Magnetovolume effects in metamagnetic itinerant-electron systems Y(Co1-xAlx)2 and Lu(Co1-xGax)2

High-field magnetization and magnetostriction measurements have been performed for typical metamagnetic itinerant-electron systems Y(Co1-xAlx)(2) and Lu(Co1-xGax)(2) with 0 less than or equal to x less than or equal to 0.12 at 4.2 K in pulsed magnetic fields up to 40 T. The substitution of Al or Ga for Co significantly decreases the critical field of the metamagnetic transition. The magnetovolume coupling constant n(dd) in the paramagnetic state is nearly constant up to about x = 0.05 and then decreases with increasing x. Moreover, the value of n(dd) is considerably reduced by the metamagnetic transition. The variation of n(dd) produced by the change of x or the metamagnetic transition is considered to originate from the change of the spin fluctuation spectrum.