arXiv subjects

Andrew J. Studer

Publications and source records attributed to Andrew J. Studer.

5 recordsLinked to original sources

arXiv2025

Wombat, the high intensity diffractometer in operation at the Australian Centre for Neutron Scattering

Wombat is the high intensity neutron diffractometer in operation at the Australian Centre for Neutron Scattering. While primarily used as a high-speed powder diffractometer, the high-performance area detector allows both texture characterisation and single-crystal measurements. The instrument can be configured over a large range of operational parameters, which are characterised in this contribution to aid experimental planning. Wombat is particularly optimised for the study of materials in situ and in operando using the wide range of sample environment available at the centre. Over 17 years of operation, Wombat has been used to explore a broad range of materials, including: novel hydrogen-storage materials, negative-thermal-expansion materials, cryogenic minerals, piezoelectrics, high performance battery anodes and cathodes, high strength alloys, multiferroics, superconductors and novel magnetic materials. This paper will highlight the capacity of the instrument, recent comprehensive characterisation measurements, and how the instrument has been utilised by our user community to date.

physics.ins-det↗

arXiv2022

High-resolution diffraction reveals magnetoelastic coupling and coherent phase separation in tetragonal CuMnAs

Tetragonal CuMnAs was the first antiferromagnet where reorientation of the Néel vector was reported to occur by an inverse spin galvanic effect. A complicating factor in the formation of phase-pure tetragonal CuMnAs is the formation of an orthorhombic phase with nearly the same stoichiometry. Pure-phase tetragonal CuMnAs has been reported to require an excess of Cu to maintain a single phase in traditional solid state synthesis reactions. Here we show that subtle differences in diffraction patterns signal pervasive inhomogeneity and phase separation, even in Cu-rich Cu$_{1.18}$Mn$_{0.82}$As. From calorimetry and magnetometry measurements, we identify two transitions corresponding to the Néel temperature (T$_N$) and an antiferromagnet to weak ferromagnet transition in Cu$_{1.18}$Mn$_{0.82}$As and CuMn$_{0.964}$As$_{1.036}$. These transitions have clear crystallographic signatures, directly observable in the lattice parameters upon in-situ heating and cooling. The immiscibility and phase separation could arise from a spinoidal decomposition that occurs at high temperatures, and the presence of a ferromagnetic transition near room temperature warrants further investigation of its effect on the electrical switching behavior.

cond-mat.mtrl-sci↗

arXiv2018

Spin Dynamics and Magnetoelectric Coupling Mechanism of Co4Nb2O9

Neutron powder diffraction experiments reveal that Co4Nb2O9 forms a noncollinear in-plane magnetic structure with Co2+ moments lying in the ab plane. The spin-wave excitations of this magnet were measured by using inelastic neutron scattering and soundly simulated by a dynamic model involving nearest and next-nearest neighbour exchange interactions, in-plane anisotropy and the Dzyaloshinskii-Moriya interaction. The in-plane magnetic structure of Co4Nb2O9 is attributed to the large in-plane anisotropy while the noncollinearity of the spin configuration is attributed to the Dzyaloshinskii-Moriya interaction. The high magnetoelectric coupling effect of Co4Nb2O9 in fields can be explained by its special in-plane magnetic structure.

cond-mat.mtrl-sci↗

arXiv2011

Spin-gap opening accompanied by a strong magnetoelastic response in the S=1 magnetic dimer system Ba3BiRu2O9

Neutron diffraction, magnetization, resistivity, and heat capacity measurements on the 6H-perovskite Ba3BiRu2O9 reveal simultaneous magnetic and structural dimerization driven by strong magnetoelastic coupling. An isostructural but strongly displacive first-order transition on cooling through T*=176 K is associated with a change in the nature of direct Ru-Ru bonds within Ru2O9 face-sharing octahedra. Above T*, Ba3BiRu2O9 is an S=1 magnetic dimer system with intradimer exchange interactions J0/kB=320 K and interdimer exchange interactions J'/kB=-160 K. Below T*, a spin-gapped state emerges with Δ\approx220 K. Ab initio calculations confirm antiferromagnetic exchange within dimers, but the transition is not accompanied by long range-magnetic order.

cond-mat.str-el↗

arXiv2009

Structural phase transition in TmxFe1-xSe0.85 (Tm = Mn and Cu) and its relation to superconductivity

In this letter, we report the results of detailed studies on Mn- and Cu-substitution to Fe-site of beta-FeSe, namely MnxFe1-xSe0.85 and CuxFe1-xSe0.85. The results show that with only 10 at% Cu-doping the compound becomes a Mott insulator. Detailed temperature dependent structural analyses of these Mn- and Cu-substituted compounds show that the structural transition, which is associated with the changes in the building block FeSe4 tetrahedron, is essential to the occurrence of superconductivity in beta-FeSe.

cond-mat.supr-con↗