Browsing by Author "Hutchison, WD"

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    Magnetic structures of R2Fe2Si2C intermetallic compounds: Evolution to Er2Fe2Si2C and Tm2Fe2Si2C
    (American Physical Society, 2019-05-20) Susilo, RA; Rocquefelte, X; Cadogan, JM; Bruyer, E; Lafargue-Dit-Hauret, W; Hutchison, WD; Avdeev, M; Ryan, DH; Namiki, T; Campbell, SJ
    The magnetic structures of Er2Fe2Si2C and Tm2Fe2Si2C (monoclinic Dy2Fe2Si2C-type structure, C2/m space group) have been studied by neutron powder diffraction, complemented by magnetization, specific heat measurements, and 166Er Mössbauer spectroscopy, over the temperature range 0.5 to 300 K. Their magnetic structures are compared with those of other R2Fe2Si2C compounds. Antiferromagnetic ordering of the rare-earth sublattice is observed below the Néel temperatures of TN=4.8(2)K and TN=2.6(3)K for Er2Fe2Si2C and Tm2Fe2Si2C, respectively. While Er2Fe2Si2C and Tm2Fe2Si2C have the same crystal structure, they possess different magnetic structures compared with the other R2Fe2Si2C (R = Nd, Gd, Tb, Dy, and Ho) compounds. In particular, two different propagation vectors are observed below the Néel temperatures: k=[12,12,0] (for Er2Fe2Si2C) and k=[0.403(1),12,0] (for Tm2Fe2Si2C). For both compounds, the difference in propagation vectors is also accompanied by different orientations of the Er and Tm magnetic moments. Although the magnetic structures of Er2Fe2Si2C and Tm2Fe2Si2C differ from those of the other R2Fe2Si2C compounds, we have established that the two magnetic structures are closely related to each other. Our experimental and first-principles studies indicate that the evolution of the magnetic structures across the R2Fe2Si2C series is a consequence of the complex interplay between the indirect exchange interaction and crystal field effects. ©2019 American Physical Society
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    Spin-reorientation in quaternary Dy_2Fe_2Si_2C
    (Australian Institute of Nuclear Science and Engineering, 2016-11-30) Susilo, RA; Cadogan, JM; Hutchison, WD; Stewart, GA; Campbell, SJ; Avdeev, M
    The low temperature magnetic properties of Dy_2Fe_2Si_2C have been investigated by magnetisation, specific heat, neutron powder diffraction and "5"7Fe Mössbauer spectroscopy measurements. In contrast to other R_2Fe_2Si_2C compounds, we found that Dy_2Fe_2Si_2C undergoes two successive magnetic transitions at low temperatures. The first magnetic transition at T_N = 26(2) K is associated with the transition from paramagnetic to antiferromagnetic states, whereas our neutron diffraction and "5"7Fe Mössbauer spectroscopy studies reveal that the second magnetic transition at T_t = 6(2) K is likely related to a spin-reorientation of the Dy moments rather than the independent ordering of the Fe sublattice. The magnetic structure above T_t can be described with a propagation vector k = [0 0 1/2] with the ordering of the Dy magnetic moments along the monoclinic b-axis, whereas on cooling below T_t the Dy moment tips away from the b-axis towards the ac-plane. Magnetocrystalline anisotropy energy calculations show that a canted magnetic structure is more energetically favourable below T_t than b-axis order due to the important influence of higher-order crystal field terms at low temperatures, thus explaining the unique occurrence of spin reorientation in Dy_2Fe_2Si_2C compared with other R_2Fe_2Si_2C compounds.