物理最新文献

Multiferroic nnanoparticles (NPs) of pristine BiFeO₃ (BFO) and Gd-doped BFO, Bi_1 − xGd_xFeO₃ (x = 0.01, 0.03, and 0.05) were synthesized by ethylene glycol-based sol-gel route. The impact of Gd-concentration on their structural, optical, ferroelectric, and magnetic characteristics has been examined. XRD confirmed the phase purity and, it was found that the rhombohedral distorted perovskite structure remained the same on Gd-doping. The average particle size, as determined by FE-SEM, decreased exponentially in the following manner, 46 → 44 → 42 → 41 nm for Gd-doping level varying as 0% → 1% → 3% → 5%, respectively. In Raman spectra of 5%-Gd-doped NPs, the phonon modes corresponding to A₁ ^− 3, A₁ ^− 4 and E peaks show a red shift of 2.6 cm^− 1, 2.5 cm^− 1, and 5.2 cm^− 1, respectively. Well-defined absorption peak at 459 nm was seen in UV-visible absorption spectra of BFO NPs which blue-shifted to 446 nm and the bandgap varied linearly with dopant concentration. 3% Gd-doping was found to be optimum as it caused more than 100% enhancement of the saturation and remanent magnetization, upto 0.702 emu/g and 0.057 emu/g, respectively. In ferroelectric measurements, all samples showed non-saturating P-E hysteresis curves, with pristine BFO having the maximum remnant polarization. These Gd-doped BFO NPs with enhanced magnetic and optical properties are well-suited for applications in photocatalysis and spintronics.

In this study, nanoscale MgO magnetic tunnel junctions (MTJs) with an orthogonal magnetization structure between the free and pinned layers and various junction sizes were fabricated, and their tunnel magnetoresistance (TMR) ratio, resistance-area (RA) product, and low-frequency noise (LFN) behavior were experimentally investigated thoroughly. The circular MTJs with various diameters (80–400 nm) show high TMR ratios of greater than 100% at room temperature (RT) with relatively low RA in the range of 2.8–4.4 Ωµm². We found that the noise power spectral density (PSD) as a function of d.c. bias voltage (V_bias) and perpendicular d.c. bias magnetic field (H_DC) in all junction sizes exhibits 1/f-noise behavior within a wide investigated frequency range from 5 Hz up to 10 kHz. The bias voltage and magnetic field-dependent LFN indicated that the 1/f noise of the MTJs has both electric and magnetic origins. The results show that though the TMR ratio and RA product are size-independent, the Hooge parameter for the parallel (P) state (α_P) is strongly dependent on the MTJ size, and its values decrease with decreasing MTJ size, suggesting the reduction of electronic 1/f noise as the MTJ size shrinks. This is the first experimental report on the size dependency of electronic 1/f noise in nano-sized MTJs. The results may open a new approach for reducing not only magnetic but also electronic 1/f noises in MTJs by downscaling, thereby increasing the sensitivity of MTJ nanosensors.

The recent observation of global spin polarization of (Lambda ) ((bar{Lambda })) hyperons and the spin alignment of (phi ) and (K^{*0}) vector mesons create remarkable interest in investigating the particle polarization in the relativistic fluid produced in heavy-ion collisions at GeV/TeV energies. Among other sources of spin polarization phenomena, the Debye mass of a medium plays a crucial role in particle polarization. Any modification brought to the effective mass due to the temperature, strong magnetic field (eB), baryonic chemical potential ((mu _{B})), medium anisotropy ((xi )), and vorticity, etc., certainly affects the particle spin polarization. In this work, we explore the global hyperon spin polarization and the spin alignment of vector mesons corresponding to the strong magnetic field, baryonic chemical potential, and medium anisotropy. We find that the degree of spin polarization is flavor-dependent for hyperons. Meanwhile, vector meson spin alignment depends on the hadronization mechanisms of initially polarized quarks and anti-quarks. Medium anisotropy significantly changes the degree of spin polarization compared to the magnetic field and baryon chemical potential.

We analyze the dynamics of the Friedmann–Lemaître universes taking into account the different roles played by the fluid parameter and the cosmological constant, as well as the degenerate character of the equations. We find that the Friedmann–Lemaître system reduces to four qualitatively inequivalent normal forms and write down the sets of all stable perturbations that may result (the ‘versal unfoldings’). These sets are of small codimension up to three. We then describe all possible parameter-dependent solutions and their transfigurations to other forms during evolution through the bifurcation sets, these are also fully described. This analysis leads to a picture of cosmological evolution determined by new parameters related to codimension which are zero in standard cosmology. The emerging versal solutions are all free of singularities, while other properties of them are also discussed.

We discuss the fine-tunings of nuclear reactions in the Big Bang and in stars and draw some conclusions on the emergence of the light elements and the life-relevant elements carbon and oxygen. We also stress how to improve these calculations in the future. This requires a concerted effort of different communities, especially in nuclear reaction theory, lattice QCD for few-nucleon systems, stellar evolution calculations, particle physics and philosophy.

This research investigates the propagation of Rayleigh waves in an orthotropic medium containing voids, employing nonlocal elasticity and the three-phase lag (TPL) model. The presence of voids, nonlocal effects, and diffusion are critical factors that significantly influence the behavior of Rayleigh waves, which are crucial for various engineering applications and geophysical explorations. The orthotropic medium’s directional dependence on mechanical properties, combined with voids, adds complexity to the wave propagation dynamics. We utilize the TPL model to incorporate phase lags in heat conduction, mechanical deformation, and mass diffusion, providing a comprehensive framework for analyzing these interactions. Normal mode analysis is employed to derive the dispersion relations and study the effects of nonlocal elasticity on wave characteristics. The inclusion of nonlocal elasticity accounts for long-range interactions, enhancing the accuracy of the model in predicting wave behavior. Our findings reveal that the presence of voids, nonlocal elasticity, and diffusion significantly impact the propagation speed, attenuation coefficient, penetration depth, and specific loss of Rayleigh waves. The TPL model effectively captures the combined effects of these factors, showing that nonlocal elasticity introduces additional complexity and dispersion in wave propagation. Diffusion tends to smooth out the wave characteristics, while the presence of voids influences the propagation speed, attenuation coefficient, penetration depth, and specific loss. This study contributes to the development of more accurate predictive models for wave propagation in complex media, with implications for materials science, structural engineering, and geophysical exploration. The results highlight the necessity of considering voids, nonlocal elasticity, and diffusion when analyzing Rayleigh wave propagation in orthotropic media.