Magnetic phase diagram of the solid solution LaMn2(Ge1-xSix)(2) (0 <= x <= 1) unraveled by powder neutron diffraction

The structural and magnetic properties of the ThCr2Si2-type solid solution LaMn2(Ge1-xSix)(2) (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 LaMn2(Ge1-xSix)(2) 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.