Magnetic properties of amorphous GdFeB and GdCoB alloys

Studies have been made of the magnetization of GdFeB and GdCoB amorphous thin films in which ratios of Gd to transition metal and B to transition metal were varied. In GdCoB alloys the Co moment decreases as the sum of the B and Gd concentration increases. Assuming a charge transfer mechanism, each Gd contributes 1.4 electrons and each B 2.1 electrons to the Co 3-d band. The moment can be described by an additive charge transfer equation. However, in GdFeB alloys the Fe moment increases with increasing B concentration beyond a boron to iron ratio of 0.15. In addition to a reduction in Fe moment by charge transfer of 2.1 electrons from Gd and 2.4 from B, there is an increase in Fe moment due to B addition at higher concentrations. A possible cause for this behavior can be found in the noncollinear (sperimagnetic) alignment of the Fe magnetic sublattice in amorphous ferrimagnetic alloys. High field susceptibility data show that sperimagnetism is reduced with increasing boron.