First page: 121101 Abstract: We report on the dielectric and electrocaloric properties of Ba1−yCayTi1−xHfxO3 for compositions 0.12 < x < 0.18 and y = 0.06, as well as x = 0.15 and 0 < y < 0.15, synthesized by the conventional solid-state reaction method. The addition of Hf/Ca broadens the ferroelectric-paraelectric phase transition while moving it toward room temperature. Two interferroelectric transitions are seen to converge, together with the ferroelectric–paraelectric phase transition, at ∼335 K for 0.12 < xc < 0.135 and y = 0.06. Consistent with the dielectric properties, the electrocaloric effect maximizes closer to room temperature with increasing Hf/Ca substitutions, which promote larger temperature spans. The electrocaloric responsivity gradually decreases from 0.2 to 0.1 K mm kV−1 with the addition of Hf/Ca. A homemade quasi-adiabatic calorimeter is employed to measure “directly” the electrocaloric data, which are also calculated from polarization-versus-electric-field cycles using “indirect” standard procedures. The comparison between measured and calculated values highlights the importance of having access to direct methods for a reliable determination of the electrocaloric effect. PubDate: Mon, 04 Dec 2023 00:00:00 GMT DOI: 10.1063/5.0173585 Issue No:Vol. 11, No. 12 (2023)
First page: 121102 Abstract: MAX phases are a class of intrinsically nanolaminated materials, which combine features of metals and ceramics, owing to the alternating metallic and covalent bonding between atomic layers. Magnetic MAX phases have been known for a decade, but ferromagnetism at room temperature in this highly anisotropic system has been elusive, limiting their value as magnets in practice. Here, we show that a MAX phase with a strong ferromagnetic response is obtained by substituting Mn with Cr on the M-site in the well-known Mn2GaC. The ferromagnetic response is observed in (Mn1−xCrx)2GaC with 0.06 < x < 0.29 up to temperatures well exceeding room temperature (489 K). The strongest magnetization is achieved with x = 0.12, reaching a saturation moment of 1.25 μB and a remanence of 0.67 μB per M-atom at 3 K and maintaining 0.90 and 0.44 μB per M-atom, respectively, at 300 K. This is the first experimental report of a significant ferromagnetic response in a MAX phase at room temperature. The results open the door to the use of MAX phases in a broad range of applications, from bulk magnets in power electronics to spintronic devices. PubDate: Mon, 04 Dec 2023 00:00:00 GMT DOI: 10.1063/5.0176571 Issue No:Vol. 11, No. 12 (2023)
First page: 121103 Abstract: Manipulating elastic waves using a transformation approach is challenging due to the complex constitutive relationship. However, for flexural waves, approximated as scalar waves, two straightforward approaches emerge based on geometric curvature and plate thickness. Here, we develop transformation theory to establish equivalence between curved plates of different shapes and thickness profiles. Introducing tailor-made thickness profiles on a given curved shape enables illusion effects, where flexural waves propagate as if on a flat plate or on another curved plate with a totally different configuration. Numerical simulations and experimental field mapping confirm the effectiveness of these illusions. Our approach to flexural wave illusion finds applications in structural designs with material and shape constraints and holds the potential for absorption or vibration control, wavefront shaping, chaotic dynamics, and topology control. PubDate: Mon, 04 Dec 2023 00:00:00 GMT DOI: 10.1063/5.0174078 Issue No:Vol. 11, No. 12 (2023)
First page: 121104 Abstract: Parity-time (PT) symmetric coupled resonator systems have exhibited intriguing and unexpected properties in optics and electronics. Here, we extend it to acoustics and report a coupled Mie resonators (MRs) system respecting PT symmetry. The system is constructed with two parallel waveguides connected by an aperture and two MRs placed symmetrically at both sides of the aperture. Instead of using active elements or complex refractive index modulation without gain, we exploit the incident waves of the waveguide as an effective gain so that PT symmetry with balanced loss and gain is realized by only passive materials. Coherent perfect absorption (CPA), which can completely absorb the in-phase excitations with the same intensity provided from two opposite directions, is observed in the PT symmetric phase and at the exceptional point but not in the broken phase. In addition, by varying the relative phase between the two incident waves, the coherent absorption can be tuned from CPA to zero. Our design may provide a flexible platform to research PT symmetry in acoustics and may have applications in tunable noise control, acoustic modulators, and switches. PubDate: Mon, 04 Dec 2023 00:00:00 GMT DOI: 10.1063/5.0179484 Issue No:Vol. 11, No. 12 (2023)
