Low-temperature magnetic properties of Fe nanograins in an amorphous Fe-Zr-B matrix

The low-temperature magnetic behavior of Fe87Zr6B6Cu1 metallic glasses has been studied by dc magnetization (5-400 K) and RT Mossbauer spectroscopy after a series of thermal treatments. Precipitation of crystalline Fe nanograins is observed, their size (5-15 nm) and amount (1-19%) being dependent on the annealing temperature. The produced structural arrangement provides a model system in order to study the properties of a collection of high-moment ferromagnetic clusters embedded in a weak ferromagnetic matrix. The splitting between the zero-field-cooling and field-cooling magnetization curves increases as the amount of Fe grains does, up to about 6% of the sample volume, and then decreases. This is interpreted as an effect of exchange coupling between the grains through the surrounding amorphous matrix.