  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 (P -31c). 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.
