CHANGING THE MAGNETISM OF AMORPHOUS FeSiB BY MECHANICAL MILLING

We have studied the magnetic properties of a sample obtained by high-energy mechanical milling from a ferromagnetic FeSiB amorphous ribbon [1]. The milled material mainly consists of a Fe-based amorphous matrix embedding a minor fraction of alpha-Fe nanocrystallites (~23%). The magnetic behavior features magnetization dynamics effects that have been ultimately ascribed to the local modification, induced by milling, of the interatomic distance distribution in the Fe-based amorphous matrix, which changes its magnetic properties: a new magnetic phase originates, with low temperature spin-glass like properties (speromagnetic), namely with a magnetic character completely different from that of the precursor ferromagnetic amorphous ribbon. We propose that speromagnetic regions and regions of the amorphous matrix that have maintained the ferromagnetic nature coexist inside the milled sample, also together with the alpha-Fe nanocrystallites. As a consequence of the magnetic dishomogeneity, at T ~ 50 K the milled FeSiB system undergoes a transition from a low temperature disordered frozen state, similar to a spin-cluster-glass, to a high temperature regime where ferromagnetism predominates. [1] L. Del Bianco, F. Spizzo, M. Tamisari, E. Bonetti, F. Ronconi, D. Fiorani, J. Phys.: Condens. Matter. 22, 296010 (2010)