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Modifying the crystal structure and corresponding functional properties of complex oxides by regulating their oxygen content has promising applications in energy conversion and chemical looping, where controlling oxygen migration plays an important role. Therefore, finding an efficacious and feasible method to facilitate oxygen migration has become a critical requirement for practical applications. Here, we report a compressive-strain-facilitated oxygen migration with reversible topotactic phase transformation (RTPT) in La0.5Sr0.5CoO x films based on all-solid-state electrolyte gating modulation. With the lattice strain changing from tensile to compressive strain, significant reductions in modulation duration (∼72%) and threshold voltage (∼70%) for the RTPT were observed, indicating great promotion of RTPT by compressive strain. Density functional theory calculations verify that such compressive-strain-facilitated efficient RTPT comes from significant reduction of the oxygen migration barrier in compressive-strained films. Further, ac-STEM, EELS, and sXAS investigations reveal that varying strain from tensile to compressive enhances the Co 3d band filling, thereby suppressing the Co–O hybrid bond in oxygen vacancy channels, elucidating the micro-origin of such compressive-strain-facilitated oxygen migration. Our work suggests that controlling electronic orbital occupation of Co ions in oxygen vacancy channels may help facilitate oxygen migration, providing valuable insights and practical guidance for achieving highly efficient oxygen-migration-related chemical looping and energy conversion with complex oxides.

By utilizing the large lattice distortion caused by incommensurate cone-spiral magnetic ordering and the induced texture effect in Fe-doped MnNiGe alloys, NTE largely exceeding the average crystallographical contribution has been achieved.

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Solid-state refrigeration based on caloric effect has been regarded as an attractive alternative to the conventional gas compression technique. Boosting the caloric effect of a system to its optimum is a long-term pursuit. Here, we report enhanced magnetocaloric effect (MCE) and barocaloric effect (BCE) by hydrostatic pressure in La(Fe 0.92 Co 0.08 ) 11.9 Si 1.1 with a NaZn 13 -type structure. The entropy change ΔS MCE is almost doubled under 11.31 kbar, while the ΔS BCE is more than tripled under 9 kbar. To disclose the essence from the atomic level, neutron powder diffraction studies were performed. The results revealed that hydrostatic pressure sharpens the magnetoelastic transition and enlarges the volume change, ΔV/V, during the transition through altering the intraicosahedral Fe−Fe bonds rather than the inter-icosahedral distances in the NaZn 13 -type structure. First-principles calculations were performed, which offers a theoretical support for the enlarged caloric effect related to the evolution of phase transition nature. Moreover, the enhanced lattice entropy change was calculated by Debye approximation, and a reliable way to evaluate BCE is demonstrated under a high pressure that DSC cannot reach. The present study proves that remarkable caloric effect enhancement can be achieved through tackling specific atomic environments by physical pressure, which may also be used to tailor other pressure-related effects, such as controllable negative thermal expansion.

The multicaloric effect refers to the thermal response of a solid material driven by simultaneous or sequential application of more than one type of external field. For practical applications, the multicaloric effect is a potentially interesting strategy to improve the efficiency of refrigeration devices. Here, the state of the art in multi-field driven multicaloric effect is reviewed. The phenomenology and fundamental thermodynamics of the multicaloric effect are well established. A number of theoretical and experimental research approaches are covered. At present, the theoretical understanding of the multicaloric effect is thorough. However, due to the limitation of the current experimental technology, the experimental approach is still in progress. All these researches indicated that the thermal response and effective reversibility of multiferroic materials can be improved through multicaloric cycles to overcome the inherent limitations of the physical mechanisms behind single-field-induced caloric effects. Finally, the viewpoint of further developments is presented.

Spin structure of a magnetic system results from the competition of various exchange couplings. Pressure-driven spin structure evolution, through altering interatomic distance, and hence, electronic structure produces baromagnetic effect (BME), which has potential applications in sensor/actuator field. Here, we report a new spin structure(CyS-AFM b ) with antiferromagnetic(AFM) nature in Fe-doped Mn 0.87 Fe 0.13 NiGe. Neutron powder diffraction (NPD) under in situ hydrostatic pressure and magnetic field was conducted to reveal the spin configuration and its instabilities. We discovered that a pressure higher than 4 kbar can induce abnormal change of Mn(Fe)−Mn(Fe) distances and transform the CyS-AFM b into a conical spiral ferromagnetic(FM) configuration(45°-CoS-FM a ) with easily magnetized but shortened magnetic moment by as much as 22%. The observed BME far exceeds previous reports. Our first-principles calculations provide theoretical supports for the enhanced BME. The compressed lattice by pressure favors the 45°-CoS-FM a and significantly broadened 3d bandwidth of Mn(Fe) atoms, which leads to the shortened magnetic moment and evolution of spin structure.

The cyclability and frequency dependence of the adiabatic temperature change (ΔT ad ) under an alternating magnetic field (AMF) are significantly important from the viewpoint of refrigeration application. Our studies demonstrated, by direct measurements, that the cyclability and low-magnetic-field performance of ΔT ad in FeRh alloys can be largely enhanced by introducing second phases. The ΔT ad under a 1.8 T, 0.13 Hz AMF is reduced by 14%, which is much better than that (40−50%) of monophase FeRh previously reported. More importantly, the introduction of second phases enables the antiferromagnetic−ferromagnetic phase transition to be driven by a lower magnetic field. Thus, ΔT ad is significantly enhanced under a 0.62 T, 1 Hz AMF, and its value is 70% larger than that of monophase FeRh previously reported. Although frequency dependence of ΔT ad occurs, the specific cooling power largely increases by 11 times from 0.17 to 1.9 W/g, as the frequency increases from 1 to 18.4 Hz under an AMF of 0.62 T. Our analysis of the phase transition dynamics based on magnetic relaxation measurements indicates that the activation energy barrier is lowered owing to the existence of second phases in FeRh alloys, which should be responsible for the reduction of the driving field. This work provides an effective way to enhance the cyclability and lowmagnetic-field performance of ΔT ad under an AMF in FeRh alloys by introducing second phases.