monoatomic ligands known in chemistry. In an extreme case of an oxo-bridged Ni(II)2 complex, the presence of Ag(II) leads to a nearly 17-fold increase of magnetic superexchange and switching from antiferro (AFM)- to ferromagnetic (FM) coupling. Ag(II)─with one hole in its d shell that may be shared with or transferred to ligands─effectively acts as spin super-polarizer, and this feature could be exploited in spintronics and diverse molecular devices.

Pressure dependent magnetic properties on bulk CrBr3 single crystals

The van der Waals class of materials offer an approach to two-dimensional magnetism as their spin fluctuations can be tuned upon exfoliation of layers. Moreover, it has recently been shown that spin-lattice coupling and long-range magnetic ordering can be modified with pressure in van der Waals materials. In this work, the magnetic properties of quasi two-dimensional CrBr 3 are reported applying hydrostatic pressure. The application of pressure up to 0.844 GPa shows a 1.77% decrease in saturation magnetization with a decrease in the Curie temperature from 33.05 to 30.41 K. Density functional theory calculations with pressure up to 1 GPa show a reduction in volume and interplanar distance as pressure increases. To further understand the magnetic properties with applied pressure, the magnetocrystalline anisotropy energy (MAE) and exchange coupling parameter(s) ( J ) are calculated. There is small decrease in MAE and the first nearest neighbor interaction ( J 1 ) ( U = 2.7 eV and J = 0.7 eV) is increasing with respect to increasing pressure. Overall, CrBr 3 displays ferromagnetic interlayer coupling and the calculated exchange coupling and MAE parameters match well with the observations from the experimental work. • Hydrostatic pressure decreases saturation magnetization and curie temperature. • Magnetocrystalline anisotropy energy decreases with increasing pressure. • Super exchange coupling increases with increasing pressure. • Pressure decreases the volume and lattice parameters of the system. • The bond angle between Cr-Br-Cr is decreasing up to 1 GPa.

Computational insights into electronic, magnetic and optical properties of Mn(II)-doped ZnTe with and without vacancy defects

First principles calculations have been performed to investigate the optoelectronic and magnetic properties of Mn(II); ZnTe DMS with and without native defects using first principle calculations. Our results find that anti-ferromagnetic coupling dominates in the pure Mn(II)-doped ZnTe system due to super-exchange (SE) mechanism. The impact of p-type and n-type defects on magnetic coupling in Mn(II)-doped ZnTe were discussed and we found that p-type defect such as Zn vacancy defects play important role in stabilization of FM state due to the formation of bound magnetic polaron (BMP) while n-type defect such as Te vacancy defect does not affect the ground state of Mn(II); ZnTe. The magnetic coupling of Mn(II) spins in the absence and presence of Zn vacancy were explained on the basis of phenomenological band structure model. The optical absorption spectra of pure ZnTe and Mn(II); ZnTe with and without vacancies have been investigated and we found that single Mn(II)-doping in the lattice of ZnTe generates an absorption band at energy around 2.02 eV, which is assigned to intra-band d-d transitions of Mn(II) dopant. The band at energy around 0.44 eV in the absorption spectrum of Mn(II)-doped ZnTe with Zn-vacancy may be due to the acceptor states produced by Zn vacancy at Fermi level and band around 1.6 eV in the spectrum of Te vacancy defect system are related to the donor states produced by Te vacancy defect. Moreover, the correlation of magnetic coupling with intra-band d-d transition bands and fundamental bandgaps of ZnTe were also discussed and it was found that intra-band transition peak of Mn(II) ions and optical band gap of ZnTe are blue-shift in AFM coupled Mn(II) ions and are red-shift in FM coupled ions system. Our present findings highlight the worthwhile half-metallic properties of Mn(II)-doped ZnTe, which can be obtained via Zn vacancy defect engineering; this can find broad applications for the fabrication of optoelectronic and spintronic devices.