Phase segregation of MnP in chalcopyrite dilute magnetic semiconductors: A cautionary tale

On the basis of reports of room-temperature ferromagnetism in Mn-doped semiconductor chalcopyrites, we undertook an investigation of a new doped system, CdSnP2:Mn. CdSnP, heated with Mn powder in a tube furnace under flowing argon at 350 and 500 degrees C resulted in a material having ferromagnetic properties (T-c approximate to 290 K) closely resembling those reported for other Mn-doped chalcopyrites (e.g., CdGeP2, ZnGeP2). However, the appearance of weak MnP impurity peaks in the powder X-ray diffraction pattern for the 500 degrees C prepared sample, coupled with the strong similarity in the measured ferromagnetic behaviors, suggests that the ferromagnetic response may not be an intrinsic effect. Measurements on bulk and nanocrystalline MnP as well as on control samples prepared by heating CdP2 or red phosphorus with Mn powder lead to the conclusion that (i) heating mixtures of CdSnP2 with Mn results in phase-segregated MnP, a room-temperature ferromagnetic material, and (ii) amounts as small as 0.3 wt % (1.0 mol %) MnP, well below the resolution of powder X-ray diffraction, are sufficient to dominate the magnetic response in these chalcopyrite materials.