Browsing by Author "Goossens, DJ"
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- ItemAn AC susceptibility study of strontium cobaltates, Ln1-xSrxCoO3-δ where Ln = Y, Ho and Dy(Australian Institute of Physics, 2003-02-04) Wilson, KF; Goossens, DJ; Cochrane, JM; James, MWe discuss the AC susceptibility of members of the Ln1-xSrxCoO3-δ family of materials where 0.66 ≤ x ≤ 0.9 and Ln = Y, Dy and Ho. The materials exhibit ferro- or ferrimagnetic ordering below room temperature. Despite the disorder introduced by mixed Co valence states, no glassiness is apparent in the imaginary part of the AC susceptibility or in the frequency dependence of the transition temperature. In addition, in the Dy and Ho materials it is found that the rare earth moments do not couple to the Co magnetic lattice.
- ItemThe antiferromagnetic structure of BaPrO3(Australian Institute of Physics, 2004-02-04) Robinson, RA; Goossens, DJ; Telling, MFIn this study, we report the magnetic space group and moment direction in the canted antiferromagnetic system BaPrO3. While previous work had shown that perovskite-based BaPrO3, which is orthorhombic crystallographically, orders antiferromagnetically below 11.7K, and that it also exhibits weak ferromagnetism at the same temperatures, the exact magnetic symmetry and moment directions were previously undetermined. In this report, we show, by means of cold-neutron high-resolution powder diffraction, that the magnetic (Shubnikov) group is in fact Pb’n’m, and that the antiferromagnetism lies along the a-axis, with μx = 0.37±0.03 μB. This is qualitatively and quantitatively consistent with previous neutron diffraction results reporting the configurational symmetry of the antiferromagnetism. Our model explicitly allows for ferromagnetism, and necessarily implies that the ferromagnetism previously observed in bulk magnetisation measurements must lie along the z-axis. We discuss ways in which this prediction might be tested, even in the absence of single crystals of BaPrO3.
- ItemCoupled Li1+/Nb5+ and O2-/F- ordering on the Na and Cl sites of the average NaCl structure of Li4NbO4F(Elsevier, 2009-05) Norén, L; Withers, RL; Goossens, DJ; Elcombe, MM; Kearley, GJThe average, as well as the cation and anion 'disordered', crystal Structure of Li4NbO4F has been carefully investigated via coupled neutron and X-ray powder diffraction studies as well as via electron diffraction studies. The existence of a spectacular highly structured diffuse intensity distribution in the latter provides strong evidence for coupled Li1+/Nb5+ and O2-/F- ordering on the Na and Cl sites of the average NaCl structure of Li4NbO4F. Bond valence sum calculations have been used to investigate local crystal chemistry as well as to Suggest plausible local crystal chemical constraints while ab initio DFT based theoretical calculations of a 2 x 2 x 2 supercell have been carried Out in order to provide additional insight into the local crystal chemistry of this compound. © 2009, Elsevier Ltd.
- ItemCrystal and magnetic structure of (1-x)BiFeO3-xSrTiO3 (x=0.2, 0.3, 0.4 and 0.8)(Elsevier, 2013-11-01) Goossens, DJ; Weekes, CJ; Avdeev, M; Hutchison, WDThe effect of doping SrTiO3 into BiFeO3 on the magnetic and crystal structure has been explored using powder neutron diffraction for (1−x)BiFeO3–xSrTiO3(1−x)BiFeO3–xSrTiO3 where x=0.2, 0.3, 0.4, 0.6 and 0.8. While the data are not sensitive to the cycloidal component of the magnetic ordering, the evolution of the collinear antiferromagnetic moment of the G-type antiferromagnetic component with T and x has been explored, as have structural parameters. It is found that for x≤0.4x≤0.4 pure phase samples form in the R3c cell, and for x =0.8 a non-magnetic Pm3¯m phase is obtained. The x=0.6 sample gives a mixed phase. Through the R3c phase the magnetic structure does not change appreciably apart from the reduction of magnetic moment magnitude with the increasing T and/or x. © 2013, Elsevier Inc.
