Browsing by Author "Susilo, RA"

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    Magnetic order and spin-reorientation in HoGa
    (IOP Publishing, 2012-01-01) Susilo, RA; Muñoz-Pérez, S; Cobas, R; Cadogan, JM; Avdeev, M
    We have determined the magnetic structure of the intermetallic compound HoGa by high-resolution neutron powder diffraction. This compound crystallizes in the orthorhombic (Cmcm) CrB-type structure and the magnetic structure comprises ferromagnetic order of the Ho sublattice along the c-axis. The Curie temperature is 66(3) K. Upon cooling below 20 K, the Ho magnetic moments cant away from the c-axis towards the ab-plane. At 3 K, the Ho moment is 8.8(2) μB and the Ho magnetic moments point in the direction θ = 30(2)° and phgr = 49(4)° with respect to the crystallographic c-axis. The observation of an ab-plane component at around 50° from the a-axis is in contrast with the suggested magnetic structure of ac order (θ = 32° and phgr = 0°) reported by Delyagin et al. [1] on the basis of a 119Sn Mössbauer spectroscopy study of a Sn-doped HoGa sample. However, we find that these two sets of orientations are in fact indistinguishable by Mössbauer spectroscopy. © Copyright 2021 IOP Publishing
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    Magnetic order and spin-reorientations in RGa (R = Dy, Ho and Er) intermetallic compounds
    (Australian Institute of Physics, 2013-02-06) Susilo, RA; Cadogan, JM; Ryan, DH; Lee-Horne, NR; Cobas, R; Muñoz-Pérez, S; Rosendahl-Hansen, B; Avdeev, M
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    Magnetic order and structural properties of Tb2Fe2Si2C
    (Elsevier, 2016-01-05) Susilo, RA; Cadogan, JM; Hutchison, WD; Avdeev, M; Cobas, R; Muñoz-Pérez, S; Campbell, SJ
    The structural and magnetic properties of Tb2Fe2Si2C have been investigated by bulk measurements (magnetisation and specific heat), X-ray diffraction, neutron powder diffraction and 57Fe Mössbauer spectroscopy over the temperature range 3 K–300 K Tb2Fe2Si2C is antiferromagnetic with a Néel temperature TN of 44(2) K. The magnetic structure can be described with a propagation vector k = [0 0 ] with the Tb magnetic moments ordering along the b-axis. We also observed strong magnetoelastic effects in particular along the a- and c-axes associated with the antiferromagnetic transition. The 57Fe Mössbauer spectra show no evidence of magnetic splitting down to 10 K, indicating that the Fe atom is non-magnetic in Tb2Fe2Si2C. © 2015 Elsevier B.V.
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    Magnetic ordering in Er2Fe2Si2C and Tm2Fe2Si2C
    (Australian Institute of Physics, 2015-02) Susilo, RA; Cadogan, JM; Hutchison, WD; Campbell, SJ; Avdeev, M; Ryan, DH; Namiki, T
    The magnetic ordering of two members of the R2Fe2Si2C (R = rare-earth) series of compounds (monoclinic Dy2Fe2Si2C-type structure with the C2/m space group), Er2Fe2Si2C and Tm2Fe2Si2C, have been studied by neutron powder diffraction and 166Er Mössbauer spectroscopy, complemented by magnetisation and specific heat measurements. In both cases, antiferromagnetic ordering of the R sublattice is observed, with Neel temperatures of 4.8(2) K and 2.6(3) K for Er2Fe2Si2C and Tm2Fe2Si2C, respectively. The magnetic structures of the Erand Tm-based compounds are quite different from those found for the other members of the R2Fe2Si2C series. Previous studies show that the common magnetic structure of the heavy- R2Fe2Si2C compounds involves ordering of the R sublattice along the b-axis with a propagation vector k = [0, 0, ½]. However, the antiferromagnetic structure of the Er sublattice in Er2Fe2Si2C is described by k = [½, ½, 0] with the Er magnetic moments lying close to the ac-plane. Tm2Fe2Si2C is found to exhibit a more complex magnetic structure that is characterised by a square-wave modulation of the Tm magnetic moments along the a-axis and a cell-doubling along the b-axis with k = [0.403(1), ½, 0]. The differences in the magnetic structures of these compounds are interpreted in terms of the RKKY exchange interaction, which depends on the R-R interatomic distances, and crystal field effects acting on the R3+ ions.
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    Magnetic ordering in Ho2Fe2Si2C
    (American Institute of Physics, 2015-02-23) Susilo, RA; Cadogan, JM; Cobas, R; Hutchison, WD; Avdeev, M; Campbell, SJ
    We have used neutron diffraction and 57Fe M€ossbauer spectroscopy, complemented by magnetisation and specific heat measurements, to examine the magnetic ordering of Ho2Fe2Si2C. We have established that Ho2Fe2Si2C orders antiferromagnetically below TN¼ 16(1) K with a magnetic structure involving ordering of the Ho sublattice along the b-axis with a propagation vector k ¼ ½0 0 12. 57Fe M€ossbauer spectra collected below TN show no evidence of a magnetic splitting, demonstrating the absence of long range magnetic ordering of the Fe sublattice. A small line broadening is observed in the 57Fe spectra below TN, which is due to a transferred hyperfine field—estimated to be around 0.3 T at 10 K—from the Ho sublattice. VC 2015 AIP Publishing LLC.
