The magnetocrystalline anisotropy constants of two ferromagnetic intermetallic compounds, YCo
5and Y
2Co
17, have been measured at room temperature. YCo
5has a magnetically easy

axis and

erg/cm
3; K
2has not been determined but is estimated to be less than 10
6erg/cm
3. Y
2Co
17has an easy basal plane, and, by three different methods of measurement :

erg/cm
3;

erg/cm
3,

erg/cm
3;

erg/cm
3,

erg/cm
3.