Even though pure metallic manganese is closely allied to the ferromagnetic family of iron, cobalt, and nickel, it is paramagnetic to temperatures as low as -259" C. Therefore, at ordinary temperatures, manganese never attains the magnetic "strength" of iron, cobalt and nickel. Theoretically the existence of ferromagnetism in solids depends on a quantity known as the mutual magnetic exchange energy. This in turn depends on the ratio of the distance of closest approach of two atoms in the solid to the radius of an incomplete inner shell ("3," shell) of electrons in the atom.
If this ratio of distances is greater than 1.5 the mutual exchange energy is positive and the solid is ferromagnetic; if the ratio is less than 1.5, the energy is negative and the solid is not ferromagnetic.
For iron, cobalt and nickel it is greater than 1.5 and for manganese it is less than 1.5 ; the former are then, as is well known, ferromagnetic, while the latter is not.
From the preceding, one might conclude that by increasing the separation between manganese atoms, the ratio of atomic separation to "3d" radius could be altered favorably, and the result would be a ferromagnetic material containing manganese, AAtomic separation of this kind can be accomplished by alloying manganese with a nonmagnetic element. Ferromagnetic ternary alloys of copper, aluminum, and manganese (Heusler alloys) are typical examples of the existing magnetic manganese alloys and compounds, Dilute binary noble metal-manganese alloys (i.e., alloys containing a small amount of manganese as the solute metal) have not been widely reported.
However, this laboratory has been conducting an investigation of the thermoelectric properties of dilute noble metaltransition metal alloys. During this work, non-linear deviations in the temperature dependence of the electrical resistivity, characteristic of ferromagnetic metals and alloys, were observed for those containing manganese.
Normally this dependence for clilute alloys is linear over a fairly wide temperature range. For noble metal alloys containing more than 8 at. ye Mn the deviations occur as marked changes in