The x − T magnetic phase diagram of the La 1− xY xMn 2Ge 2 system by neutron diffraction study

Abstract

The La 1− x Y x Mn 2Ge 2 (0⩽x⩽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 La 1− x Y x Mn 2Ge 2 (0⩽x⩽0.7) compounds and to a commensurate arrangement for x = 0.2 and 0.1. The corresponding Néel temperatures decrease from T N = 421K for x = 0 to T N = 377K for x = 0.8. The antiferromagnetic in-plane component appears only at relatively low temperatures in La 1− x Y x Mn 2Ge 2. The ferromagnetic in-plane component gives rise to a ferromagnetic interplane arrangement for0⩽x⩽0.7 ( T N ≈ 320K) and to an antiferromagnetic interplane arrangement for0.8⩽x⩽1 (T N = 362–427K). The total Mn moment value is large in the yttrium-poor compounds (μ Mn ≈ 3.0μ N) and weakr in the yttrium-rich compounds (μ Mn ≈ 2.3 μ N). A full description of the Mn sublattice magnetic behaviour within the whole RMn 2Ge 2 and (R,R′)Mn 2Ge 2 series is given.