Magnetic-Competition-Induced Colossal Magnetoresistance in n-Type HgCr2Se4 under High Pressure*

HgCr₂Se₄ is a well-known ferromagnetic(FM) semiconductor with T_C = 106 ~ 120 K¹ and it has received renewed interest recently. Here, we performed the first comprehensive high-pressure study on n-type HgCr₂Se₄ single crystals and surprisingly found that the FM metallic ground state is destabilized and gradually replaced by an antiferromagnetic (AF) insulating ground state under high pressure. Our combined magnetic susceptibility and neutron measurements under high pressure indicated that the AF order is most likely a spiral-type. On the other hand, the application of external magnetic fields can restore the FM metallic state again at high pressures, resulting in a colossal magnetoresistance as high as ~ 3 ^ 10¹¹ % under 5 T and 2 K at 4 GPa. Our results demonstrate that HgCr₂Se₄ situates at a critical point where the competition between FM and AF exchange interactions can be easily tuned by pressure and magnetic field. Thus, our work provides a means for realizing novel state where the extremely large magnetoresistance can be obtained via switching between two distinct electronic ground states in a single-valent system².
1. P. K. Baltzer et al., Phys. Rev. Lett. 1965, 15, 493
2. J. P. Sun et al., Phys. Rev. Lett. 2019, 123, 047201