Percolation Phenomena in Amorphous Iron-Nickel Alloys.
Magnetization data, covering a wide range of temperatures and applied fields, are reported for the series of amorphous alloys (Fe(,p)Ni(,1-p))(,80)P(,20). The iron-rich alloys are shown to be good ferromagnets, with the expected ferromagnetic critical behavior. Nickel, however, serves as a paramagnetic diluent. The amorphous structure permits the production of alloys that span the entire concentration range from paramagnetic (p = 0) to ferromagnetic (p = 1). The phase diagram has the features expected for a dilute ferromagnet. The low-temperature approach to magnetic saturation is a function of concentration. The more dilute alloys do not fully saturate. These results are not explained by percolation scaling theories. Scaling models for the large clusters are not relevant when large applied fields are used. We calculate the magnetization using the distribution function for the number of small clusters in a percolating magnet. This calculation agrees with the data, and shows that small clusters play an important role in the bulk properties of a dilute magnet. Complex models involving competing interactions are not required to explain the concentration dependence of the approach to saturation. Various parameters describing the excitation of spin waves were extracted from the magnetization data. There has been a great deal of theoretical work on the problem of spin waves in dilute magnets. The data are consistent with current models based on a fractal description of the infinite cluster.
- Pub Date:
- Physics: Condensed Matter