Nanocrystalline alloys studied by positron annihilation lifetime spectroscopy

Nanocrystalline alloys present a new class of materials that exhibit interesting magnetic properties. These stem primarily from the presence of crystalline grains with the size of several tens of nanometers embedded in a residual amorphous matrix. In this paper, we employ positron annihilation spectrometry to investigate the relation between positron lifetime and microstructure of the NANOPERM-type metallic Fe76Mo8Cu1B15 alloy. The behaviour of positron lifetime with respect to the annealing temperature is discussed for samples, which were prepared by one hour thermal treatment in a vacuum at temperatures ranging from 330 up to 700 °C. Samples in amorphous (as-quenched) state were analysed, too. The results of this work confirm that the optimum annealing temperature of 550 °C correlates with the minimum of free volume and coincide with the temperature at which superior magnetic properties are observed. (© 2007 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)