Magnetization Measurements of 0, 5, 10, and 20 at.% Al- Substituted First-Transition-Series Alloys

Precision measurements on saturation moments of Cr-Fe, Fe-Co, Fe-Ni, and Co-Ni alloys with 0, 5, 10, and 20 at.% Al substitutions are reported; they show linear decrease of the mean atomic moment M at low Al concentration c. The negative slopes -dM/dc vary with the electron to atom ratio z of the transition metal: They show a maximum near z8.3, as does the Slater-Pauling curve, and decrease to -dM/dc3.0μB(Alatom) near pure nickel. At concentrations close to pure Fe, there is a sharp drop to -dM/dc=2.2μB(Alatom). The moment decrease due to the Al solute is found to be in qualitative accord with M=M₀(1-c)-c(V-nₛ)μB, where -(V-nₛ)μB is the moment induced by an impurity atom with valence V in the surrounding transition matrix with free-electron density nₛ. This law takes for Ni as a particular case the known form M=M₀-cVμB. In the (Fe-Cr)-Al series the observed magnetic behavior is correlated with electronic-specific-heat data and critical concentrations for appearance of ferromagnetism.