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Gadolinium stand as the favored choice among magnetic refrigerant materials for numerous active magnetic regenerator (AMR) prototypes due to its remarkable ability to exhibit a substantial change in magnetic entropy. This unique characteristic arises from its status as one of the elemental ferromagnets with a high Curie temperature, closely aligning with room temperature conditions, and undergoing a second-order magnetic phase transition. In this comprehensive study, we employ density functional theory (DFT) calculations to explore the structural, electronic, and magnetic properties of both Gadolinium bulk and film configurations. Our primary objective is to gain a deeper understanding of the intricate physics underlying the intriguing magnetocaloric features observed in Gadolinium. This investigation provides valuable insights into the potential applications and the broader implications of Gadolinium in the realm of magnetic refrigeration technology.

Silicene, a new two-dimensional (2D) material has attracted intense research because of the ubiquitous use of silicon in modern technology. However, producing free-standing silicene has proved to be a huge challenge. Until now, silicene could be synthesized only on metal surfaces where it naturally forms strong interactions with the metal substrate that modify its electronic properties. Here, we report the first experimental evidence of silicene sheet on an insulating NaCl thin film. This work represents a major breakthrough; for the study of the intrinsic properties of silicene, and by extension to other 2D materials that have so far only been grown on metal surfaces.

Combining multiple degrees of freedom in strongly-correlated materials such as transition-metal oxides would lead to fascinating magnetic and magnetocaloric features. Herein, the strain effects are used to markedly tailor the magnetic and magnetocaloric properties of PrVO3 thin films. The selection of appropriate thickness and substrate enables us to dramatically decrease the coercive magnetic field from 2.4 T previously observed in sintered PVO3 bulk to 0.05 T for compressive thin films making from the PrVO3 compound a nearly soft magnet. This is associated with a marked enhancement of the magnetic moment and the magnetocaloric effect that reach unusual maximum values of roughly 4.86 uB and 56.8 J/kg K in the magnetic field change of 6 T applied in the sample plane at the cryogenic temperature range (3 K), respectively. This work strongly suggests that taking advantage of different degrees of freedom and the exploitation of multiple instabilities in a nanoscale regime is a promising strategy for unveiling unexpected phases accompanied by a large magnetocaloric effect in oxides., Comment: This paper is accepted for publication in Applied Physics Letters

High critical temperature cuprate superconducting materials are composed of copper oxide layers and interlayer charge reservoirs. When not doped, these cuprates are antiferromagnetic insulators. We propose to design new materials by combining alternating layers of parents of hole-doped and electron-doped of these cuprates and modifications thereof. Our goal is to find undoped cuprates that can be either an antiferromagnetic insulator or a quantum metal. The term quantum metal means a metal characterized by long range antiferromagnetic order or only strong antiferromagnetic correlations, i.e., it is thus a stable ground state against any other perturbations. The new metallic states sought here could be precursors to new superconducting states in the absence or presence of doping. Using the density functional theory, we report on two compounds {La}{Pr}CuO4 and {La}{V}CuO4 that illustrate the different physics described above. The curly brackets mean that the preparation of these compounds shall be done by depositing a layer containing Pr, then one CuO2 layer, then finally the La layer in {La}{Pr}CuO4 for example. The configuration formed by the positions of the charge reservoir atoms with respect to the CuO2 layer is an important factor in the new procedure we propose here. This paper reports on the X-ray diffraction, electronic, optical, and magnetic properties of these hypothetical materials. We found that {La}{Pr}CuO4 is a Mott insulator, but {La}{V}CuO4 is an undoped correlated quantum metal with long-range order. Our calculations were performed using the linearized plane wave method (FP-LAPW) implemented within the Wien2k software., Comment: 27 pages, 19 figures

The effect of the orientation of the cation MA (i.e., CH3NH3) on the physical properties of MAPbI3 are investigated using the density functional theory. We report that the Fermi energy level exhibits a large variation with MA orientation, and it is this Fermi level variation that makes this material unique and so different from the non-organic perovskites. The Fermi level variation with orientation of MA is proposed to be responsible for the experimentally observed intrinsic open-circuit voltage V_OC, ambipolarity, and long lifetime of the excitons. Based on our results, ferroelectric domains in the low-temperature orthorhombic phase or clusters of MA molecules not rotating in unison (as a consequence of e.g. impurities and/or defects) in the higher-temperature tetragonal and cubic phases are proposed to be responsible for ambipolarity. This is because any given two adjacent domains or clusters with different MA s average orientations may have very different Fermi levels, causing them to behave as an effective diode. Also, the measured significant lifetime of excitons in MAPbI3 finds a natural explanation using this effective diode. Thus, our work provides a unified manner for explaining at least these three important properties in terms of the rotation-induced Fermi level variations. We used the density functional theory to get our results., Comment: 30 pages, 11 figures

In this work, a successful synthesis of magnetic cobalt ferrite (CoFe2O4) nanoparticles is presented. The synthesized CoFe2O4 nanoparticles have a spherical shape and highly monodisperse in the selected solvent. The effect of different reaction conditions such as temperature, reaction time and varying capping agents on the phase and morphology is studied. Scanning transmission electron microscopy showed that the size of these nanoparticles can be controlled by varying reaction conditions. Both X-ray diffraction and energy dispersive X-ray spectroscopy corroborate the formation of CoFe2O4 spinel structure with cubic symmetry. Due to optimized reaction parameters, each nanoparticle was shown to be a single magnetic domain with diameter ranges from 6 to 16 nm. Finally, the magnetic investigations showed that the obtained nanoparticles are superparamagnetic with a small coercivity value of about 315 Oe and a saturation magnetization of 58 emu/g at room temperature. These results make the cobalt ferrite nanoparticles promising for advanced magnetic nanodevices and biomagnetic applications., Comment: 10 pages, 9 figures

We study the magnetic properties of a mixed Ising ferrimagnetic system, in which the two interacting sublattices have spins $\sigma$, $(\pm 1/2)$ and spins $S$, $(\pm 3/2,\pm 1/2)$ in the presence of a random crystal field, with the mean field approach. The obtained results show the existence of some interesting phenomena, such as the appearance of a new ferrimagnetic phase namely the partly ferrimagnetic phase $(m_{\sigma}=\frac{-1}{2},m_S=+1)$ and consequently the existence of three topologically different types of phase diagrams. The effect of increasing the exchange interaction parameter $J$, at very low temperature is investigated. The transitions shown in these phase diagrams are in good agreement with those obtained in the ground state case.