Beijing National Laboratory for Condensed Matter Physics and Institute of Physics, Chinese Academy of Sciences, Beijing 100190, China.
School of Physical Sciences, University of Chinese Academy of Sciences, Beijing 100190, China.
Phys Rev Lett. 2019 Jul 26;123(4):047201. doi: 10.1103/PhysRevLett.123.047201.
The n-type HgCr_{2}Se_{4} exhibits a sharp semiconductor-to-metal transition (SMT) in resistivity accompanying the ferromagnetic order at T_{C}=106 K. Here, we investigate the effects of pressure and magnetic field on the concomitant SMT and ferromagnetic order by measuring resistivity, dc and ac magnetic susceptibility, as well as single-crystal neutron diffraction under various pressures up to 8 GPa and magnetic fields up to 8 T. Our results demonstrate that the ferromagnetic metallic ground state of n-type HgCr_{2}Se_{4} is destabilized and gradually replaced by an antiferromagnetic, most likely a spiral magnetic, and insulating ground state upon the application of high pressure. On the other hand, the application of external magnetic fields can restore the ferromagnetic metallic state again at high pressures, resulting in a colossal magnetoresistance (CMR) as high as ∼ 3×10^{11}% under 5 T and 2 K at 4 GPa. The present study demonstrates that n-type HgCr_{2}Se_{4} is located at a peculiar critical point where the balance of competition between ferromagnetic and antiferromagnetic interactions can be easily tipped by external stimuli, providing a new platform for achieving CMR in a single-valent system.
n 型 HgCr_{2}Se_{4} 在电阻率中表现出尖锐的半导体-金属转变（SMT），伴随着 T_{C}=106 K 时的铁磁有序。在这里，我们通过测量电阻率、直流和交流磁化率以及单晶中子衍射，研究了压力和磁场对伴随 SMT 和铁磁有序的影响，实验压力最高可达 8 GPa，磁场最高可达 8 T。我们的结果表明，n 型 HgCr_{2}Se_{4} 的铁磁金属基态在外加高压下失稳，并逐渐被反铁磁态取代，很可能是螺旋磁态和绝缘态。另一方面，施加外磁场可以在高压下再次恢复铁磁金属态，导致在 4 GPa 下 2 K 时 5 T 下高达 ∼ 3×10^{11}%的巨大磁电阻（CMR）。本研究表明，n 型 HgCr_{2}Se_{4} 位于一个特殊的临界点，铁磁和反铁磁相互作用之间的竞争平衡可以很容易地被外部刺激打破，为在单价体系中实现 CMR 提供了一个新的平台。
