Pressure-Tunable Crystal Structure and Magnetic Transition Temperature of the Nowotny Chimney-Ladder CrGeγ Phase

A Nowotny chimney-ladder (NCL) chromium germanide (CrGe gamma) with varying compositions has been synthesized under high pressure. Crystal structure parameters of the NCL CrGe gamma have been calculated by Le Bail refinement based on the superspace group. The refined gamma of CrGe gamma increases with the synthesis pressure, indicating an increasing Ge content. The NCL CrGe gamma phases are ferromagnetic at T = 2 K regardless of their composition, and the magnetic transition temperature (T-C) increases when the gamma becomes higher. It is noteworthy that CrGe1.763 and CrGe1.774 synthesized at P = 10 and 14 GPa have magnetic transition temperatures of T = 295 and 333 K above room temperature, respectively. Surprisingly, the magnetic transition temperature has changed by Delta T-C = 270 K, although the gamma values of the raw material and the sample synthesized at P = 14 GPa differ by only Delta gamma = 0.05, corresponding to an atomic concentration of 0.62 atom %. The synthesis pressure acts as an essential parameter in tuning the composition of the NCL phase. Accordingly, the high-pressure synthesis may significantly control several physical characteristics of NCL phases by utilizing compositional and structural modulation.

Automated summary

Nowotny chimney-ladder (NCL) chromium germanide (CrGe gamma) with varying compositions has been synthesized under high pressure, showing different crystal structure parameters and magnetic properties depending on the synthesis pressure. The synthesis pressure plays a significant role in tuning the composition and physical characteristics of NCL phases.