Two-dimensional van der Waals (2D vdW) magnets have attracted great attention recently and possess the unprecedented advantages of incorporating high-quality vdW heterostructures and homostructures into spintronic devices, and exploring various physical phenomena or technologies. Among them, Fe₅GeTe₂ (F5GT) has ferromagnetic order close to room temperature, however the magnetic properties near its intrinsic transitions and F5GT-based 2D devices remain mostly unexplored. Here, we systematically demonstrate the peculiar magnetic properties of Fe₅GeTe₂ nanoflakes near its intrinsic transition temperature (T_p) which is far lower than its Curie temperature (T_C) of ~ 265 K, and firstly discover anomalous magnetoresistance effect in F5GT homo-junctions by magneto-transport measurements. The strongest anomalous Hall effect occurs around T_p which is located in a temperature range from 130 to 160 K for the F5GT nanoflakes with different thicknesses. Furthermore, negative magnetoresistance (N-MR) and butterfly-shaped magnetoresistance (B-MR) are observed in F5GT homo-junction devices, and they appeared only in an intermediate temperature range from 110 to 160 K, noticeably showing the maxima near the T_p rather than the lowest temperature. Our experimental results clearly reveal the significant influence of intrinsic transitions on magnetic properties of F5GT and magnetoresistance effect in F5GT homo-junction devices, which imply a new strategy to achieve high-performance 2D spintronic devices by tuning intrinsic magnetic or structural transitions in 2D vdW magnets.

The morphology manipulation of nanomaterials by ion irradiation builds a way to precisely control physicochemical properties. Under the continuous irradiation of low energy Ga⁺, Ne⁺, and He⁺ ions, an ion compaction effect has been found in hollow FePt nanochains with ultrathin shell that the volumes of the nanochains are gradually compacted by ions. The deep learning algorithm has been successfully applied to automatically and precisely measure average sizes of spheres in hollow FePt nanochains. The compaction under ion irradiation is very fast in the very early period and then proceeds to a slow region. The compaction rates in both regions are linearly fitted and all the values are in the order of 10^–17 to 10^–14 cm²/ion. Ion species and ion current have effect on the compaction rate. For example, the compaction rate of Ga⁺ ions is larger than those of Ne⁺ and He⁺ ions under an identical current, while irradiation with larger current can compact nanochains faster. The ion compaction effect originates from the local shear deformation caused by the interaction between incident ions and the electrons of Fe and Pt atoms in the ultrathin shell. With continuous irradiation, the crystalline clusters of FePt nanchains firstly grow larger and then become amorphous. The ion compaction effect can be applied to tune the size and crystal structure of hollow structures with a precise rate by choosing appropriate ion species and current.

Tunable behavior in electrocatalysis by external multifields, such as magnetic field, thermal field, and electric field, is the most promising strategy to expand the theory, design, and synthesis of state-of-the-art catalysts and the cell in the near future. Here, a systematic investigation for the effect of external magnetic field and thermal field on methanol oxidation reactions (MOR) in magnetic nanoparticles is reported. For Co₄₂Pt₅₈ truncated octahedral nanoparticles (TONPs), the catalytic performance in MOR is greatly increased to the maximum of 14.1% by applying a magnetic field up to 3000 Oe, and it shows a monotonical increase with increasing working temperature. The magnetic enhanced effect is closely related to the Co content of Co_xPt_100-x TONPs. Furthermore, the enhancement effect under a magnetic field is more obvious for Co₄₂Pt₅₈ TONPs annealed at 650 ℃. First-principle calculation points out that the magnetic fields can facilitate the dehydrogenation of both methanol and water by suppression of entropy of the electron spin and lowering of the activation barrier, where OH_ad intermediates on Co sites play a more important role. The application of magnetic fields together with thermal fields in MOR provides a new prospect to manipulate the performance of direct methanol fuel cells, which will accelerate their potential applications.

Pt-based magnetic nanocatalysts are one of the most suitable candidates for electrocatalytic materials due to their high electrochemistry activity and retrievability. Unfortunately, the inferior durability prevents them from being scaled-up, limiting their commercial applications. Herein, an antiferromagnetic element Mn was introduced into PtCo nanostructured alloy to synthesize uniform Mn-PtCo truncated octahedral nanoparticles (TONPs) by one-pot method. Our results show that Mn can tune the blocking temperature of Mn-PtCo TONPs due to its antiferromagnetism. At low temperatures, Mn-PtCo TONPs are ferromagnetic, and the coercivity increases gradually with increasing Mn contents. At room temperature, the Mn-PtCo TONPs display superparamagnetic behavior, which is greatly helpful for industrial recycling. Mn doping can not only modify the electronic structure of PtCo TONPs but also enhance electrocatalytic performance for methanol oxidation reaction. The maximum specific activity of Mn-PtCo-3 reaches 8.1 A·m^-2, 3.6 times of commercial Pt/C (2.2 A·m^-2) and 1.4 times of PtCo TONPs (5.6 A·m^-2), respectively. The mass activity decreases by only 30% after 2, 000 cycles, while it is 45% and 99% (nearly inactive) for PtCo TONPs and commercial Pt/C catalysts, respectively.