Applied magnetism
2025, 74 (23): 237201.
doi: 10.7498/aps.74.20251162
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2025, 74 (23): 237501.
doi: 10.7498/aps.74.20251317
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Magnetic refrigeration technology, featuring environmental friendliness, energy efficiency and high performance, is recognized as a next-generation refrigeration technology with the potential to replace gas compression refrigeration technology. However, current magnetic refrigeration materials typically exhibit an excessively narrow phase transition temperature range (≤10 K), thus necessitating the stacking of materials with multiple compositions to meet the practical refrigeration temperature span. In this study, the typical La(Fe, Si)13-based magnetic refrigeration material is selected, and an innovative gradient laser powder bed fusion technology is adopted to obtain 3D-print La0.70Ce0.30Fe11.65–xMnxSi1.35 alloys with horizontal compositional gradients (where the Mn content varies continuously from 0 to 0.64). Systematic characterization of their microstructures, magnetic properties, and magnetocaloric effects indicates that this technology enables a controllable gradient distribution of compositions along the powder bed plane and high-throughput preparation, thereby achieving a continuous variation of the Curie temperature of the gradient alloy over a wide temperature range from 134 K to 174 K. With the increase of Mn content, the phase transition of the alloy gradually changes from a weak first-order phase transition to a second-order phase transition, and the peak shape of the magnetic entropy change curve shifts from “sharp and high” to “broad and flat”. The full width at half maximum of the temperature range is extended to 83.3 K, allowing the gradient alloy to maintain high refrigeration capacity (RC ~130 J/kg, 3 T) at all time. This study breaks through the bottlenecks of traditional material preparation and performance via gradient additive manufacturing, providing a novel technical pathway for achieving high-throughput preparation and performance optimization of magnetic refrigeration materials.
2025, 74 (23): 237502.
doi: 10.7498/aps.74.20251210
Abstract +
Hydrogenation or protonation provides a feasible pathway for exploring exotic physical functionality and phenomena within correlated oxide system through introducing an ion degree of freedom. This breakthrough provides great potential for enhancing the application of multidisciplinary equipment in the fields of artificial intelligence, related electronics and energy conversions. Unlike traditional substitutional chemical doping, hydrogenation enables the controllable and reversible control over the charge-lattice-spin-orbital coupling and magnetoelectric states in correlated system, without being constrained by the solid-solution limits. Our findings identify proton evolution as a powerful tuning knob to cooperatively regulate the magnetoelectric transport properties in correlated oxide heterojunction, specifically in metastable VO2(B)/La0.7Sr0.3MnO3(LSMO) systems grown via laser molecular beam epitaxy (LMBE). Upon hydrogenation, correlated VO2(B)/LSMO heterojuction undergoes a reversible magnetoelectric phase transition from a ferromagnetic half-metallic state to a weakly ferromagnetic insulating state. This transition is accompanied by a pronounced out-of-plane lattice expansion due to the incorporation of protons and the formation of O—H bonds, as confirmed by X-ray diffraction (XRD). Proton evolution extensively suppresses both the electrical conductivity and ferromagnetic order in the pristine VO2(B)/LSMO system. Remarkably, these properties recover through dehydrogenation via annealing in an oxygen-rich atmosphere, underscoring the high reversibility of hydrogen-induced magnetoelectric transitions. Spectroscopic analyses, including X-ray photoelectron spectroscopy (XPS) and synchrotron-based soft X-ray absorption spectroscopy (sXAS), provide further insights into the physical origin underlying the hydrogen-mediated magnetoelectric transitions. Hydrogen-related band filling in the d-orbital of correlated oxides accounts for the electron localization in VO2(B)/LSMO heterostructure through hydrogenation, while the suppression of the Mn3+-Mn4+ double exchange leads to the magnetic transitions. This work not only expands the hydrogen-related phase diagram for correlated oxide system but also establishes a versatile pathway for designing exotic magnetoelectric functionalities via ionic evolution, which has great potential for developing protonic devices.
