Using applied field, pressure, and light to control magnetic states of materials

Due to their low energy scales, flexible architectures, and unique exchange pathways, molecule-based multiferroics host a number of unique properties and phase transitions under external stimuli. In this dissertation, we reveal the magnetic- and pressure-driven transitions in [(CH3)2NH2]Mn(HCOO)3 and (NH4)2[FeCl5(H2O)], present a detailed investigation of these materials away from standard equilibrium phases, and develop rich two- and three-dimensional phase diagrams. The first platform for exploring phase transitions is [(CH3)2NH2]Mn(HCOO)3. This type-I multiferroic contains Mn centers linked by formate ligands creating Mn-O-C-O-Mn superexchange pathways. Magnetization measurements reveal two transitions - a spin-flop and a transition to the fully polarized state - and the loss of long-range order above the Neel temperature. Extending to the high-pressure regime, we perform vibrational spectroscopy across the order-disorder transition and use a correlation group analysis to determine the high pressure space groups. The superexchange pathway plays a crucial role in triggering the structural crossover to lower symmetry. Despite having driving different space groups above/below the order-disorder temperature, compression lowers each symmetry to the polar space group P1. We develop the pressure - temperature - magnetic field phase diagram for [(CH3)2NH2]Mn(HCOO)3 and articulate the potential for enhanced polarization under compression. The type-II multiferrroic (NH4)2[FeCl5(H2O)] is different. It hosts a unique set of exchange pathways mediated by through-space hydrogen- and halogen-bonding. Magnetization displays a series of transitions, including the spin-flop, transition to the fully saturated state, and many associated reorientation transitions. Extending to high-pressure studies, we employ infrared absorption and Raman scattering under compression to reveal an increase in hydrogen bonding and changes in the FeCl5H2O polyhedron that are unique to this regime. A space group analysis uncovers a sequence of space group changes that suggests it is driven to a polar space group. We generate the complete three-dimensional phase diagram, which displays the many competing structural and magnetic interactions. Together, these findings uncover magnetically-driven quantum phase transitions and reduced symmetry under compression to likely polar space groups. This work motivates extended investigations of non-equilibrium phases under external stimuli in these and other molecule-based materials with low energy scales, flexible architectures and unique spin interactions

High-pressure spectroscopic investigation of multiferroic Ni3TeO6

We combined diamond anvil cell techniques, infrared and Raman spectroscopies, and lattice dynamics calculations to explore the high pressure properties of multiferroic Ni3TeO6. Using a frequency trend analysis, we trace a subtle decrease in compressibility near 4 GPa to a minimum in the O-Ni2-O bond angle. This unique behavior emanates from the proximity of the Ni2 center in the Ni3-Ni2-Ni1-Te chain to a flexible pocket that is intrinsic to the crystal structure. At the same time, predicted trends in the superexchange pathways are consistent with greater antiferromagnetic character under compression, in line with both phase stability calculations and direct susceptibility measurements. These findings highlight opportunities for local structure control of corundumlike materials

Reducing the environmental impact of surgery on a global scale: systematic review and co-prioritization with healthcare workers in 132 countries

Abstract Background Healthcare cannot achieve net-zero carbon without addressing operating theatres. The aim of this study was to prioritize feasible interventions to reduce the environmental impact of operating theatres. Methods This study adopted a four-phase Delphi consensus co-prioritization methodology. In phase 1, a systematic review of published interventions and global consultation of perioperative healthcare professionals were used to longlist interventions. In phase 2, iterative thematic analysis consolidated comparable interventions into a shortlist. In phase 3, the shortlist was co-prioritized based on patient and clinician views on acceptability, feasibility, and safety. In phase 4, ranked lists of interventions were presented by their relevance to high-income countries and low–middle-income countries. Results In phase 1, 43 interventions were identified, which had low uptake in practice according to 3042 professionals globally. In phase 2, a shortlist of 15 intervention domains was generated. In phase 3, interventions were deemed acceptable for more than 90 per cent of patients except for reducing general anaesthesia (84 per cent) and re-sterilization of ‘single-use’ consumables (86 per cent). In phase 4, the top three shortlisted interventions for high-income countries were: introducing recycling; reducing use of anaesthetic gases; and appropriate clinical waste processing. In phase 4, the top three shortlisted interventions for low–middle-income countries were: introducing reusable surgical devices; reducing use of consumables; and reducing the use of general anaesthesia. Conclusion This is a step toward environmentally sustainable operating environments with actionable interventions applicable to both high– and low–middle–income countries

