Tuning ZrFe₄Si₂ by Ge and Y substitution

The intermetallic compound series AFe₄X₂ (A = Y, Lu, Zr; X = Si, Ge) presents a rare case of magnetic frustrated metallic systems. In particular ZrFe₄Si₂ is of strong interest because our results indicate this system to be very close to a quantum critical point (QCP) where Fe magnetic order disappears. To get a deeper insight into its ground state, we performed a detailed study of Ge and Y substituted ZrFe₄Si₂. The isovalent substitution of Ge for Si induces a negative chemical pressure as Ge is larger than Si. As expected from this, the substitution results in the formation of a well-defined antiferromagnetic order with Neel temperatures increasing up to 25 K at 40 % Ge. This confirms ZrFe₄Si₂ to be extremely close to the QCP, just on the magnetic side of it. With the second substitution series Y_xZr_1-xFe₄Si₂ we investigate the development from the highly reduced antiferromagnetic order in ZrFe₄Si₂ towards the two magnetic transitions at 56 K and 76 K, which we see in YFe₄Si₂.