First page: 121105 Abstract: An ex situ chemical etching method was developed to achieve a SnO2-terminated surface in BaSnO3 films. An SnO2-terminated surface is crucial for the formation of a (LaO)+/(SnO2)0 interface structure to form the two-dimensional electron gas (2DEG) state at the LaInO3 (LIO)/BaSnO3 (BSO) interface. By employing a 9:1 mixture of acetone and water, the etching rate of the surface barium oxide (BaO) layer could be effectively controlled, taking advantage of the solubility of BaO in water. To determine the optimal etching conditions, we investigated the relationship between the etching time and the resulting 2DEG conductance. The optimum times for maximizing the conductance of the 2DEG state were found to be 90 s on SrTiO3 substrates and 40 s on MgO substrates, generating a higher conductance than the in situ SnO2 dusting method reported earlier. The surface properties before and after the chemical etching were analyzed by angle reserved x-ray photoelectron spectroscopy. PubDate: Mon, 04 Dec 2023 00:00:00 GMT DOI: 10.1063/5.0173833 Issue No:Vol. 11, No. 12 (2023)
First page: 121106 Abstract: We investigated the influence of the buffer material and a cryogenic temperature deposition process on the voltage-controlled magnetic anisotropy (VCMA) effect for an ultrathin CoFeB layer in bottom-free type MgO-based magnetic tunnel junctions prepared by a mass production sputtering process. We used Ta and TaB buffers and compared the differences between them. The TaB buffer enabled us to form a flat and less-contaminated CoFeB/MgO interface by suppressing the diffusion of Ta with maintaining a stable amorphous phase. Furthermore, the introduction of cryogenic temperature deposition for the ultrathin CoFeB layer on the TaB buffer improved the efficiency of the VCMA effect and its annealing tolerance. Combining this with interface engineering employing an Ir layer for doping and a CoFe termination layer, a large VCMA coefficient of −138 ± 3 fJ/Vm was achieved. The developed techniques for the growth of ultrathin ferromagnet and oxide thin films using cryogenic temperature deposition will contribute to the development of high-performance spintronic devices, such as voltage-controlled magnetoresistive random access memories. PubDate: Mon, 04 Dec 2023 00:00:00 GMT DOI: 10.1063/5.0176263 Issue No:Vol. 11, No. 12 (2023)
First page: 121107 Abstract: The Li-ion conductivities of Li3InCl6 (LIC), which is a promising chloride solid electrolyte, and its compositional derivatives, Nb5+- and Zr4+-doped LIC, i.e., Li3−2xIn1−xNbxCl6 and Li3−yIn1−yZryCl6, respectively, were experimentally and computationally investigated. An increase in the ionic conductivity caused by Nb5+ or Zr4+ doping, which was due to the increase in Li vacancies, was observed in both the experimental and computational results. Nb5+ doping yielded a larger increase in conductivity at 60 °C. First-principles molecular dynamics studies indicated two factors affecting the Li-ion conductivity under doping with higher-valent ions: (1) the vacancy trapping effect and (2) the reduction in the phase-transition temperature from a Li/vacancy ordered structure to a disordered structure. In particular, in factor (2), the effect of Nb5+ doping is larger than that of Zr4+ doping, which supports the improvement in ionic conductivity at 333 K in the experiment. PubDate: Mon, 04 Dec 2023 00:00:00 GMT DOI: 10.1063/5.0167817 Issue No:Vol. 11, No. 12 (2023)
First page: 121108 Abstract: Two-dimensional electron gases (2DEGs) based on KTaO3 are emerging as a promising platform for spin-orbitronics due to their high Rashba spin–orbit coupling (SOC) and gate-voltage tunability. The recent discovery of a superconducting state in KTaO3 2DEGs now expands their potential towards topological superconductivity. Although the band structure of KTaO3 surfaces of various crystallographic orientations has already been mapped using angle-resolved photoemission spectroscopy (ARPES), this is not the case for superconducting KTaO3 2DEGs. Here, we reveal the electronic structure of superconducting 2DEGs based on KTaO3 (111) single crystals through ARPES measurements. We fit the data with a tight-binding model and compute the associated spin textures to bring insight into the SOC-driven physics of this fascinating system. PubDate: Thu, 07 Dec 2023 00:00:00 GMT DOI: 10.1063/5.0169750 Issue No:Vol. 11, No. 12 (2023)
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