Structures and magnetic properties of gold-coated transition-metal clusters [Mn
13@Au
20]
- and [Co
13@Au
20]
- are studied within the framework of gradient-corrected density functional theory. The gold coating can result in either an enhanced or an attenuated effect on the magnetism of the core clusters. For [Mn
13@Au
20]
-, the total magnetic moment is greatly enhanced to as high as 44
B, more than 20-fold higher than that of the bare Mn
13- cluster. For [Co
13@Au
20]
-, however, the gold coating gives rise to an attenuation effect which leads to a reduction of the magnetic moment to 20
B from 30
B of the bare Co
13- cluster.