- ItemCrystal and magnetic structures in perovskite-related La1-xCaxFeO3-δ (x=0.2, 0.33)(Elsevier, 2011-12) Hudspeth, JM; Stewart, GA; Studer, AJ; Goossens, DJUsing sol gel synthesis, single phase perovskite-related compounds in the family La1-xCaxFeO3-δ have been formed for x=0.2 and x=0.33, but not for x=0.5. The x=0.2 and x=0.33 compounds are isostructural with LaFeO3 (Pnma). The magnetic structure of La 0.8 Ca0.2FeO3-δ has been studied through Mössbauer spectroscopy and neutron powder diffraction. La 0.8 Ca 0.2FeO3-δ is a G-type antiferromagnet with a magnetic moment magnitude of 3.0±0.2μB at room temperature. The reduction in the magnitude of the antiferromagnetic moment compared to that published for LaFeO3 is explained by the measurement being taken at room temperature rather than 4 K and by the presence of Fe4 ions which have weaker exchange interactions than Fe3, causing a strong reduction in TN. Room temperature Mössbauer shows a broad magnetic hyperfine field distribution on the Fe sites in both La0.8 Ca0.2FeO3-δ and La0.67 Ca 0.33FeO3-δ. On cooling, disproportionation of Fe14 into Fe3 and Fe5 is apparent, and the resulting Fe5 sextet measured at low temperature gives a reliable measure of the Fe4 fraction. This in turn shows that creation of high-oxidation-state Fe is the dominant charge balance mechanism on doping Ca2 into the Ln3 site indicating a disordered distribution of Fe3 and Fe4. The lack of broadening of the Fe 5 sextet suggests that there may be ordering in the distribution of Fe5. © 2011 Elsevier Ltd.
- ItemThe crystal and magnetic structures of LaCa2Fe3-xMxO8 (M=Al, Ga, In)(Elsevier, 2012-06-27) Goossens, DJ; Henderson, LSF; Trevena, S; Hudspeth, JM; Avdeev, M; Hester, JRLaCa2Fe3O8 (A3B3O8) is an example of a layered structure in that it consists of pairs of octahedral, perovskite-like layers alternating with a single tetrahedral layer. This work explores the doping of non-magnetic group 13 elements, M=Al, Ga and In, onto the B-site of LaCa2Fe3−xMxO8 as a function of x. The structural and magnetic effects are examined using a combination of neutron and X-ray diffraction. Solubility limits are established. It is found that for M=Ga the solubility limit occurs between x=1.0 and x=1.25, for the synthesis conditions used, while there is evidence for low ( x < 0.25 ) but non-zero substitution of Al. Structural refinements at x=1 suggest that Ga prefers neither the tetrahedral nor octahedral sites. The magnetic structure of LaCa2Fe2GaO8 has been examined using neutron diffraction at 3.2 K and room temperature. At low temperature the staggered moment per Fe3+ is 3.8 ( 1 ) μ B in LaCa2Fe3O8 and 4.8 ( 1 ) μ B in LaCa2Fe2GaO8. The magnetic space group (P2b21′ma′) and moment direction (along c) does not appear to change with Ga substitution. © 2012, Elsevier Ltd.
- ItemThe crystal and magnetic structures of LaCa2Fe3O8 and NdCa2Fe3O8(Institute of Physics, 2009-03-25) Hudspeth, JM; Goossens, DJ; Studer, AJ; Withers, RL; Norén, LThe crystal and magnetic structures of LaCa2Fe3O8 and NdCa2Fe3O8 have been established using a combination of x-ray, neutron and electron diffraction. It was already considered likely that LaCa2Fe3O8 and NdCa2Fe3O8 were made up of stacked perovskite-like layers of FeO6 octahedra, with every third layer being replaced by a layer of tetrahedrally coordinated Fe, rather like a variation on the Brownmillerite (Ca2Fe2O5) structure type. We have gone further and determined a likely space group for this Grenier phase and determined the magnetic structure of the compounds at room temperature. The space group is found to be P2(1)ma (b axis as the long axis), and the crystal structure has been refined, subject to the stacking faulting along the long axis that is apparent in electron diffraction patterns. The magnetic structure of LaCa2Fe3O8 is shown to consist of antiferromagnetically ordered Fe3+ ions on a collinear G-type antiferromagnetic structure, with the magnetic moments most likely (anti) parallel with the c axis, and of magnitude 3.4 +/- 0.2 mu(B) (3.6 +/- 0.2 mu(B) for NdCa2Fe3O8). The result is reasonable given the magnetic structures of the end members of the La1-xCaxFeO3 series, LaFeO3 (x = 0) and Ca2Fe2O5 (x = 1). © 2009, Institute of Physics
- ItemEvolution with applied field of the magnetic structure of TbNiAl4(Springer Link, 2014-12-17) White, R; Hutchison, WD; Goossens, DJ; Studer, AJ; Nishimura, KNeutron powder diffraction data of TbNiAl4 has been re-examined using a representational analysis, allowing a new model of the magnetic structure to be deduced. The basis vectors obtained describe an ‘elliptical helix’ type structure in which the moments rotate in the ab-plane as one moves along the c-axis. This new model has been used to simulate the expected result of a Low Temperature Nuclear Orientation (LTNO) experiment involving 299 keV gamma-ray emission from the 160Dy daughter of aligned 160Tb nuclei. Results of the simulation along the a-axis appear to partly match currently existing experimental data, with good agreement in the magnitude of lost anisotropy. © 2014, Springer International Publishing.
