Magnetic order in a quenched-high-temperature-phase of Cu-doped MnBi

Permanent magnets are of great importance due to their vast applications. MnBi has been proposed to be a potential permanent magnet that can be widely used while past efforts have been focused on optimizing the ferromagnetic low-temperature phase of MnBi. Herein, we report a series of new materials, CuxMn1-xBi, crystallizing in a quenched high-temperature-phase (QHTP) MnBi-related structure. We synthesized single crystals of CuxMn1-xBi and found that they crystallize in an unreported trigonal structure (P31c). Magnetic properties measurements imply high-temperature antiferromagnetic (AFM) ordering and low-temperature ferromagnetic or ferrimagnetic (FM/FiM) ordering. By analyzing the doping effect on crystal structure and magnetic properties, we established a magnetic phase diagram for Cu-doped MnBi and attributed the AFM and FM/FiM to two different atomic sites of Mn. Cu-doped MnBi crystals adopt a new type of high-temperature phase of the well-known permanent magnet, MnBi. The magnetic diagram demonstrates the evolution of magnetic orders along with increasing concentration of Cu in such a system.