Origin of the high-temperature ferromagnetism in Co-doped PbPdO₂ semiconductors: A theoretical and experimental study

High-temperature ferromagnetism has always been a classic and interesting subject, especially in spin gapless semiconductor PbPdO$2$ with exotic properties. Here, a combination of theoretical and experimental studies was employed to clarify the origin of high Tc. First, based on first-principles calculations, electronic band structures of PbPd$0.875$Co$0.125$O$2$ at different Co substitution positions were studied. Our results indicate that Co atoms tend to form an antiferromagnetic ground state due to the Co–O–Co (180$°$⁠) indirect exchange effect, while ferromagnetism is favored in Co-doped PbPdO$2$ when a unique molecular field effect induced band crossover and $p$–$d$ coupling occurs. It is revealed that metallic or semiconductor properties have an important connection with ferromagnetism or antiferromagnetism. Subsequently, a Monte Carlo simulation was carried out based on the first-principles results to predict the ferromagnetism of PbPd$0.875$Co$0.125$O$2$⁠. Finally, the moment-magnetic field and moment-temperature curves were also measured for PbPd$0.875$Co$0.125$O$2$ samples, which was found well consistent with the theoretical findings. The ground state of PbPd$0.875$Co$0.125$O$2$ was confirmed to be ferromagnetic. Our results well explain the origin of high-temperature ferromagnetism in diluted magnetic semiconductors and provide new approaches for the design of future high Tc spintronic devices.