Magnetic phase diagrams of amorphous (Ni_100-xFe_x)-metalloid alloys: The key role of the electronic density of states at the Fermi level for the onset of magnetic order

Highlights: • Magnetic phase diagrams for amorphous Ni-Fe-metalloid systems were analyzed. • Critical Fe content for the onset of FM order scales inversely with Fermi level DOS. • Interpretation in terms of the Stoner enhancement of the iron-free amorphous matrices. - Abstract: There have been extended studies on the appearance of ferromagnetism in transition-metal–metalloid (MD) glasses. In particular, the paramagnetic (PM) to ferromagnetic (FM) transition has been investigated on numerous (Ni_100-xFe_x)-MD alloys upon the introduction of Fe where MD can represent a combination of various metalloid elements, while keeping the metal/metalloid ratio constant. It has been reported that adding a sufficient amount of Fe to a Pauli PM Ni-MD alloy matrix first induces a spin-glass (SG) state at low temperatures which goes over to a PM state at higher temperatures. Beyond a certain Fe content, x_c, the SG state transforms to a FM state upon increasing the temperature. By plotting the characteristic transition temperatures as a function of the Fe content, a magnetic phase diagram can be constructed for each Ni-Fe-MD system which has a multicritical point (MCP) at x_c. By using the reported magnetic phase diagrams of various Ni-Fe-MD alloy systems, it is shown that the critical Fe content, x_c scales inversely with the density of states at the Fermi level, N(E_F), of the parent Ni-MD matrix. This means that the higher the N(E_F), the lower the critical Fe content to induce ferromagnetism in the Ni-MD matrix. This is then discussed in terms of the Stoner enhancement factor, S, which characterizes the tendency of the matrix to become ferromagnetic.