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

Abstract

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.

Commented review: UCu2Ge2and UCu2Si2—compounds with only ferromagnetic ordering

“…Their neutron-diffraction study showed ferromagnetic ordering below T C = 103(3) K and down to 4.2 K, with uranium magnetic moments along the c axis. They correlated their neutron-diffraction observations with their magnetization measurements in an applied field of 1 T, which also indicated ferromagnetic ordering below a comparable temperature of 107 K. Shortly afterwards Hiebl and Rogl [31] studied an annealed polycrystalline sample of UCu 2 Si 2 by magnetization measurements (shown for applied fields of 1.00 and 1.18 T) and found only ferromagnetic ordering below T C = 105 K and down to 1.8 K. At the same time Giorgi et al [32] studied a polycrystalline sample (with no annealing details) of UCu 2 Si 2 by neutron-diffraction and magnetization measurements and confirmed its ordering as a simple ferromagnet. Later on Hiebl et al [33] studied an annealed stoichiometric polycrystalline sample of UCu 2 Si 2 , which was well characterized, by magnetization measurements (shown for an applied field of 0.1 T) and found only ferromagnetic ordering below T C = 105(5) K and down to 2 K. They emphasized the role of movements of the narrow domain walls in the magnetization processes (as mentioned above, generally in section 2 and for UCu 2 Ge 2 in section 3).…”