Magnetic order in most materials occurs when magnetic ions with finite moments arrange in a particular pattern below the ordering temperature. Intriguingly, if the crystal electric field (CEF) effect results in a spin-singlet ground state, a magnetic order can still occur due to the exchange interactions between neighboring ions admixing the excited CEF levels. The magnetic excitations in such a state are spin excitons generally dispersionless in reciprocal space. Here we use neutron scattering to study stoichiometric Ni2Mo3O8, where Ni2+ ions form a bipartite honeycomb lattice comprised of two triangular lattices, with ions subject to the tetrahedral and octahedral crystalline environment, respectively. We find that in both types of ions, the CEF excitations have nonmagnetic singlet ground states, yet the material has magnetic order. Furthermore, CEF spin excitons from the tetrahedral sites form a dispersive diffusive pattern around the Brillouin zone boundary, likely due to spin entanglement and geometric frustrations.
Magnetic order in most materials occurs when magnetic ions with finite moments arrange in a particular pattern below the ordering temperature. Intriguingly, if the crystal electric field (CEF) effect results in a spin-singlet ground state, a magnetic order can still occur due to the exchange interactions between neighboring ions admixing the excited CEF levels. The magnetic excitations in such a state are spin excitons generally dispersionless in reciprocal space. Here we use neutron scattering to study stoichiometric Ni2Mo3O8, where Ni2+ ions form a bipartite honeycomb lattice comprised of two triangular lattices, with ions subject to the tetrahedral and octahedral crystalline environment, respectively. We find that in both types of ions, the CEF excitations have nonmagnetic singlet ground states, yet the material has magnetic order. Furthermore, CEF spin excitons from the tetrahedral sites form a dispersive diffusive pattern around the Brillouin zone boundary, likely due to spin entanglement and geometric frustrations.
“…Similarly one can also rationalize in this way the superstructures obtained in other systems, e.g. in Zn 2 Mo 3 O 8 , which is a prototype of a large and very rich class of materials based on Mo 3 O 8 clusters, in which such phenomena as giant optical diode effect [87], valence-bond condensation and freezing of part of magnetic moments [88][89][90][91], multiferroicity [92][93][94][95] etc. were observed.…”
The properties of transition metal compounds are largely determined by nontrivial interplay of different degrees of freedom: charge, spin, lattice, but also orbital ones. Especially rich and interesting effects occur in systems with orbital degeneracy. They result in the famous Jahn-Teller effect leading to a plethora of consequences, in static and in dynamic properties, including nontrivial quantum effects. In the present review we discuss the main phenomena in the physics of such systems, paying central attention to the novel manifestations of those. After shortly summarising the basic phenomena and their description, we concentrate on several specific directions in this field. One of them is the reduction of effective dimensionality in many systems with orbital degrees of freedom due to directional character of orbitals, with concomitant appearance of some instabilities leading in particular to the formation of dimers, trimers and similar clusters in a material. The properties of such cluster systems, largely determined by their orbital structure, are discussed in detail, and many specific examples of those in different materials are presented. Another big field which acquired special significance relatively recently is the role of relativistic spin-orbit interaction. The mutual influence of this interaction and the more traditional Jahn-Teller physics is treated in details in the second part of the review. In discussing all these questions special attention is paid to novel quantum effects in those.
“…The galvanostatic discharge test [50][51][52] was followed at very low C (0.2 C) rate to obtain the electrochemical parameters of the battery. C rate is defined as the ratio of the charge/ discharge current over the nominal capacity of the battery.…”
Section: Model Establishment: Galvanostatic Discharge Testmentioning
Over the past decade, there has been an exponential growth in the on-road electric vehicle (EV), hybrid electric vehicle (HEV), plug-in hybrid electric vehicle (PHEV), and their other counterparts making the total on-road vehicle number cross ten million by the end of 2020. [1] The factors responsible for this growth are supportive regulatory frameworks, economics, and the sustainability goals set forward by the countries. EVs are proved to be more efficient than conventional vehicles and reduce the reliance on conventional oil-based fuels, thereby reducing tailpipe emissions. There are still some roadblocks in the implementation of EVs, charging infrastructure, single-charge range, battery costs, life, performance, and safety, to name a few. Most of these can be traced back to the temperature sensitivity of the battery. Various subsystems govern the overall EV performance, the battery being the most crucial of those all. Li-ion battery is the most widely used option for the electrification of vehicles. The battery is subjected to various discharge current rates and environmental conditions. Discharge rate and ambient temperature dictate the battery temperature, which dictates its performance, life, and safety.At very low temperatures, the battery's performance is compromised. [2] At higher temperatures, on the other hand, the battery electrodes degrade faster, impacting the cycle and calendar life, even at times leading to a thermal runaway which results in safety issues. [3] The optimum temperature range for achieving the performance, life, and safety of Li-ion battery is established as 25-40 C. [4] Various battery thermal management systems are already in place and are continuously being researched to keep the battery within optimum temperature limits. [5] They include different passive and active approaches such as phase change material (PCM)-based thermal management system (TMS), [6,7] liquid mini channel cooling, [8,9] natural or forced air convection, [10] heat pipes [11] an many more. Research nowadays is focused on innovative combinations of passive and active thermal management approaches such as a combination of PCM with liquid cooling, [12] fins with air/PCM, [13] two-phase refrigerant cooling, [14] nanofluid with meshed PCM foam/porous metal foam, [15,16] and hydrogenbased cooling. [17] Various factors need to be addressed while designing the battery thermal management systems that include cooling system's dead-weight and power consumption, compactness, cost, packaging, compatibility, reliability, accessibility. Also, care needs to be taken not to over-design the battery thermal management system (BTMS) as the increased cost of power in running the BTMS may supersede the credit received for the improved performance. Hence, assessing the impact of discharge rate and ambient temperature on the battery's thermal and electrical performance is vital for the optimal design of a BTMS.
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