Thermally-induced co-existence of superparamagnetism and spin-glass like behavior in undoped amorphous AlN thin film

Abstract

The co-existence of superparamagnetism (SPM) and spin-glass (SG) behavior in undoped amorphous AlN thin film is reported for the first time. The as-deposited AlN film exhibits only SPM behavior while post-deposition annealing at 850 °C for 4 h in a high vacuum of 2 × 10−6 mbar induces SG signature along with SPM. GIXRD measurement confirms the amorphous nature of AlN in as-deposited and annealed films. EDX, RRBS, and XPS measurements indicate the presence of nitrogen vacancies which are drastically enhanced after annealing. The magnetic hysteresis loop for annealed film elucidates the existence of soft and hard magnetic phases attributed to the presence of SPM and SG states, respectively. Temperature-dependent magnetization, magnetization relaxation, and Arrott plot confirm the presence of SG state. Based on the observations and the analysis, the thermally induced enhancement of nitrogen vacancies present in AlN are attributed to be responsible for the co-existence of the SPM and SG state.