Gadolinium Doping Gallium Nitride Clusters: First-principles Study

Diluted magnetic semiconductors pave the way for realizing spintronics. In recent years,gadolinium-doped GaN has attracted great interests. In this paper, using First-principlescalculations, we made a systematic research on Gd-doped GanNnclusters, explored the magneticcoupling mechanism between gadolinium atoms and discussed the colossal magnetic moment.The first part, we studied the magnetic coupling mechanism using First-principlescalculations. Gadolinium is a very special magnetic element, but for now, there is much less workon its magnetic coupling mechanism. Our calculations indicate that there is a magnetic phasetransition from antiferromagnetism to ferromagnatism as the interatomic distance increasing. Forshort distances the ground state is antiferromagnetic, but it changes to ferromagnetic at d=2.2.This conclusion is high valuable in practical applications and theoretical researches. The evolutionof density of states (DOS) of4f electrons demonstrated that the indirect exchange interactiongradually dominate with the increasing interatomic distance, this is the foundation offerromagnetism. In addition, the relationship between ΔEFM-AFMand interatomic distance is notcompletely monotonic.The second part, we made a systematic research on Gd-doped GanNnclusters usingFirst-principles calculations. We find Gd-doped GanNnclusters always hold a a magnetic momentof7μB, no matter how the cluster size and structure change. This indicates4f electrons of Gd,which is located on different potential fields and surroundings, always stay parallel arrangement.Therefore, the energy of exchange interaction between4f electrons of Gd is very high. It iscompletely different with the3f electrons of transition metal (TM), which is easy affected by thepotential fields or ligand fields. This indicates again that gadolinium is of great value inapplication because of its unique magnetic properties. In addition, we find N and Ga arespin-polarized in the Gd-doped GanNnclusters. Moreover, spin-polarization of N is stronger farthan that of Ga. In conclusion, researches on geometric construction and its evolution of Gd-dopedGanNnclusters contribute to understand the growth mechanisms of GaN:Gd. Electronic andmagnetic researches on the microscopic nanostructures make contribution to understanding theorigin of the room temperature ferromagnetism and the colossal magnetic moment phenomenonoccurred on GaN:Gd.The third part, we discussed how to explain the colossal magnetic moment phenomenon.Based on analyzing the experimental data, we present how to explain the colossal magnetic moment phenomenon by the spin-polarization of N and Ga. Our demonstration indicates thisexplanation is reasonable and practical. And this explanation provides new perspective andsolution for similar problems.