Investigation on the structure and magnetic properties at low temperature for nanocrystalline γ′-Fe4N thin films

Nanocrystalline gamma'-Fe4N thin films were synthesized on single crystal Si (10 0) substrate by facing target magnetron sputtering at a mixture of Ar/N-2 gas discharge, and their structure, morphology, and magnetic properties at room temperature and low temperature were characterized using X-ray diffraction (XRD), scanning electron microscopy (SEM), and vibrating sample magnetometer (VSM), respectively. The results showed that the films were gamma'-Fe4N with an average grain size of 55 nm, which had a highly preferred orientation along (111). The ratio of remanent magnetization M-t over saturated magnetization M-s at room temperature for gamma'-Fe4N was 0.528, which indicated that the films had a single easy magnetized direction. In the temperature range of 80-350 K, the saturation magnetization M-s and coercive force H-c increased, whereas the ratio of M-r/M-s decreased with decreasing temperature. The relation between the coercive force H-c and temperature T observed a T-1/2 law, and the coercivity at T=0 K of 356.87 Oe and blocking temperature of 667 K were acquired, respectively. However, the relation between M-s and T did not observe the Bloch T-3/2 law, which meant that the interaction among spin waves should be considered. Through fitting M-s-T equation, the saturation magnetization at T=0 K of 202 emu/g, Bloch constant of 1.0 x 10(-4) K-3/2, and exchange interaction constant of 1.537 x 10(-21) were obtained, respectively. (c) 2007 Elsevier B.V. All rights reserved.