Study on Absence of Room-Temperature Ferromagnetism in the Mn-AlN Films With Various Mn Concentrations

We have investigated the magnetic behavior and structure of polycrystalline Mn-AlN (Al_1-xMn_xN) films with various Mn concentrations (x= 0.05-0.24) fabricated by reactive direct current (dc) magnetron sputtering. The magnetic behavior of these films depends on the Mn concentration x. The films with x=0.05-0.10 show a paramagnetic behavior at 10-300 K. The film with x=0.17 shows remanent magnetization and coercivity only at 10 K, while that with x=0.24 shows an unknown magnetic behavior. Only wurtzite-type AlN phase is observed for x below 0.10. The coexistence of a wurtzite-type AlN phase and a secondary phase such as Al-Mn alloy, Mn-nitride, or Al-Mn-N ternary compound is observed for x= 0.17. The coexistence of a wurtzite-type AlN phase and a ThH₂-type Mn₃N₂ phase is observed for x=0.24. From these results, it is concluded that the Al_1-xMn_xN films do not exhibit room-temperature (RT) ferromagnetism for all x . Moreover, it is likely that the ferromagnetic behavior observed at 10 K for x=0.17 is caused by the secondary phase.