From ferromagnetic to helical order with a discussion of the low-temperature antiferromagnetism in composite Cd1–xMnxGeP2+MnP semiconductors

Abstract

Mn-doped chalcopyrites exhibit rich and unique physical properties due to the presence of magnetic clusters, both at ambient and under high external pressures. Despite recent efforts and rich literature on this topic, it is still necessary to explain some of the phenomena occurring in these systems, such as the origin of magnetic interactions at ambient pressure. In this context, we report the investigations of physical mechanisms responsible for the magnetic order of a ${\mathrm{Cd}}_{1--x}{\mathrm{Mn}}_{x}\mathrm{Ge}{\mathrm{P}}_{2}+\mathrm{MnP}$ composite system with changeable Mn contents $x$, ranging from 0.008 to 0.037. The presence of MnP clusters, confirmed by energy dispersive x-ray spectrometry and scanning electron microscopy methods, is responsible for the ferromagnetic phase transition with the Curie temperature ${T}_{\mathrm{C}}$ around 295 K. Moreover, the transition from ferromagnetic to helical order is observed, with the critical temperature ${T}_{\mathrm{S}}$ changing from 78 K for the sample with $x=0.008$ down to 54 K for $x=0.037$. Besides the common explanation based on the structural disorder at the cluster surface and finite-size effects, we associate the observed ${T}_{\mathrm{S}}(x)$ dependence with the local pressure effect due to Mn doping, where the influence of the external pressure $P\ensuremath{\sim}0.25\phantom{\rule{0.16em}{0ex}}\mathrm{GPa}$ corresponds to the influence of the Mn content $x=0.035$.