Individual Co site contributions to the magnetic anisotropy and NMR investigation of ${\mathrm{Y}}_2{\left({\mathrm{Co}}_{1-x}{M}_x\right)}_{17}$ ($M=\mathrm{C}\mathrm{u},\mathrm{A}\mathrm{l}$)

Co-site crystalline fields in Y${\mathrm{Co}}_5$ and ${\mathrm{Y}}_2$ ${\mathrm{Co}}_{17}$ are calculated using a point-charge model. It is shown that the $2c$ site in Y${\mathrm{Co}}_5$ and the $18j$ site in ${\mathrm{Y}}_2$ ${\mathrm{Co}}_{17}$ make positive contributions to the magnetic anisotropy, while the $3g$ site in Y${\mathrm{Co}}_5$ and the $18h$, $9d$, and $6c$ sites in ${\mathrm{Y}}_2$ ${\mathrm{Co}}_{17}$ make negative contributions, in agreement with Streever's NMR result. Through an NMR investigation, $M$ substitution for Co in ${\mathrm{Y}}_2{\left({\mathrm{Co}}_{1-x}{M}_x\right)}_{17}$ ($M=\mathrm{C}\mathrm{u},\mathrm{A}\mathrm{l}$) is demonstrated to occur at random in $M=\mathrm{Cu}$ and with a site preference in $M=\mathrm{Al}$. Al is found mainly to prefer a $6c$ dumbbell site. Consequently, it is shown that the different magnetic anisotropy behaviors between ${\mathrm{Y}}_2{\left({\mathrm{Co}}_{1-x}{\mathrm{Cu}}_x\right)}_{17}$ and ${\mathrm{Y}}_2{\left({\mathrm{Co}}_{1-x}{\mathrm{Al}}_x\right)}_{17}$ arise from the differences in site preference between Cu and Al for Co.