Browsing by Author "Hutchinson, WD"

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    The 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, SJ
    The 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.
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    Magnetically driven electric polarization in frustrated magnetic oxide multiferroics
    (Australian Institute of Physics, 2014-02-04) Narayanan, N; Reynolds, NM; Li, F; Mulders, AM; Rovillian, P; Ulrich, C; Bartkowiak, M; Hester, JR; McIntyre, GJ; Hutchinson, WD
    In multiferroics more than one ferroic order can coexist and in the present case we are interested in systems which exhibit simultaneous magnetic ordering and electric polarization (EP). Of particular interest are frustrated magnetic materials that exhibit an electric polarization that is strongly coupled to the magnetism [1]. Examples of such multiferroics are RMnO3 (R= Tb, Dy), Ni3V2O8, and RbFe(MoO4)2 [2-4]. This coupling can be utilized in applications such as magnetoelectric random access memory. Although technically relevant, the coupling mechanism between these two orders is complicated [1]. Whereas the magnetic ordering results from exchange interaction of unpaired spins, origins of EP coupled to the magnetic ordering depends on the interplay between lattice, orbital, spin and charge degrees of freedom. Several mechanisms such as the inverse Dzyaloshinskii-Moriya interaction, magnetostriction and coupling of the chirality to the crystal structure or a combination of them are currently discussed depending on the compound [2-5]. Additionally EP has ionic and electronic contributions. In the present work we investigate the coupling of magnetism to EP involving all three above mechanisms, in orthorhombic DyMnO3 (DMO), Cu3Nb2O8 and Ba3NiNb2O9 with neutron powder diffraction (NPD), magnetization and heat capacity measurements focusing on the magnetic and multiferroic phase transitions. In order to investigate the role of the lattice distortion or equivalently the role of oxygen, isotope substitution of 16O with 18O was performed on DMO. All samples are prepared as single phases via the solid state route and NPD experiments are carried out at Wombat and at Echidna at OPAL.
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    Magnetocaloric Mn(Co1-xNix)Ge - structural and magnetic transitions
    (Australian Institute of Physics, 2018-01-30) Ren, QY; Hutchinson, WD; Wang, JL; Studer, AJ; Campbell, SJ
    The structural and magnetic properties of MnCoGe-based alloys have been studied extensively in recent years due to their potential application as magnetic cooling materials based on the magnetocaloric effect (MCE). The Mn(Co1-xNix)Ge series is of particular interest as magnetic transitions in the range 275 K to 345 K generally coincide with a martensitic structural transition TM, with such an overlap then allowing scope for the formation of magneto-structural transitions (ferromagnetic orthorhombic to paramagnetic hexagonal) and hence an associated large MCE [e.g. 1]. Neutron diffraction, magnetisation and x-ray experiments on Mn(Co1-xNix)Ge compounds (x = 0.12 to 1.00) have demonstrated magnetic structures ranging from ferromagnetic for x < 0.50 to non-collinear spiral antiferromagnetic for x > 0.55 at low temperature (e.g. 5 K). TM is found to decrease initially with increasing Ni content and then increase. First-order magneto-structural transitions are observed in Mn(Co1-xNix)Ge samples for ~0.20 < x < ~0.65 with the presence of ferro-/antiferro-magnetic structures in Mn(Co1-xNix)Ge allowing investigation of both direct and inverse magnetocaloric effects. Our results (including the magnetic phase diagram for Mn(Co1-xNix)Ge) are discussed in terms of the increase of valence electron concentration on substitution of Ni (3d84s2) for Co (3d74s2) in the orthorhombic phase, leading to expansion of the unit cell and redistribution of the valence electrons [2].
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    Negative thermal expansion of Ni-doped MnCoGe around room temperature - magnetic tuning
    (Australian Institute of Physics, 2019-02-05) Ren, QY; Hutchinson, WD; Wang, JL; Studer, AJ; Wang, G; Zhou, H; Ma, J; Campbell, SJ
    Several materials have been shown to exhibit abnormal contraction with increasing temperature; the phenomenon of negative thermal expansion (NTE). Given this special property, NTE materials fulfill important functions in many modern technologies, such as electrodes of fuel cell, organic light-emitting diode (OLED), optical fibre, as well as high precision electronics and optical mirrors. In general, Nate properties are associated with local structural distortions or phase transitions, such as transverse phonon vibration in rigid unit modes, exile network of metal-organic framework, charge transfer, magneto-volume effect, ferroelectric transition, as well as displacive phase transition. Control or manipulation of Nate properties have become topics of increasing importance over the past two decades. Effective methods to produce materials with Nate properties include chemical doping, nanostructuralization, hydration and applied pressure. Recently, MoCoGe-based compounds were considered as a group of materials that exhibit giant NTE, with this behaviour attributed to the displacive martensitic phase transformation. In this investigation, we reported a new method to manipulate the NTE properties using applied magnetic fields. It is found that doping of 5% Ni on the Mn site could bring about a magneto-structural (MS) coupling in MnCoGe-based compounds. Magnetic-field-dependent neutron diffraction measurements demonstrated that an 8 T magnetic field could suppress the NTE by 31% at 295 K through this MS coupling.
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    Resonant x-ray diffraction and the observation of strange quantities
    (Australian Institute of Physics, 2012-02-02) Princep, AJ; Mulders, AM; Schierle, E; Weschke, E; Hester, JR; Hutchinson, WD; Tanaka, Y; Terada, N; Narumi, Y; Staub, U; Scagnoli, V; Nakamura, T; Kikkawa, A; Lovesey, SW; Balcar, E
    Condensed matter physics has a growing reputation for providing an opportunity to observe exotic particles and states of matter that have an analogue in other areas of physics. Examples of this include the observation of Dirac strings and magnetic monopoles in spin-ice materials [1], spinon / holon separation in gated nanowires [2], and toroidal moments (anapoles) in the ubiquitous cuprates [3]. Resonant X-ray Diffraction (RXD) is well suited to the observation of a variety of quantities that behave differently under time reversal, coordinate inversion, and rotation [4]. It is possible to distinguish between competing orders and we have determined the orbital order in RB2C2, including higer order terms (as illustrated on the cover page) [5,6]