Tuning the magnetic properties of quasi-2D van der Waals material Fe_2.7GeTe₂ with pressure

It has been recently shown that the magnetic properties of the van der Waals (vdW) ferromagnet Fe_3-xGeTe₂ can be tuned via electric fields, strain, and more recently high pressure. In this work, we examine the pressure effect on the magnetism in Fe deficient Fe_2.7GeTe₂. Magnetic susceptibility results show a decrease in the magnetic ordering temperature from 154.78 K (1 bar) to 141.87 K (1.22 GPa). X-ray magnetic circular dichroism (XMCD) also saw a decrease in the magnetic ordering nearly vanishing at approximately 19.1 GPa. Pressure dependent Raman spectroscopy was performed at room temperature and showed a redshift in the Tellurium peaks (~120 and ~140 cm^-1) at 4.9 GPa. The spectrum abruptly changes at 7.9 GPa remaining the same until the highest pressure of 13.3 GPa is reached. Optical images show at 7.6 GPa, Fe_2.7GeTe₂ undergoes phase transition causing it to become dull grey in color. Upon decompression, the Te peaks returned and the shiny physical appearance of Fe_2.7GeTe₂ returned as well. This work demonstrates the significance of employing the external pressure in tuning the magnetic and optical properties of van der Waals magnets.