High Pressure-Driven Magnetic Disorder and Structural Transformation in Fe3 GeTe2 : Emergence of a Magnetic Quantum Critical Point.

Among the recently discovered 2D intrinsic van der Waals (vdW) magnets, Fe3 GeTe2 (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 Fe3 GeTe2 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 Pressure-Induced Polymorphic Transformations in Fluconazole.

The structural properties and Raman spectra of fluconazole have been studied by means of X-ray diffraction and Raman spectroscopy at pressures up to 2.5 and 5.5 GPa, respectively. At a pressure of 0.8 GPa, a polymorphic phase transition from the initial form I to a new triclinic form VIII has been observed. At higher pressure of P = 3.2 GPa, possible transformation into another new polymorphic form IX has been detected. The unit cell parameters and volumes, and vibration modes as functions of pressure have been obtained for the different forms of fluconazole.

The polymorphic phase transformations in the chlorpropamide under pressure.

The crystal structure and vibrational spectra of the chlorpropamide have been studied by means of the X-ray diffraction and Raman spectroscopy at pressures up to 24.6 and 4.4 GPa, respectively. Two polymorphic phase transitions, between initial orthorhombic form-A and a monoclinic form-AI at P ∼ 1.2 GPa and, in additional, to another monoclinic form-AII at P ∼ 3.0 GPa, were observed. At pressures above 9.6 GPa, a transformation to the amorphous phase of chlorpropamide was revealed. The lattice parameters, unit cell volumes, and vibration modes as functions of pressure were obtained for the different polymorphic modifications of chlorpropamide.