https://ogma.newcastle.edu.au/vital/access/ /manager/Index ${session.getAttribute("locale")} 5 https://ogma.newcastle.edu.au/vital/access/ /manager/Repository/uon:42630 Wed 31 Aug 2022 09:04:14 AEST ]]> https://ogma.newcastle.edu.au/vital/access/ /manager/Repository/uon:20853 c, consistent with λeQ²/_s coupling. There is no change in dissipation associated with this high temperature transition, and no evidence in the elastic or anelastic behaviour for any secondary transition at ~920 K, thus supporting the thesis of a single high temperature transformation. Elastic stiffening is observed on cooling through T_N, in accordance with previous studies, and the excess elastic constant appears to scale with the square of the magnetic order parameter. The strains incurred at T_N are a factor of ~20 smaller than those at the structural transition, implying very weak λeQ²/_m coupling and a dominant contribution to the variation in the elastic constants from λeQ²/_m. The increased acoustic dissipation above T_N is consistent with an order–disorder process.]]> Wed 11 Apr 2018 15:07:37 AEST ]]> https://ogma.newcastle.edu.au/vital/access/ /manager/Repository/uon:16627 Wed 11 Apr 2018 10:47:43 AEST ]]> https://ogma.newcastle.edu.au/vital/access/ /manager/Repository/uon:34762 0.957Co_0.043)2As2 by Resonant Ultrasound Spectroscopy as a function of temperature and externally applied magnetic field. Non-linear softening and stiffening of C₆₆ in the stability fields of both the tetragonal and orthorhombic structures has been found to conform quantitatively to the Landau expansion for a pseudoproper ferroelastic transition which is second order in character. The only exception is that the transition occurs at a temperature (TS ≈ 69 K) ~10 K above the temperature at which C66 would extrapolate to zero ( T*_CE59 K). An absence of anomalies associated with antiferromagnetic ordering below TN ≈ 60 K implies that coupling of the magnetic order parameter with shear strain is weak. It is concluded that linear-quadratic coupling between the structural/electronic and antiferromagnetic order parameters is suppressed due to the effects of local heterogeneous strain fields arising from the substitution of Fe by Co. An acoustic loss peak at ~50-55 K is attributed to the influence of mobile ferroelastic twin walls that become pinned by a thermally activated process involving polaronic defects. Softening of C₆₆ by up to ~6% below the normal - superconducting transition at T_C ≈ 13 K demonstrates an effective coupling of the shear strain with the order parameter for the superconducting transition which arises indirectly as a consequence of unfavourable coupling of the superconducting order parameter with the ferroelastic order parameter. Ba(Fe_0.957Co_0.043)₂As₂ is representative of 122 pnictides as forming a class of multiferroic superconductors in which elastic strain relaxations underpin almost all aspects of coupling between the structural, magnetic and superconducting order parameters and of dynamic properties of the transformation microstructures they contain.]]> Tue 03 Sep 2019 18:11:39 AEST ]]> https://ogma.newcastle.edu.au/vital/access/ /manager/Repository/uon:7709 Sat 24 Mar 2018 08:41:37 AEDT ]]> https://ogma.newcastle.edu.au/vital/access/ /manager/Repository/uon:1588 Sat 24 Mar 2018 08:30:31 AEDT ]]> https://ogma.newcastle.edu.au/vital/access/ /manager/Repository/uon:11043 Sat 24 Mar 2018 08:11:46 AEDT ]]> https://ogma.newcastle.edu.au/vital/access/ /manager/Repository/uon:10496 Sat 24 Mar 2018 08:08:58 AEDT ]]> https://ogma.newcastle.edu.au/vital/access/ /manager/Repository/uon:20852 Sat 24 Mar 2018 08:02:54 AEDT ]]> https://ogma.newcastle.edu.au/vital/access/ /manager/Repository/uon:3451 Sat 24 Mar 2018 07:20:32 AEDT ]]> https://ogma.newcastle.edu.au/vital/access/ /manager/Repository/uon:23774 c ≈ 350 K. This matches the evolution of the intensity of the elastic central peak in neutron scattering spectra, and reflects the development of static (or quasistatic) polar nanoregions (PNRs) as if by a mean-field phase transition. Use of a Landau free energy expansion, which includes Γ̅₄ order parameter components to describe ferroelectric contributions and an R¹(+) order parameter to describe cation ordering together with their formal coupling with strain, then allows the pattern of elastic softening expected for a cubic → rhombohedral phase transition to be anticipated. The extent to which observed softening differs from this static mean-field pattern serves to highlight the additional roles of local heterogeneity and relaxation dynamics in determining the relaxor properties of PMN.]]> Sat 24 Mar 2018 07:13:21 AEDT ]]> https://ogma.newcastle.edu.au/vital/access/ /manager/Repository/uon:38136 0.875S. It is concluded that the Besnus transition is a magnetically driven transition characterized by the rotation of the moments out of the crystallographic plane to which they are confined above the transition, accompanied by small atomic displacements that lower the symmetry from monoclinic to triclinic at low temperatures. Based on the phase diagram, magnetically driven phase transitions at low temperatures are predicted in all the commensurate superstructures of pyrrhotite. Based on the phase diagram, magnetically driven spin reorientations at low temperatures are predicted in all the commensurate superstructures of pyrrhotite. The exact nature of the spin rotation is determined by the symmetry of the vacancy-ordered state and based on this spin-flop transitions in 3C and 5C pyrrhotite and a continuous rotation akin to that seen in 4C pyrrhotite are predicted. A Besnus-type transition is also possible in 6C pyrrhotite. Furthermore, it is clarified that 3C and 4C pyrrhotite carry a ferrimagnetic moment whereas 5C and 6C are antiferromagnetic.]]> Fri 06 Aug 2021 16:13:40 AEST ]]>