- ItemField-induced incommensurate spin structure of TbNiAl4(American Physical Society, 2012-07-13) Hutchison, WD; Goossens, DJ; Whitfield, RE; Studer, AJ; Nishimura, K; Mizushima, TTbNiAl(4) exhibits incommensurate and commensurate magnetic ordering as a function of temperature. As a function of applied field it undergoes a series of magnetic phase transitions. The first of these transitions, into an intermediate spin arrangement, is the source of a large inverse magnetocaloric effect, an unusual result given that an aligning field is being applied. This has potential uses in magnetic cooling. Here, single-crystal neutron diffraction with applied magnetic field is used to obtain the intermediate field spin arrangement in TbNiAl(4). We find that not only does the applied field drive the system from commensurate to incommensurate ordering, but that the phase transition shows hysteresis such that a mixed state simultaneously showing commensurate and incommensurate antiferromagnetic ordering, along with ferromagnetism, can be obtained. © 2012, American Physical Society.
- ItemInvestigating short-range order in triglycine sulphate using x-ray and neutron diffuse scattering(Australian Institute of Physics, 2012-02-02) Hudspeth, JM; Goossens, DJ; Gutmann, MJ; Studer, AJ; Welberry, TRTriglycine sulphate (TGS) [(NH2CH2COOH)3H2SO4] is a hydrogen-bonded ferroelectric with a phase transition temperature of 322K . The phase transition is reversible and second order, order disorder type, making TGS of fundamental interest in the field of phase transitions . Above the critical temperature, one of the glycine molecules is disordered across a mirror plane. Below the critical temperature, it chooses a side, breaking the symmetry. The ferroelectric state is obtained through the ordering of the glycine orientations on neighbouring sites, but the mechanism for the phase transition is not well understood. We have investigated the short-range order in TGS by collecting single crystal x-ray and neutron diffuse scattering data on hydrogenous and fully deuterated TGS respectively. Data was collected at temperatures from well below to well above TC. We have also developed a model for the short-range order using the program ZMC . This has given us some new insight into the behavior of the disordered glycine in TGS. For example, above TC, the orientations of the disordered glycine appear to be correlated over short range rather than being completely random as suggested by the average structure.
- ItemMagnetic order studies of ErNiAl4(Australian Institute of Physics, 2007-02-06) Hutchison, WD; Goossens, DJ; Saensunon, B; Stewart, GA; Avdeev, M; Nishimura, KSpecific heat measurements on ErNiAl4 show a phase transition at 5.8(1) K. Magnetisation data confirms the low temperature phase is antiferromagnetic in nature, while neutron powder diffraction data suggests an incommensurate structure similar to the intermediate magnetic phase of TbNiAl4.
- ItemMagnetic properties of Dy 1-x Sr x CoO 3-δ (x = 0.67 to 0.95)(Australian Institute of Physics, 2021-02-04) Goossens, DJ; Wilson, KF; James, MThe AC magnetic susceptibility of Dy1-xSrxCoO3-δ has been measured from 17 to 320 K for a range of samples, x = 0.67 to 0.95. These results have shown that for x = 0.95 the systems enters a spinglass state at approximately 131K on cooling. This is demonstrated by a large cusp in the imaginary susceptibility, indicating the onset of time-dependent effects. For smaller x, the system enters a magnetically ordered state at approximately 300K. This state shows evidence for a spin state transition in the Co ions at around 120K , but no evidence of a spin-glass phase. Structurally, the system is tetragonal, I4/mmm, becoming closer to cubic as x increases, until at x = 0.95 the system is metrically cubic. Further, as x increases the fraction of Co4+ in the system also increases, as shown by TGA. At x = 0.95 over 50% of the Co sites are 4+, and the mixture of exchange interactions resulting is thought to give rise to the spinglass state. At smaller x the system appears weakly ferromagnetic, probably due to local ferromagnetic clusters , with the Dy moments remaining paramagnetic to temperatures below the instrumental limit.
