Magnetic phase diagram of the solid solution LaMn 2 (Ge 1-x Si x ) 2 (0 ≤ x ≤ 1) unraveled by powder neutron diffraction.

The structural and magnetic properties of the ThCrSi-type solid solution LaMn(GeSi) (x = 0.0 to 1.0) have been investigated employing a combination of X-ray diffraction, magnetization and neutron diffraction measurements, which allowed establishing a magnetic composition-temperature phase diagram. Substitution of Ge by Si leads to a compression of the unit cell, which affects the magnetic exchange interactions. In particular, the magnetic structure of LaMn(GeSi) is strongly affected by the unit cell parameter c, which is related to the distance between adjacent Mn layers. Commensurate antiferromagnetic layers and a canted ferromagnetic structure dominate the Si-rich part of the solid solution, whilst an incommensurate antiferromagnetic flat spiral and a conical magnetic structure are observed in the Si-poor part.