Phase relations, crystal chemistry, and physical properties of MgZn2-type Laves phases in the Mn-Cu-Si and Mn-Ni-Si systems

In this study, we present the phase relations, crystal structure, and physical properties of the MgZn2-type Laves phases in the Mn-Cu-Si and Mn-Ni-Si systems. Our results evidence that the homogeneous regime of the Laves phase in the Mn-Cu-Si system at 800 degrees C ranges from 32.5 to 36.7 at.% Mn and from 11.5 to 13.5 at.% Si, indicating the Laves phase in this system having an ideal stoichiometry AB(2), inconsistent with previous reports. For structural and physical property investigations, two alloys with compositions MnCu1.65Si0.35 and MnNi1.25Si0.75 are considered. In both alloys, Mn atoms are preferably situated at the 4f site and Cu(Ni) and Si share the 2a and 6h sites. Both are antiferromagnets with T-N approximate to 800 K for MnCu1.65Si0.35 and T-N approximate to 630 K for MnNi1.25Si0.75. Rietveld refinements of the room-temperature neutron diffraction data demonstrate that in both cases only the Mn atoms carry magnetic moments, which are aligned antiferromagnetically along the c axis. The magnetic moments at room temperature are 2.7 mu(B)/Mn for MnCu1.65Si0.35 and 2.9 mu(B)/Mn for MnNi1.25Si0.75, respectively. The magnetic properties are confirmed by transport, magnetization, NMR measurements, and band-structure calculations.