- ItemMagnetic properties of Gd 1-x Sr x CoO 3-δ (x = 067, 090 and 095)(Australian Institute of Physics, 2005-01-31) Wilson, KF; Goossens, DJ; James, MLanthanide cobaltates (Ln1-xSrxCoO3-δ) (Ln = lanthanide ion) with perovskite-derived structures are of potential use in solid oxide fuel cells [1-4] and oxygen separation [5-6]. The materials show magnetic glassiness [7-8] and ferromagnetism . La1-xSrxCoO3-δ has been widely studied [10 for example]. Interest has recently increased in phases with the smaller lanthanide ions such as Ho, Y and Dy . This work adds to a systematic exploration of the structure and magnetic properties of this family of materials. The physical properties of these materials depend on composition (Ln3+/Sr2+, O/vacancy, Co3+/Co4+). Oxygen ionic conductivity changes with the O/vacancy ordering and associated structural relaxation ; magnetic behaviour will be affected by the Co3+/Co4+ ratio and distribution.
- ItemMagnetic structure and glassiness in Fe0.5Ni0.5PS3(Elsevier, 2013-05-01) Goossens, DJ; Brazier-Hollins, S; James, DR; Hutchison, WD; Hester, JRThis work explores the magnetic properties of Fe0.5Ni0.5PS3. The system shows pronounced hysteresis in the magnetic phase transition temperature as a function of the direction of the change in temperature. Field cooled/zero field cooled hysteresis is not pronounced. However, the transition temperature between antiferromagnetic and paramagnetic order occurs at approximately 97 K on cooling, but at 138 K on warming, whether the warming is after zero field or field cooling. This is indicative of magnetic glassiness, and made all the more unusual because all measurements exhibit a transition to a third magnetic phase existing at temperatures below to 14 K . The intermediate phase relaxes on a laboratory time scale of the order of 48 min, into an antiferromagnetic state whose magnetic structure is, from neutron diffraction, indistinguishable from the low temperature state. This low temperature state shows magnetic ordering consistent with that observed in CoPS3 and NiPS3. Analysis of the neutron measurements shows that the direction of moments cannot be along the b-axis. It is also shown that the moments are unlikely to lie in the c* direction. Therefore, we suggest that the moments lie along the a-axis.© 2013, Elsevier Inc.
- ItemMicrostructure of horseshoe nails using neutron diffraction.(Springer, 2009-07-02) Goossens, DJ; Studer, AJ; Stachurski, ZHNeutron diffraction allows nondestructive testing of the bulk microstructure of mechanical components. The microstructures of horseshoe nails made through three different processes have been explored as a function of position along the nail. Despite all nails being made of similar plain low-carbon steel and being process annealed after manufacture, the microstructures are far from the same. Nails made from strip, using a cold forging stamping process, show narrower diffraction peaks indicating a narrower distribution of lattice parameters and also show diffraction peak intensity ratios closer to those expected for unstrained steel. Thus, the distribution of the orientation of grains in these nails is closer to that of undistorted steel compared to nails made through the other two processes considered—one a drawing from wire and the other a combination of rolling and cold forging. The blades of the drawn nails showed little preferred orientation but the converse was true in the heads. Differing patterns of preferred orientation suggest that the various manufacturing approaches result in substantially different mechanical advantages for the three types of nails, a result in accord with mechanical testing. © 2010, Springer.
- ItemA neutron diffraction study of the phase transition of fully deuterated triglycine sulphate (ND2CD2COOD)(3 center dot) D2SO4(Wiley-V CH Verlag GMBH., 2013-03-01) Hudspeth, JM; Goossens, DJ; Gutmann, MJ; Studer, AJUsing neutron single crystal and powder diffraction, the first thorough investigation of the structure of fully deuterated triglycine sulphate, (ND2CD2COOD)3.D2SO4 is presented, including its evolution with T, through its structural phase transition. This includes new precise structural parameters determined at several key temperatures above and below TC using single crystal diffraction, and for the first time a parametric study has been undertaken over a wide temperature range — from 4 to 500 K in 2 K steps. It was found that fully deuterated TGS shows a structure consistent with hydrogenous TGS and partially deuterated TGS. The evolution of several key hydrogen bond lengths suggests that weakening of the H-bond network with T is crucial in decoupling the polarising glycine molecules from the other glycines and allowing the long-range ferroelectric order to break down. A new parameterisation of the phase transition is demonstrated. Contrary to results of physical properties measurements, there is no evidence of a second low temperature phase transition in TGS – no low temperature anomalies were observed in the crystal structure. © 2013, Wiley-VCH Verlag.
