Browsing by Author "Cobas, R"
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- ItemThe effect of Fe and Ni substitution in magnetocaloric MnCoGe(Australian Institute of Physics, 2013-02-05) Ren, QY; Hutchinson, WD; Wang, JL; Kemp, W; Cobas, R; Cadogan, JM; Campbell, SJThe MnCoGe family of compounds shows potential as a rare-earth free material for magnetocaloric applications around room temperature. We present initial findings on the effects of the substitution of Fe and Ni for Mn in a series of Mn1-xTxCoGe compounds (T = Fe, Ni; x = 0.04 - 0.10). Investigations include x-ray diffraction, differential scanning calorimetry(200 - 670 K) and magnetisation (5 - 350 K) measurements in magnetic fields up to 8 T. The influence of the Fe and Ni substitutions on the transformation temperature between the hexagonal and orthorhombic structures, the resultant phase fractions and their magnetic phase transitions are reported.
- ItemMagnetic order and spin-reorientation in HoGa(IOP Publishing, 2012-01-01) Susilo, RA; Muñoz-Pérez, S; Cobas, R; Cadogan, JM; Avdeev, MWe 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
- ItemMagnetic 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, MNot available
- ItemMagnetic order and structural properties of Tb2Fe2Si2C(Elsevier, 2016-01-05) Susilo, RA; Cadogan, JM; Hutchison, WD; Avdeev, M; Cobas, R; Muñoz-Pérez, S; Campbell, SJThe 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.
- ItemMagnetic ordering in Ho2Fe2Si2C(American Institute of Physics, 2015-02-23) Susilo, RA; Cadogan, JM; Cobas, R; Hutchison, WD; Avdeev, M; Campbell, SJWe 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.
- ItemMagnetic ordering in TmGa(IOP Science, 2014-03-03) Cadogan, JM; Stewart, GA; Muñoz-Pérez, S; Cobas, R; Hansen, BR; Avdeev, M; Hutchison, WDWe have determined the magnetic structure of the intermetallic compound TmGa by high-resolution neutron powder diffraction and 169Tm Mössbauer spectroscopy. This compound crystallizes in the orthorhombic (Cmcm) CrB-type structure and its magnetic structure is characterized by magnetic order of the Tm sublattice along the a-axis. The initial magnetic ordering occurs at 15(1) K and yields an incommensurate antiferromagnetic structure described by the propagation vector k1 = [0 0.275(2) 0]. At 12 K the dominant ferromagnetic ordering of the Tm sublattice along the a-axis develops in what appears to be a first-order transition. At 3 K the magnetic structure of TmGa is predominantly ferromagnetic but a weakened incommensurate component remains. The ferromagnetic Tm moment reaches 6.7(2) μB at 3 K and the amplitude of the remaining incommensurate component is 2.7(4) μB. The 169Tm hyperfine magnetic field at 5 K is 631(1) T. © Copyright IOP Publishing
- ItemSpin-reorientation in DyGa(Elsevier, 2015-09-15) Susilo, RA; Cadogan, JM; Muñoz-Pérez, S; Cobas, R; Hutchison, WD; Avdeev, MWe 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.
- ItemSpin-reorientation in DyGa(Australian Institute of Physics, 2014-02-05) Susilo, RA; Cadogan, JM; Cobas, R; Muñoz-Pérez, S; Avdeev, MThe 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.