Evolution from 4f-electron antiferromagnetic to ferromagnetic order in the CeCu(Ge 1−x Sn x Ge1−xSnx ) alloy series (0≤x≤1 0≤x≤1 ) of Evolution from 4f-electron antiferromagnetic to ferromagnetic order in the CeCu(Ge 1−x Sn x Ge1−xSnx ) alloy series (0≤x≤1 0≤x≤1 )