SPIN

We have proposed a mean field theoretical model in the coexistence of superconductivity and Jahn–Teller (JT) effect for the study of specific heat in iron-based superconductors in the presence of an external magnetic field. The superconducting (SC) gap and lattice strain energy expressions are calculated using Zubarev’s technique of double-time electron Green’s function and solved numerically. The specific heat jump at the critical temperatures are observed. Keeping fixed the SC transition temperature at 28K for the iron pnictide $LaOFeAs$ like superconductors, the coefficient of electronic specific heat $\gamma$ at low temperatures is determined to be 5.75mJ/molK² in the pure SC state and 4.76mJ/molK² in the coexistence state of SC and JT effect which are in agreement with some experimental results. The effect of the external magnetic field on the specific heat is studied.

Inductively coupled plasma (ICP) has been widely used in semiconductor manufacturing, especially in nanoscale etching and deposition process. It is important to understand the relationship among the 13.56MHz rf-biased power and the etching process. In this study, the effect of dual rf power on the SiO₂ sputter etching is investigated by measuring the ion energy distributions (IEDs), ion flux and sputter etching rate. The results show that the IEDs transforms from uni-modal towards bi-modal distribution when rf-biased power is applied to electrode. The influence of source power, bias power, discharge pressure and current ratio on the ion flux, IEDs are investigated in detail. The energy separations measured by RFEA are in good agreement with analytical model. The ion flux can be modulated by the 13.56MHz rf-biased power. Moreover, the coil current ratio expands the control window of the ion bombardment energy for the ICP etch equipment while. Finally, an ion-enhanced etching model is introduced to obtain the sputter etching rate and reveals the influence of discharge conditions on the etch rate.

Magnetic and electronic properties of LiVOPO₄ and VOPO₄ cathodes have been studied using ab initio calculations, high temperature series expansions (HTSEs) calculations and Monte Carlo simulations (MCSs). Self-consistent ab initio calculations, based on Density Functional Theory approach (DFT) and using Full Potential Linear Augmented Plane Wave (FLAPW) method, were performed to investigate both electronic and magnetic properties of the LiVOPO₄. Polarized spin and spin–orbit coupling are included in calculations within the framework of the antiferromagnetic state between two adjacent V plans. Magnetic moments considered to lie along (010) axes are computed. Average equilibrium voltage over a full cycle ($V_{\mathrm{\text{cell}}}$) of the LiVOPO₄, battery have been estimated. Computed magnetic moments are used as input for HTSEs to compute other magnetic parameters using the mean field theory, MCSs and HTSEs. The obtained results by HTSEs and MCSs are comparable with experiments results.

We have studied the influence of underlayer thickness on the static and dynamic magnetic properties in perpendicular exchange-biased (PEB) [Pd/CoFeB]₄/MnIr multilayers for both Pd and Cu cases. The PEB field $H_{\mathrm{\text{eb}}}$ decreases and the coercivity field $H_c$ increases with increasing thickness of Cu and Pd underlayers. The dynamic results demonstrate that the Gilbert damping constant $\alpha$ increases with increasing the underlayer thickness in both cases. We attribute the enhancement in $\alpha$ to the increased interfacial spin disordering due to the higher roughness. The increasing of spin disordering in the dead layer enhances the interfacial spin scattering or spin dephasing which makes an additional contribution to the damping constant $\alpha$. In addition, we find that the intrinsic damping constant becomes larger when exchange bias effect is established, because the introduction of anti-ferromagnetic (AFM) layer adds another transfer channel of angular momentum of ferromagnetic (FM) layer.

The magnetic properties of the metal/semiconductor structure can be modulated by the semiconductor layer thickness and therefore in the present paper, a series of trilayers of ion beam sputtered Cobalt–Silicon–Cobalt (Co/Si/Co) were grown to study the interface characteristics and their connections with magnetic properties. The thickness of Co layer, $t_{\mathrm{\text{Co}}}$, is fixed to 3nm, while varying the thickness of Si sandwich layer, $t_{\mathrm{\text{Si}}}$, from 1.5nm to 4nm, respectively. Grazing incidence X-ray diffraction (GIXRD), grazing incidence X-ray reflectivity (GIXRR), Atomic Force Microscopy (AFM) and Magneto-Optic Kerr Effect (MOKE) techniques were employed to study the crystal structure, surface and interface structure, morphology and magnetic characteristics of thin films. X-ray reflectivity measurements show substantial intermixing between the layers leading to trilayers of complicated structure at the interface during deposition. At $t_{\mathrm{\text{Si}}}=1.5$nm, whole Si layer is converted into silicide, whereas at higher spacer layer thickness ($t_{\mathrm{\text{Si}}}$), in addition to silicide layer, an unreacted elemental layer of Si also remains in the spacer. A magneto-optical measurement reveals the presence of anti-ferromagnetic coupling in these samples and the strength of coupling between Co layers is found to be depended on $t_{\mathrm{\text{Si}}}$.

We present a theoretical model study of superconductivity for iron-based high-$T_c$ superconductors in s${}^{\pm }$-wave symmetry, considering two degenerate orbitals and the electron hopping up to the third nearest neighbor as a two-orbital model. The analytic expression for the temperature dependence of the superconducting order parameter is derived by Zubarev’s technique of double time single particle Green’s function method and solved self-consistently. The effect of inter orbital hopping on the superconducting energy gap parameter and electronic specific heat is studied.

We present a mean-field theoretical model study for the coexistence of the two strongly interacting charge density wave (CDW) and spin density wave (SDW) for iron-based superconductors in the under-doped region before the onset of the superconductivity in the system. The analytic expressions for the temperature dependence of the CDW and SDW order parameters are derived by using Zubarev’s technique of double-time single particle Green’s functions and solved self-consistently. Their interplay is studied by varying both the CDW and SDW coupling constants. Further, the electronic density of states (DOS) for the conduction electrons are studied in the pure CDW and SDW states and coexistence state for the cases, where the CDW transition temperature is greater than the SDW transition temperature and vice versa, which show two gap parameters.

Using density-functional theory within the generalized-gradient approximation, we explore the magnetic behavior induced by nonmagnetic atoms Ra and Bi in RaBi binary compound in five crystalline structures (rocksalt (B1), CsCl (B2), ZB (B3), WZ (B4) and NiAs (B8${}_1))$. In all the structures considered, the ferromagnetic (FM) phase is energetically less favorable compared to the paramagnetic phase except in the ZB and WZ structures. In the (FM) ZB and WZ structures, we obtained that the spin polarized 6$p$ orbitals of bismuth in the RaBi compound results in a half-metallic (HM-FM) ferromagnet with an integer magnetic moment of 1${\mu }_{\mathrm{\text{B}}}$ per formula unit. We calculated spin flip gaps (half-metallic gaps) of 0.16 and 0.18eV within GGA-PBE approach, 0.40eV and 0.33eV with mBJ-GGA-PBE approach for ZB and WZ structures, respectively. The RaBi compound in ZB and WZ structures would have potential application in spintronic devices.