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    Magnetic structure and spin reorientation of quaternary Dy2Fe2Si2C
    (IOP Publishing, 2017-02-07) Susilo, RA; Cadogan, JM; Hutchison, WD; Stewart, GA; Avdeev, M; Campbell, SJ
    We have investigated the low temperature magnetic properties of Dy2Fe2Si2C by using magnetisation, specific heat, x-ray diffraction, neutron powder diffraction and 57Fe Mössbauer spectroscopy measurements over the temperature range 1.5 K–300 K. Dy2Fe2Si2C exhibits two magnetic transitions at low temperatures: an antiferromagnetic transition at ${{T}_{\text{N}}}\sim 26$ K and a spin-reorientation transition at ${{T}_{t}}\sim 6$ K. The magnetic structure above Tt can be described with a propagation vector $\mathbf{k}~=~\left(0~0~\frac{1}{2}\right)$ with the ordering of the Dy magnetic moments along the monoclinic b-axis whereas on cooling below Tt the Dy moment tips away from the b-axis towards the ac-plane. We find that the spin-reorientation in Dy2Fe2Si2C is mainly driven by the competition between the second-order crystal field term B20 and the higher-order terms, in particular B40 and B64. © 2017 IOP Publishing Ltd
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    The magnetic structure of Er 2MgGe 2
    (Australian Institute of Nuclear Science and Engineering, 2013-12-03) Susilo, RA; Cadogan, JM; Campbell, SJ; Suen, NT; Bobev, S; Avdeev, M
    A series of Mg-based germanides, R_2MgGe_2 have been synthesized with the heavy R elements. They crystallize in the tetragonal Mo_2FeB_2-type structure with the P4/mbm space group. The R_2MgGe_2 compounds are antiferromagnets with Neel temperatures ranging from 150 K (R = Gd) to 13 K (R = Sm). However, no sign of magnetic order has been observed for Er_2MgGe_2 and Tm_2MgGe_2, down to 5 K. Electronic structure calculations on Gd_2MgGe_2 suggest that the magnetic order of tnese compounds might be more complex than a simple collinear antiferromagnetism. In this report, we present our neutron diffraction studies of Er_2MgGe_2 to search for magnetic order and to determine the magnetic structure if order is indeed observed. We find that Er_2MgGe_2 orders antiferromagnetically at ~4 K. At 3 K, the magnetic structure can be described by a propagation vector of k = ["1/_2, "1/_2, "1/_4], with the Er magnetic moments forming a non-collinear antiferromagnetic structure with an intermediate planar arrangement.
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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 DyGa
    (Elsevier, 2015-09-15) Susilo, RA; Cadogan, JM; Muñoz-Pérez, S; Cobas, R; Hutchison, WD; Avdeev, M
    We have used neutron powder diffraction to determine the magnetic structure of DyGa. This compound crystallises in the orthorhombic CrB-type structure with the Cmcm space group (#63) and the magnetic structure comprises ferromagnetic order of the Dy sublattice along the c-axis below TC=115K. Upon cooling below 25K, the Dy magnetic moments cant away from the c-axis towards the a-axis. At 3K, the Dy moment is 9.8(2) μB and the Dy magnetic moments point in the direction θ=22(2)°, ϕ=0° relative to the c-axis. © 2015 Elsevier B.V.
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    Spin-reorientation in DyGa
    (Australian Institute of Physics, 2014-02-05) Susilo, RA; Cadogan, JM; Cobas, R; Muñoz-Pérez, S; Avdeev, M
    The RGa compounds crystallize in the orthorhombic CrB-type structure (Cmcm space-group), which can be viewed as a stacking of trigonal prisms along the crystallographic a-axis with rare earth atoms at the corners and the gallium atoms nearly at the centres. They order ferromagnetically with a Curie temperature ranging from a high of ~187 K in GdGa to a low of 15 K for TmGa. DyGa is a ferromagnet with a Curie temperature (TC) of 115(2) K. Based on single-crystal susceptibility measurements by Shohata, the easy direction of magnetic order was found to be along the c-axis. Recently, Zhang et al. reported a weak shoulder at ~25 K in their magnetization data, which might correspond to a spin-reorientation . In this report, we present our neutron diffraction results to investigate the magnetic ordering of DyGa. Despite the substantial neutron absorption by the Dy (50 at.% of the sample), refinement of our neutron diffraction patterns confirms the c-axis order below TC. Furthermore, upon cooling below 25 K we observe a canting of the Dy moments away from the c-axis towards the a-axis. At 3 K, the Dy moment is 9.8(2) µB and the Dy magnetic moments point in the direction θ = 22(2)° with respect to the crystallographic c-axis.
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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.