Magnetic phases in Ge-Fe thin films containing high Fe content

Magnetic phases in evaporated thin films of Ge_100-xFe _x (x in at.%) alloys with x ≤ 36.6 and 51.8 are examined. At x ≤ 36.6, a single amorphous phase is formed. The magnetic phase at room temperature appears to be ferromagnetic, and it transforms into a spin-glass phase at 20K. The magnetic phases are more complicated at the higher Fe composition of x ≤ 51.8, which is mainly due to the presence of Fe precipitates in the amorphous matrix. An analysis based on the superparamagnetism indicates that the effective composition of the amorphous phase is estimated to be x ≤ 39.4, and this amorphous phase shows a similar magnetic behaviour to that observed in the x ≤ 36.6 sample with the exception of a slightly higher spin freezing temperature of 30K. Due to the Fe precipitates, an additional superparamagnetic behaviour is observed with a blocking temperature of 160K. Magnetization saturation in the spin-glass state occurs at a relatively small applied field, which indicates that the direct antiferromagnetic exchange coupling between Fe ions is weak.