Gap and magnetic engineering via doping and pressure in tuning the colossal magnetoresistance in (Mn${}_{1-x}$Mg${}_x$)${}_3$Si${}_2$Te${}_6$

Abstract

Ferrimagnetic nodal-line semiconductor Mn${}_3$Si${}_2$Te${}_6$ keeps the records of colossal magnetoresistance (CMR) and angular magnetoresistance (AMR). Here we report tuning the electronic transport properties via doping and pressure in (Mn${}_{1-x}$Mg${}_x$)${}_3$Si${}_2$Te${}_6$. As the substitution of nonmagnetic Mg${}^{2+}$ for magnetic Mn${}^{2+}$, ferrimagnetic transition temperature $T_C$ gradually decreases, while the resistivity increases significantly. At the same time, the CMR and AMR are both enhanced for the low-doping compositions (e.g., $x=0.1$ and 0.2), which can be attributed to doping-induced broadening of the band gap and a larger variation range of the resistivity when undergoing a metal-insulator transition by applying a magnetic field along the $c$ axis. On the contrary, $T_C$ rises with increasing pressure due to the enhancement of the magnetic exchange interactions until a structural transition occurs at $\sim$13 GPa. Meanwhile, the activation gap is lowered under pressure and the magnetoresistance is decreased dramatically above 6 GPa where the gap is closed. At 20 and 26 GPa, evidences for a superconducting transition at $\sim$5 K are observed. The results reveal that doping and pressure are effective methods to tune the activation gap, and correspondingly, the CMR and AMR in nodal-line semiconductors, providing an approach to investigate the magnetoresistance materials for novel spintronic devices.

5 pages, 5 figures