Among the recently discovered 2D intrinsic van der Waals (vdW) magnets, Fe3GeTe2 (FGT) has emerged as a strong candidate for spintronics applications, due to its high Curie temperature (130 – 220 K) and magnetic tunability in response to external stimuli (electrical field, light, strain). Theory predicts that the magnetism of FGT can be significantly modulated by an external strain. However, experimental evidence is needed to validate this prediction and understand the underlying mechanism of strain‐mediated vdW magnetism in this system. Here, the effects of pressure (0 – 20 GPa) are elucidated on the magnetic and structural properties of Fe3GeTe2 by means of synchrotron Mössbauer source spectroscopy, X‐ray powder diffraction and Raman spectroscopy over a wide temperature range of 10 – 290 K. A strong suppression of ferromagnetic ordering is observed with increasing pressure, and a paramagnetic ground state emerges when pressure exceeds a critical value, PPM ≈ 15 GPa. The anomalous pressure dependence of structural parameters and vibrational modes is observed at PC ≈ 7 GPa and attributed to an isostructural phase transformation. Density functional theory calculations complement these experimental findings. This study highlights pressure as a driving force for magnetic quantum criticality in layered vdW magnetic systems.

The stoichiometry value x of WO x , or its oxidation state, is crucial for improving performances of the hole-selective contact heterojunction silicon solar cell. However, it is challenging to tune the films' oxidation state using the well-known evaporation method. In this study, a simulation was performed to analyze the effect of x on short-circuit current (J sc ) loss, attributed to the holeselective contact in the device. Compared to the thickness of WO x layer, x has a more important role in minimizing J sc loss. Based on the simulation, the WO x /c-Si heterojunction solar cells having hole-selective WO x contacts with tuned x to vary its oxidation state were fabricated using reactive magnetron sputtering. The relationships of the open-circuit voltage (V oc ) and J sc with respect to x were similar. The experimentally determined J sc increased from 34.7 to 36.6 mA cm −2 when x was increased from 2.72 to 2.77; this result is consistent with the simulation. Nevertheless, fill factor (FF) reduced with the increase of x, owing to the reduced conductivity of WO x . Both oxidation state and film conductivity must be as high as possible to simultaneously achieve high V oc , J sc , and FF. The lowest x yielded a solar cell efficiency of 13.3%.

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