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Register a new userDesigning multi-level resistance states for multi-bit storage using half doped manganites
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Designing nonvolatile multi-level resistive devices is the necessity of time to go beyond traditional one-bit storage systems, thus enhancing the storage density. Here, we explore the electronic phase competition scenario to design multi-level resistance states using a half doped CE-type charge ordered insulating bulk manganite, $Sm_{0.5}Ca_{0.25}Sr_{0.25}MnO_3$ (SCSMO). By introducing electronic phase coexistence in a controllable manner in SCSMO, we show that the system can be stabilized into several metastable states, against thermal cycling, up to 62 K. As a result the magnetization (and the resistivity) remains unaltered during the thermal cycling. Monte Carlo calculations using two-band double exchange model, including super-exchange, electron-phonon coupling, and quenched disorder, show that the system freezes into a phase coexistence metastable state during the thermal cycling due to the chemical disorder in SCSMO. Using the obtained insights we outline a pathway by utilizing four reversible metastable resistance states to design a prototype multi-bit memory device.
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Recently, based on the refined crystal structure of Pr0.6Ca0.4MnO3 from neutron diffraction, Daoud-Aladine et al.[PRL89,97205(2002)] have proposed a new ground state structure for the half-doped manganites R0.5Ca0.5MnO3, where R is a trivalent ion like Bi,La,Pr,Sm or Y. Their proposal describes the CE magnetic structure attributed to these materials as an arrangement of dimers along the ferromagnetic Mn zig-zag chains that form it. However, the dimers proposal is in conflict with the Goodenough-Kanamori-Anderson rules, which give a coherent description of many transition metal insulating compounds and predict the coexistence of Mn3+ and Mn4+ ions in equal parts in the half-doped manganites. On the other hand, Rivadulla et al.[PRB 66, 174432 (2002)] have studied several single crystal samples of half-doped manganites and propose a phase diagram in terms of the tolerance factor which contains both types of structures. In the present work we have calculated the magnon dispersion relations for the CE magnetic structure, arising for each type of proposal: the charge ordered and the dimer phases, respectively. We consider a three-dimensional unit cell containing 16 spins, and compare the magnetic excitations along different paths in the first Brillouin zone. We conclude that measurement of the magnon dispersion relations should allow a clear distinction between the two proposals, predicting qualitative differences arising along specific directions of propagation in the first Brillouin zone.
Thermal comfort of textiles plays an indispensable role in the process of human civilization. Advanced textile for personal thermal management shapes body microclimates by merely regulating heat transfer between the skin and local ambient without wasting excess energy. Therefore, numerous efforts have recently been devoted to the development of advanced thermoregulatory textiles. In this review, we provide a unified perspective on those state-of-the-art efforts by emphasizing the design of diverse heat transfer pathways. We focus on engineering certain physical quantities to tailor the heat transfer pathways, such as thermal emittance/absorptance, reflectance and transmittance in near-infrared and mid-infrared radiation, as well as thermal conductance in conduction. Tuning those heat transfer pathways can achieve different functionalities for personal thermal management, such as passive cooling, warming, or even dual-mode (cooling-warming), either static switching or dynamic adapting. Finally, we point out the challenges and opportunities in this emerging field, including but not limited to the impact of evaporation and convection with missing blocks of heat pathways, the bio-inspired and artificial-intelligence-guided design of advanced functional textiles.
Reconfigurable photonic systems featuring minimal power consumption are crucial for integrated optical devices in real-world technology. Current active devices available in foundries, however, use volatile methods to modulate light, requiring a constant supply of power and significant form factors. Essential aspects to overcoming these issues are the development of nonvolatile optical reconfiguration techniques which are compatible with on-chip integration with different photonic platforms and do not disrupt their optical performances. In this paper, a solution is demonstrated using an optoelectronic framework for nonvolatile tunable photonics that employs undoped-graphene microheaters to thermally and reversibly switch the optical phase-change material Ge$_2$Sb$_2$Se$_4$Te$_1$ (GSST). An in-situ Raman spectroscopy method is utilized to demonstrate, in real-time, reversible switching between four different levels of crystallinity. Moreover, a 3D computational model is developed to precisely interpret the switching characteristics, and to quantify the impact of current saturation on power dissipation, thermal diffusion, and switching speed. This model is used to inform the design of nonvolatile active photonic devices; namely, broadband Si$_3$N$_4$ integrated photonic circuits with small form-factor modulators and reconfigurable metasurfaces displaying 2$pi$ phase coverage through neural-network-designed GSST meta-atoms. This framework will enable scalable, low-loss nonvolatile applications across a diverse range of photonics platforms.
We present a piezoelectric-driven uniaxial pressure cell that is optimized for muon spin relaxation and neutron scattering experiments, and that is operable over a wide temperature range including cryogenic temperatures. To accommodate the large samples required for these measurement techniques, the cell is designed to generate forces up to 1000 N, and to minimize the background signal the space around the sample is kept as open as possible. We demonstrate here that by mounting plate-like samples with epoxy, a uniaxial stress exceeding 1 GPa can be achieved in an active volume of 5 mm3. We show that for practical operation it is important to monitor both the force and displacement applied to the sample. Also, because time is critical during facility experiments, samples are mounted in detachable holders that can be rapidly exchanged. The piezoelectric actuators are likewise contained in an exchangeable cartridge.
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