Magnetic properties of the $3d$ transition metals in the amorphous ternary alloys: ${\mathrm{Gd}}_{0.2}{\left({\mathrm{Fe}}_x{\mathrm{Co}}_{1-x}\right)}_{0.8}$, ${\mathrm{Gd}}_{0.2}{\left({\mathrm{Co}}_x{\mathrm{Ni}}_{1-x}\right)}_{0.8}$, and ${\mathrm{Gd}}_{0.2}{\left({\mathrm{Fe}}_x{\mathrm{Ni}}_{1-x}\right)}_{0.8}$

A systematic study was made of the magnetic properties of the amorphous alloys: ${\mathrm{Gd}}_{0.2}{\left({\mathrm{Fe}}_x{\mathrm{Co}}_{1-x}\right)}_{0.8}$, ${\mathrm{Gd}}_{0.2}{\left({\mathrm{Co}}_x{\mathrm{Ni}}_{1-x}\right)}_{0.8}$, and ${\mathrm{Gd}}_{0.2}{\left({\mathrm{Fe}}_x{\mathrm{Ni}}_{1-x}\right)}_{0.8}$. Results indicate that GdCo, GdNi, and GdCoNi alloys are collinear ferrimagnets involving electron transfer from Gd to the $3d$ elements. However, GdFe, GdFeNi, and GdFeCo alloys containing less than 30% Co are sperimagnetic due to antiferromagnetic interactions in the Fe subnetwork. Mean-field exchange energies are calculated and used to explain the results. A Slater-Pauling-type curve is constructed, and the dependence of properties on the average number of transition-metal $3d$ electrons is discussed.