Magnetic structure of UCu2Si2 and U(Cu0.75Mn0.25)2Si2

The replacement of Cu by Mn in UCu2Si2 causes surprisingly large increases in both the Curie temperature and the coercivity of this ferromagnetic material. We have performed neutron powder diffraction experiments on a series of U(Cu,Mn)2Si2 alloys and found that UCu2Si2 is a simple ferromagnet with a magnetic moment of 2.0(1)μB on the U atoms pointing along the crystallographic c axis of the tetragonal unit cell. The alloy U(Cu0.75Mn0.25)2Si2 is also a ferromagnet with moments on both U and Mn pointing in the c direction. The moment on the U atoms is 1.7(1)μB, and the average moment on the (Cu,Mn) site is 0.16(5)μB. No indication of chemical ordering on the (Cu,Mn) site was detected.