Physica B-condensed Matter最新文献

This study focuses on comprehensively investigating the crystal structure, electronic, magnetic and optical properties of pure and Pb-doped CdS at different concentrations using first-principles methods with the GGA-PBE+U approximation. Our calculations successfully reproduce the experimentally observed optimized lattice parameters and band gap values for both pure and Pb-doped CdS systems. Band structure results show a large and significant reduction in the band gap of Pb-doped CdS at low concentrations, followed by a steady increase at high Pb concentrations. The electron density distribution show the covalent nature between Cd-S and Pb-S. The optical properties of pur and Pb-doped CdS show: a significant increase in absorption and in reflectivity in the visible and ultraviolet domains with doping. Finally, a reduction in optical transmission in the visible energy domain. These optical analyzes provide essential information on the behavior of these materials, thus broadening its practical applications, notably in the design of optoelectronic devices.

This study investigates the superconducting and magnetic behaviour of Potassium-doped Cu_0.5Tl_0.5Ba₂Ca₂Cu_3-xK_xO_10-δ superconductors by varying potassium-concentrations (x = 0, 1, 2.5, 3). We have synthesized the samples by two-step solid-state-reaction method and explored their superconducting features by XRD analysis, SEM and resistivity measurements. Through a comprehensive exploration of magnetic measurements i.e magnetization versus magnetic field and temperature, we aim to elucidate the impact of potassium doping on the diamagnetic characteristics of these superconductors. The results reveal that by raising the doping concentration of potassium, the orthorhombic unit cell's axis lengths decresese. The onset of superconductivity and the magnitude of diamagnetism are also decreased. The magnetic behavior of these samples was studied by field cooled and zero field cooled from 2 to 300 K and taking the hysteresis loops at temperatures 2 to 60 K. In the doped samples, the suppression of current density is steeper with increase in temperature. Doped atoms boost the population of localized defects, which serve as pinning centers. This study will contribute valuable information to the understanding of the relationship between magnetic behavior and the superconducting nature of complex oxide materials.

In this paper, we comprehensively investigate the isothermal magnetization behavior of doped perovskite manganite nanoparticles. The focus is on understanding the impact of variation of particle sizes on the soft and hard magnetic phases with respect to the changes in the coercive field and remanent magnetization, both theoretically and experimentally. The study seeks to correlate experimental findings with the proposed phenomenological model to gain deeper insights into the underlying mechanisms governing exchange coupling and anisotropy effects in the nanocrystalline composites. The proposed phenomenological model beautifully demonstrates how the values of saturation magnetization and coercive field changes with changing the particle size in the nanocrystalline La_0.48Ca_0.52MnO${}_3$ (LCMO48) and La_0.46Ca_0.54MnO${}_3$ (LCMO46) compounds. In addition, the model provide an insights into the limitations of critical radius, size and shape of the nanocrystalline particle. This investigation looks into how the size of particles affects their magnetic properties, specifically coercive field and remanent magnetization.

The inverse spin Hall effect (ISHE) is a significant phenomenon that enables the conversion of spin current into charge current, offering promising applications in novel spintronic devices. In conventional ISHE measurements, it is widely recognized that the spin polarization, spin current, and generated charge current are mutually perpendicular. This study systematically investigates the ISHE in Pt/Co/Pt multilayers grown on a single-crystalline yttrium iron garnet (YIG) layer. A non-zero ISHE voltage was obtained along the direction parallel to the external magnetic field within the YIG coercive field range, deviating from the classical ISHE behavior. Our investigation revealed that the in-plane magnetic anisotropy of single-crystalline YIG plays a crucial role, as the easy axis of YIG and the external magnetic field collaboratively determine the polarization direction of the spin current, especially when the external magnetic field is smaller than the YIG coercive force. Furthermore, by tuning the small in-plane magnetization component of the Pt/Co/Pt multilayers, which couples with the YIG magnetization, we were able to control the shape and reversal path of the ISHE voltage loop. These findings deepen our understanding of how magnetic order affects charge current flow in ISHE measurements. The variety of ISHE voltage loop shapes and reversal paths observed suggest potential applications for this device as a magnetic field sensor.

