Effect of Mn on the collapse of ‘‘ferromagnetic’’ order in melt-spun Fe90Zr10 amorphous alloys (abstract)

Abstract

It is well known that amorphous Fe-rich binary Fe-Zr alloys exhibit two magnetic transitions as a function of decreasing temperatures. For example, it is found that an amorphous melt-spun Fe90Zr10 alloy has a ‘‘ferromagnetic’’ transition at about 230 K which is then followed at low temperatures by a loss of long-range order into a spin-glass-like state at around 12 K. The question arises as to the role of Zr in the unusual properties of binary amorphous alloys containing as much as 90 at. % Fe. In order to gain further insight into the above, we have carried out low-field ac susceptibility as well as dc magnetization studies in both low and high applied fields on melt-spun Fe90−xMnxZr10 alloys for 0≤x≤22 at. % Mn. The amorphicity of all the alloys were checked by using x-ray techniques. On substituting Fe with Mn, initially the Curie temperature is unaffected but the spin-freezing temperature Tfg decreases. At higher concentrations of Mn (above 10 at. %) TC decreases at the rate of 30 K/at. % Mn while Tsg begins to increase to temperatures above 50 K as determined from the peak in the quadrature component of the ac susceptibility. Thus the magnetic properties of Fe-Mn-Zr alloys appear to be mainly determined by the exchange coupling among Fe, Fe-Mn, and Mn-Mn atoms with Zr playing the role of simple glass-forming element. Detailed hysteretic loop studies will also be presented. Finally, we shall compare the above results with those obtained on substituting Fe with Ni and a light rare-earth Pr.