- ItemNeutron diffuse scattering in deuterated para-terphenyl, C18D14(Institute of Physics, 2009-03-25) Goossens, DJ; Beasley, AG; Welberry, TR; Gutmann, MJ; Piltz, RONeutron diffuse scattering is used to explore the short-range order (SRO) in deuterated para-terphenyl, C18D14. The crystal shows SRO because the central of the three phenyl groups of each molecule can twist positively or negatively and these twists are correlated over the local scale. The presence of incipient Bragg peaks at (1/2 1/2 0) at 200 K shows that these flips are negatively correlated along the a direction (nearest neighbour correlation coefficient of similar to-0.3) and b direction (nearest neighbour correlation coefficient of similar to-0.87) and appear essentially uncorrelated along c. Diffuse peak anisotropy indicates that the range of the correlations along b is found to be similar to 3 times that along a. These correlations persist, although weaker, at room temperature. A Monte Carlo simulation was used to impose a correlation structure on the population of central ring twists that was deduced from Bragg scattering. By then allowing displacive relaxation of the structure, the observed diffuse scattering was well reproduced. Modelling the displacive motions of molecules showed that the positions of nearest ab-plane neighbour molecules are strongly positively correlated, particularly for motions approximately parallel to a, while the displacive correlations are weaker between molecules stacked along c. The apparent contradiction that the displacements are most strongly correlated along a while the occupancies are most strongly correlated along b is explained in terms of the connectivity of molecular interactions. © 2009, Institute of Physics
- ItemA polarised neutron study of crystal field transitions in CeCu6(Australian Institute of Physics, 2004-02-04) Harker, SJ; Hicks, TJ; Goossens, DJ; Mulders, AM; Fied, Y; Yu, DH; Kennedy, SJCeCu6 is a heavy Fermion compound in which the Ce magnetic moment is suppressed by the Kondo effect resulting from the admixture of the local 4f electrons with the conduction electrons. Crystal field transitions between the low-lying states of the Ce ion have been observed using inelastic neutron scattering [1–3]. The transitions were contaminated by phonon scattering which can be corrected using a complex scaling function using a complementary spectrum of LaCu6. Neutron time of flight spectroscopy with neutron polarisation analysis permits the in situ separation of magnetic and lattice vibrational energy spectra. Preliminary experiments on LONGPOL allow an indicative separation of a broadened crystal field transition and features due to lattice vibrations . The preliminary analysis indicated an inelastic spin-flip feature at -12 meV which is due to the crystal field while an inelastic non-spin-flip feature at -6 meV is predominantly due to phonon scattering. A more complete polarisation analysis study has been performed using a magnetic coil to switch the polarisation at the sample position between perpendicular and parallel to the scattering vector. These results and their interpretation are reported here.
- ItemA quantum multi-critical point in CeCu6−xAux(Elsevier B. V., 2006-11-15) Robinson, RA; Goossens, DJ; Torikachvili, MS; Kakurai, K; Okumura, HCeCu6−xAux is a well-known heavy-fermion system in which the ground state is antiferromagnetically ordered for x>0.1 and temperatures below 1 K. Non-Fermi liquid behaviour occurs around this critical concentration. The parent compound, CeCu6, exhibits a structural phase transition near 230 K, where it changes from the Pnma orthorhombic room-temperature structure to the P21/c monoclinic structure. The monoclinicity increases as temperature falls, with β reaching 91.44° at 10 K. In the work presented here, powder neutron diffraction is used to explore the monoclinicity at 8 K as a function of composition for 0.00.1, indicates that long-range order disappears at exactly the same critical concentration. At a minimum, the structural distortion and antiferromagnetism seem to be competing with each other, and this raises the intriguing possibility that lattice degrees of freedom are important in the non-Fermi liquid regime.
- ItemStructure and magnetism in rare earth strontium-doped cobaltates(Elsevier, 2006-11-15) James, M; Morales, L; Wallwork, KS; Avdeev, M; Withers, RL; Goossens, DJSubstantial interest has recently been generated by rare earth cobaltate compounds as cathode materials for solid oxide fuel cells. We have synthesised a wide range of single–phase perovskite-based rare earth cobaltates (Ln1−xSrxCoO3−δ) (Ln=La3+–Yb3+). A combination of electron and X-ray diffraction of these phases reveals a complex family of tetragonal and orthorhombic superstructures. The nature of structural and magnetic ordering relies on both cation and oxygen vacancy distribution. Phase boundaries exists between compounds containing large, medium and small rare earths (between Nd3+ and Sm3+, and also between Gd3+ and Dy3+) and also at different Sr-doping levels. Powder neutron diffraction has been used in conjunction with the other techniques to reveal cation and oxygen vacancy ordering within these materials. These phases show mixed valence (3+/4+) cobalt oxidation states that increases with Sr content. A range of magnetic behaviours has been observed, including ordered antiferromagnetism at elevated temperatures (>300 K) in Ho0.2Sr0.8CoO2.75. © 2006 Elsevier B.V.