We have done the fabrication of NiFe₂O₄ nanoparticle at room temperature under the variation of magnetic field. Here, we have measured current-voltage (I-V) characteristics and the impedance spectroscopy of our device. From our experiment, it has been found that our sample shows magnetoresistance with positive value and magnetic field dependent electrical hysteresis. I-V curve reveals the existence of electrical memory effect in our sample. The memory window of our sample is found to inversely proportional to the applied magnetic field thus, electrical hysteresis of our sample has been found to vary under the application of the magnetic field. In our work we have shown the magnetic field dependent electrical hysteresis and impedance spectroscopy of our sample.

Keywords: Nano particle, Hysteresis, Magnetic field, Impedance spectroscopy

Perovskite appears to be the most promising candidate for thin-film optoelectronic devices due to its excellent optoelectronic properties, low-cost fabrication, and high photovoltaic performance. However, tin-based perovskite devices possess a few issues related to thermal instability and poor performance. A study on thermal instability will be important to understand the inner mechanism of the device. To find out the cause of thermal instability, a study on the temperature coefficient of different electrical parameters is necessary. In this work, the effect of temperature on electrical parameters of methylammonium tin iodide (CH₃NH₃SnI₃) and methylammonium tin chloride (CH₃NH₃SnCl₃) based Schottky devices having an ITO/Perovskites/Al architecture has been studied using a SCAPS-1D simulator. The coefficients of the temperature of these parameters have been calculated. The currentvoltage analysis shows the positive temperature coefficient of barrier height and negative temperature coefficient of the ideality factor. The estimated values of the absolute temperature coefficient of barrier height and ideality factor are 1.28 meV per K and 0.07 per K for CH₃NH₃SnI₃ and 1.14 meV per K and 0.02 per K for CH₃NH₃SnCl₃ perovskite-based Schottky device, respectively. The comparative study shows that the CH₃NH₃SnCl₃ perovskite has better thermal stability. We have also studied the variation of thickness, defect densities, and acceptor concentration of the perovskites, and finally, an optimized device of both types of Schottky devices has been proposed. This study reveals the temperature sensitiveness of lead-free tin-based perovskite-based Schottky devices. The decrease in the value of different device parameters will be very informative for further study to get temperature invariant performances of lead-free perovskite solar cells.

Keywords: Lead-free Perovskites, Schottky device, SCAPS-1D, Electrical parameters, Temperature coefficients, Photovoltaic parameters.

We have performed a systematical calculation for Cr and Dy co-doped ZnO by the first principles method using Quantum-Espresso. A lot of interesting results were found from the analysis of energy band structures and density of states. From spin-polarized calculations within the framework of density functional theory, we have noticed that the value of total magnetization of co-doped ZnO is substantially enhanced compared to that of pure ZnO, and total magnetic moments mainly come from the contribution of Cr 3d and Dy 4f states. Our findings indicate that Cr and Dy co-doped ZnO are capable magneto-electronic materials and they can be used for nanoscale spintronics device material.

The existence of two inequivalent valleys in the Brillouin zone of some two-dimensional crystals with honeycomb lattice structure provides electrons to possess an extra degree of freedom, known as pseudospin/valley in addition to their intrinsic charge and spin. A dice lattice, in which the low energy excitations are described by the Dirac-Weyl Hamiltonian with pseudospin 𝑆 = 1, also has the valley degree of freedom. Here, we consider an inversion-symmetry broken low energy model of a symmetrically biased dice lattice. We find that the Berry curvature has equal magnitude with opposite signs in two valleys. This causes the electrons to acquire opposite anomalous velocities in the respective valleys. The Hall conductivity is calculated using the semi-classical formulation of electron dynamics. The dependence of the valley contrasted Hall conductivity on the chemical potential at various temperatures is shown

Keywords: Dirac- Weyl Hamiltonian, Berry curvature, Hall conductivity, semi-classical formulation.

We have investigated a cosmological model of matter-dominated universe with a specified form of dynamic cosmological Λ-term, varying as Λ = 𝑙𝐻̇ + (𝑙 + 𝜆)𝐻²+1/2𝜂𝜌, where 𝑙, 𝜆 and 𝜂 are constants. We study the aforesaid cosmological model as an explanation for the accelerated expansion of the universe and obtain constraints on various model parameters for the estimation of the present values of cosmological parameters e.g. deceleration parameter, equation of state parameter, age of the universe. We also investigate the statefinder parameter {𝑟, 𝑠}. In order to investigate stability of the system, we have treated the system in terms of dynamical system theory and studied dynamical properties and investigated critical points. By performing corresponding critical points analysis we have investigated different eras in the course of evolution of the universe.

Keywords:FLRW Universe, Dynamical cosmological constant, Observational parameters, Phase space analysis