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 $-\frac{\mathrm{dM}}{\mathrm{dc}}$ vary with the electron to atom ratio $\mathfrak{z}$ of the transition metal: They show a maximum near $\mathfrak{z}\simeq 8.3$, as does the Slater-Pauling curve, and decrease to $-\frac{\mathrm{dM}}{\mathrm{dc}}\simeq \frac{3.0{\mu }_B}{\left(\mathrm{Al}\mathrm{atom}\right)}$ near pure nickel. At concentrations close to pure Fe, there is a sharp drop to $-\frac{\mathrm{dM}}{\mathrm{dc}}=\frac{2.2{\mu }_B}{\left(\mathrm{Al}\mathrm{atom}\right)}$. The moment decrease due to the Al solute is found to be in qualitative accord with $M=M_0\mathrm{}(1-c)-c(V-n_s){\mu }_B$, where $-(V-n_s){\mu }_B$ is the moment induced by an impurity atom with valence $V$ in the surrounding transition matrix with free-electron density $n_s$. This law takes for Ni as a particular case the known form $M=M_0-cV{\mu }_B$. In the (Fe-Cr)-Al series the observed magnetic behavior is correlated with electronic-specific-heat data and critical concentrations for appearance of ferromagnetism.