The x-T magnetic phase diagram of the La1-xYxMn2Ge2 system by neutron diffraction study

The La1-xYxMn2Ge2 (0 less than or equal to x less than or equal to 0.9) solid solution has been studied by neutron diffraction. This allows the construction of the x-T magnetic phase diagram of this system. Seven different magnetic structures, in which some are characterized by mixed (001) Mn planes where ferro- and antiferromagnetic components coexist, are necessary to describe this diagram. An antiferromagnetic Mn moment in-plane component occurs in all the studied compounds. This component gives rise to an incommensurate interplane arrangement, at least at low temperature, for the La1-xYxMn2Ge2 (0 less than or equal to x less than or equal to 0.7) compounds and to a commensurate arrangement for x = 0.2 and 0.1. The corresponding Neel temperatures decrease from T-N=421 K for x = 0 to T-N=377 K for x=0.8. The antiferromagnetic in-plane component appears only at relatively low temperatures in La0.1Y0.9Mn2Ge2. The ferromagnetic in-plane component gives rise to a ferromagnetic interplane arrangement for 0 less than or equal to x less than or equal to 0.7 (T-c approximate to 320 K) and to an antiferromagnetic interplane arrangement for 0.8 less than or equal to x less than or equal to 1 (T-N2 = 362-427 K). The total Mn moment value is large in the yttrium-poor compounds (mu(Mn)approximate to 3.0 mu(B)) and weaker in the yttrium-rich compounds (mu(Mn)approximate to 2.3 mu(B)). A full description of the Mn sublattice magnetic behaviour within the whole RMn(2)Ge(2) and (R,R')Mn2Ge2 series is given.