Symmetry progression and possible polar metallicity in NiPS3 under pressure

van der Waals solids are ideal platforms for the discovery of new states of matter and emergent properties under external stimuli. Under pressure, complex chalcogenides like MPS3 (M = Mn, Ni, Co, V) host sliding and structural transitions, insulator-to-metal transitions, the possibility of an orbitally-selective Mott state, piezochromism, and superconductivity. In this work, we bring together diamond anvil cell techniques, infrared and Raman scattering spectroscopies, and X-ray diffraction with a detailed symmetry analysis and first-principles calculations to uncover a series of high-pressure phases in NiPS3. Remarkably, we find five different states of matter between ambient conditions and 39 GPa—quite different than in the other MPS3 materials. Even more strikingly, infrared spectroscopy and X-ray diffraction combined with a symmetry analysis reveal both metallicity and loss of the inversion center above ~23 GPa suggesting that NiPS3 may be a polar metal with a P3m1 space group under these conditions and P1 symmetry under maximum compression. In addition to identifying a candidate polar metal ripe for further inquiry, we suggest that pressure may tune other complex chalcogenides into this elusive state

High-Field Magnetoelectric and Spin-Phonon Coupling in Multiferroic (NH4)(2)[FeCl5 center dot(H2O)]

We combine high field polarization, magneto-infrared spectroscopy, and lattice dynamics calculations with prior magnetization to explore the properties of (NH4)(2)[FeCl5 center dot(H2O)]-a type II molecular multiferroic in which the mixing between charge, structure, and magnetism is controlled by intermolecular hydrogen and halogen bonds. Electric polarization is sensitive to the series of field-induced spin reorientations, increasing linearly with the field and reaching a maximum before collapsing to zero across the quasi-collinear to collinear-sinusoidal reorientation due to the restoration of inversion symmetry. Magnetoelectric coupling is on the order of 1.2 ps/m for the P parallel to c, H parallel to c configuration between 5 and 25 T at 1.5 K. In this range, the coupling takes place via an orbital hybridization mechanism. Other forms of mixing are active in (NH4)(2)[FeCl5 center dot(H2O)] as well. Magneto-infrared spectroscopy reveals that all of the vibrational modes below 600 cm(-1) are sensitive to the field-induced transition to the fully saturated magnetic state at 30 T. We analyze these local lattice distortions and use frequency shifts to extract spin-phonon coupling constants for the Fe-O stretch, Fe-OH2 rock, and NH4+ libration. Inspection also reveals subtle symmetry breaking of the ammonium counterions across the ferroelectric transition. The coexistence of such varied mixing processes in a platform with intermolecular hydrogen- and halogen-bonding opens the door to greater understanding of multiferroics and magnetoelectrics governed by through-space interactions

Oral health interventions for older people in residential aged care facilities: a protocol for a realist systematic review

Introduction Poor oral health among older people is a global problem impacting on health and well-being. The economic cost to the health system is significant. An ageing population is intensifying the urgency for action. However, poor oral health, particularly for those in residential aged care facilities, continues to be highly resistant to resolution. The overall aims of this realist review are to: (A) explore and synthesise evidence on oral health interventions for older people in residential aged care facilities, (B) produce a causal theory on how contextual factors and mechanisms interact to produce outcomes, and (C) produce guidelines/policies to inform high-quality oral health interventions to improve older people’s oral health in residential aged care facilities.Methods and analysis The review is guided by the RAMESES publication standards for realist synthesis. Participants include older people in residential aged care facilities, the aged care workforce, carers and families. Interventions include oral healthcare, oral health education, policy interventions and oral health promotion. The five-step realist review process of Pawson et al will guide the review: clarification of scope and development of initial framework, systematic searches, study appraisal and data extraction, synthesising evidence, drawing conclusions, and dissemination, implementation and evaluation. Expert input with key stakeholders will occur through a blog. Stakeholders will examine consistencies across studies and an explanatory causal theory will be developed to guide policy and practice.Ethics and dissemination Formal ethical approval was granted by the La Trobe University Ethics Committee HREC 20144. The developed theory will guide education, practice and policy decisions about interventions and the factors that impact on implementation. Using an integrated knowledge translation approach, traditional research outputs such as international conference presentations and publications will be supplemented with stakeholder forums, infographics, blogs, social media postings, webinars, podcasts and writing for web-based independent outlets.PROSPERO registration number CRD42021155658