A series of novel single phased Eu³⁺ doped BaZr(PO₄)₂ phosphor were synthesized employing simple solid-state reaction route and studied the influence of different chlorides as fluxes (NH₄Cl, KCl, LiCl and NaCl) on structural and photoluminescence properties. The structural characterization reveals pure phase formation of the as prepared phosphors with monoclinic crystal structure. The photoluminescence (PL) spectra recorded under 392 nm excitation depicts intense emission at 612 nm. Further, the concentration of Eu³⁺ ion was well tuned by carefully studying the PL spectra and the optimised amount of Eu³⁺ ion in BaZr(PO₄)₂ is found to be 3.0 mol%. The luminescence properties of phosphor with added aforementioned fluxes were also studied in detail. NH₄Cl was found to be the best among all the fluxes taken and the photoluminescence intensity of phosphor gets enhanced by 1.43 times of without flux. The Judd-Ofelt theory was employed for determination of spectral parameters from photoluminescent emission spectra. The temperature dependent photoluminescent studies establishes stability of phosphor emission at operating temperatures. The CIE coordinates were evaluated that confirms the pure red emission under n-UV excitation. All the studies indicate the potential of the said phosphor in phosphor converted white light emitting diodes as red emitter and indoor lighting.

Density functional theory is applied to investigate structural, mechanical, electronic, thermoelectric, thermodynamic and optical properties of the inorganic vacancy ordered double perovskite In₂PdCl₆ (IPC). It shows stability in rock-salt structure. It is thermodynamically, dynamically and mechanically stable, elastically anisotropic and ductile with dominant metallic bonding and high melting temperature. It is a semiconductor with direct band-gap of 1.25 eV, which makes it a potential photovoltaic material. It is also a potential thermoelectric material in the temperature regime 600–800 K. Response of different thermodynamic parameters of the IPC to temperature and pressure variation has also been studied. The IPC shows high optical absorption in the almost entire UV region to the violet of the visible spectrum, which is supported by the calculated optical gap of 2.77 eV. Therefore, the IPC may be a potential candidate for optoelectronic and photovoltaic applications in the entire UV to the violet of the visible spectrum.

We fabricated Ba_0.8Sr_0.2TiO${}_3$ (BSTO)/La${}_2$CuO${}_4$ (LCO) heterostructure on SrTiO${}_3$ (STO) substrate and investigated its structure and physical properties. X-ray diffraction and reciprocal space mapping confirm the epitaxial growth of BSTO/LCO/STO heterostructure. X-ray photoelectron spectroscopy and UV–Visible spectroscopy measurements reveal a straddling band alignment of the BSTO/LCO heterojunction. Such band alignment facilitates the accumulation of both electrons and holes at the interface. Their movement depends on the direction of the internal field of the BSTO film. Electrical transport measurements have revealed a signature of insulator-to-metal transition (IMT) in response to applied gate voltages $\pm V_g$. Hall measurements confirm the presence of electron and hole type charge carriers under ＋V${}_g$ and −V${}_g$, respectively. We have proposed a screening mechanism linked to the polarization state of the BSTO film to explain the observed IMT.

There is an increase in demand of the next-generation spintronic devices with stable structural and magnetic properties in varying temperatures. An orthoferrites structure of the Pnma space group has been successfully prepared using high temperature solid-state reaction. In the ${\text{Sm}}_2{\text{Fe}}_2{O}_{5+\delta }$ (SFO) material, $F{e}^{3+}$ ions occupy edge-cantered and face-cantered positions forming the tilted $\text{Fe}{O}_6$ octahedrons with Glazer's notation tilt $a^{-}{a}^{-}{c}^{+}$. The ordering of the rare-earth ions at compensation temperature ($T_{\text{comp}}=2.3K)$, spin-flip transition in the range of $9.4-45.6K$, and a second-type spin-reorientation transition around the anisotropy barrier with lower and higher transitional temperatures, $T_L=465$ and $T_H=480K$ respectively. The canting of spins along with disordered spins at the surface results in a non-zero $T_{\text{comp}}$ and unsaturated magnetization. It is inferred that thermal activation of particle's moment over the anisotropy barriers (known as Kneller's law) only occurs above room temperature.

