Magnetic behavior of the Hf(Fe1−xAlx)2 system (abstract)

Abstract

Magnetic properties of pseudobinary compounds Hf(Fe1−xAlx)2 have been investigated as a function of temperature and concentration in the range 0≤x≤0.60. The present work is motivated to understand the role of Hf in the system, compared to the systems Y(Fe1−xAlx)2 and Zr(Fe1−xAlx)2, where freezing phenomena characteristic of a cluster-glass regime can be observed in the Y case in the concentration range 0.1≤x≤0.35.1 The magnetization measurements are made as a function of temperature and static magnetic applied field. The system shows a mixture of a C14 (hexagonal) and a C15 (cubic) Laves phase structures from x=0 up to x<0.15; for x≥0.15, only the C14 hexagonal phase is present. The Curie temperature TC decreases with Al concentration and tends to TC=0 about x=0.60. We have observed an irreversible behavior of the magnetization curves as a function of temperature when the samples are cooled with (FC) and without (ZFC) an external field, up to temperatures near TC. In the low-temperature range the magnetization drops with temperature for ZFC measurements. No saturation was observed even in high magnetic fields up to 80 kOe, indicating a high anisotropy energy. An S-type behavior is observed in the initial experiments for high Al concentrations (40% and 50%) and low temperatures. A great decrease of the coercive field with increase of temperature is also observed; for 50% Al, this dependence can be fitted by an exponential. All the phenomena can be explained by domain wall pinning. The difference between ZFC and FC curves is related to the rapid decrease of the magnetic hardness by thermal activation as the temperature increases. A magnetic phase diagram is presented.