Magnetic ordering in HoFe6Ge6 studied by neutron diffraction

Abstract

Abstract The crystal structure and magnetic ordering of HoFe 6 Ge 6 annealed at 800°C are studied by neutron powder diffraction. The crystal structure consists of the host (Fe, Ge) and guest (Ho/Ho* and Ge/Ge*) subsystems. In view of the complex magnetic ordering the guest subsystem was preferably described as using two types of microdomain with a 1:3 volume ratio. In the first type of microdomain (I) the guest subsystem is fully disordered (average YCo 6 Ge 6 structure); in the second type (II) it is fully ordered (TbFe 6 Sn 6 superstructure, wave vector q =(1/2 1/2 0) of the orthohexagonal average structure). The limited coherence of microdomains leads to an anisotropic broadening of the satellites and can be described within a needle-like model (infinite ‖ [100] and small ⊥ [100]) with a mean correlation length 84(6) A. The Fe-moments order antiferromagnetically below T N ≈450 K with the wave vector q 1 =(1 0 0) in the superstructure basis for both types of microdomain. The Fe-moments point along a and are arranged into ferromagnetic (1 0 0) layers stacked (+ - + -⋯) along the a -axis. The 1.5 K Fe ordered moment value is 1.80(7) μ B /Fe. The Ho-moments order antiferromagnetically below 9 K with two wave vectors q 1 =(1 0 0) and q 2 =(1/3 0 0) in the superstructure basis. The q 1 wave vector is associated with microdomain I and gives rise to a collinear arrangement of the Ho moments along a . The q 2 wave vector corresponds to microdomain II and leads to a modulated arrangement of the Ho moments within the (0 yz ) plane. The 1.5 K ordered moment values are 6.0(8) μ B /Ho (I) and 2.0(4) μ B /Ho (II). The antiferromagnetic Ho–Ho correlations have limited spatial extent with the mean correlation length 95(30) A (I) and 70(30) A (II).