MAGNETIC-PROPERTIES OF FEALN FILMS AT ELEVATED-TEMPERATURES

FeAlN films were fabricated by reactive sputtering from an Fe alloy ta rget in a nitrogen containing plasma. By varying the nitrogen content in the films, magnetic moment as high as 20 kG and coercivities less t han 1 Oe can be achieved at room temperature. However, it has been obs erved that the soft properties of these films experience a reversible degradation at elevated measuring temperatures. The critical temperatu re, T-0(c), defined as the temperature at which the coercivity doubles , generally decreases as more nitrogen is incorporated into the film. T-0(c) agrees well with the temperature where remanent squareness (B-r /B-s) equals 0.83, indicating a reduced intergranular exchange couplin g in films. However, T-0(c) is far below either the reported Curie tem perature of the gamma'-Fe4N phase or that of the alpha-Fe phase, which are found in these films. It is suggested that an interfacial granula r phase between the grain boundaries of alpha-Fe or gamma'-Fe4N crysta llites is responsible for the low T-0(c). When the temperature increas es above T-0(c), the interfacial phase becomes paramagnetic, and the e xchange interaction between crystalline grains becomes weak, thereby c ausing the coercivity increases. (C) 1997 American Institute of Physic s.