We report on the dual effects of ion implantation and swift heavy ion on the optical and structural characteristics of polyethylene terephthalate (PET) films using UV–Vis spectrophotometry, FTIR and X-ray diffraction measurements. Samples were first implanted with 150 keV Ag${}^{+}$-ions at different fluences of 1 $\times 10^{16}$, 5 $\times 10^{16}$, and 1 $\times 10^{17}$ ions/cm${}^2$, and thereafter irradiated with 30 MeV Au${}^{7+}$-ions at different fluences, while analysing elemental depth profile in situ on the Time of Flight Heavy Ions Elastic Recoil Detection (ToF-Hi-ERDA) instrument. The elemental depth profile measurements showed considerable atomic depletion of hydrogen from 36% down to below 6% and oxygen from 18% to about 5%. The proportion of carbon increased from 45% to over 87%. The optical bandgap decreased with increasing ion implantation fluence and reduced even further on irradiation with 30 MeV ¹⁹⁷Au${}^{7+}$-ions. The most notable outcome of the implantation was the onset of the precipitation of gold nanoparticles (Au-NPs) in the PET matrix, marked by Localised Surface Plasmon Resonance effects, coincided with a relatively significant drop in the bandgap energy. This latter effect could only be best explained as the result of these Au-NPs in the PET. This suggests that optical bandgap tuning in polymer films, usually achievable through high fluence implantation at low energy (i.e., keV), could also be realized through low fluence irradiation with MeV energy ions. It is surmised that, for the noble metals, NP-induced bandgap modification in PET precludes the need for high fluence to achieve the same. This has the obvious advantage of bandgap alterations at much lower structural damage to the target polymer. As reported by FTIR results, one can observe structural changes with the formation of new chemical bonds on thin films. X-ray diffraction results exhibited one prominent peak corresponding to the (100) plane, which varies in intensity with increased implantation fluence, suggesting a change in the crystallinity of the PET. The decrease in (100) peak or crystallinity was well connected with the presence and decrease of 847, 970, and 1471 cm⁻¹ peaks, which were assigned to the ethylene glycol molecular groups.

This investigation employs first-principles calculations with the Generalized Gradient Approximation (GGA) and modified Becke-Johnson (mBJ) exchange-correlation functionals, employing the Full-Potential Linearized Augmented Plane Wave (FP-LAPW) method. The main objective is to investigate the double perovskites Ba₂SmMoO₆ and Ba₂EuMoO₆. We conduct a thorough analysis of the structural, electrical, magnetic, thermoelectric and optical properties of these materials. Both compounds are stable in ferromagnetic phase, according to structural studies. Ba₂SmMoO₆ has a 3.80 eV energy gap, aligned with the W-X direction, which exhibits half-metallic behavior. On the other hand, Ba₂EuMoO₆ has a 3.03 eV energy gap that is directly aligned with the X-X direction, using mBJ-GGA. Magnetic investigation revealed a total spin magnetic moment of 7 μB for Ba₂EuMoO₆, mainly due to Eu (5.98 μB) and 6 μB for Ba₂SmMoO₆, mainly due to Sm (4.53 μB). It was found that both materials have high Seebeck coefficients and electrical conductivities at high temperatures, with performance improving with temperature. However, the figure of merit (ZT) approaches a value of one, indicating their potential for use in thermoelectric applications at high temperatures. Ba₂SmMoO₆ and Ba₂EuMoO₆ are identified as highly favourable options for effective thermoelectric devices. The high UV absorption, the unique refractive and reflective properties offer potential in photonics, optical coatings, and other fields requiring precise light manipulation.