ANSTO :: Browsing by Author "Rule, KC"

Browsing by Author "Rule, KC"

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2nd Asia-Oceania Instrument Scientist Workshops, Manly, July 19, 2015
(Taylor & Francis Online, 2015-11-17) Hester, JR; Holt, SA; Imperia, P; Piltz, RO; Rehm, C; Rule, KC; Mole, RA; McIntyre, GJ
No abstract available
Asymmetric thermal line shape broadening in a gapped 3D antiferromagnet: evidence for strong correlations at finite temperature
(American physical Society, 2012-09-19) Quintero-Castro, DL; Lake, B; Islam, ATMN; Wheeler, EM; Balz, C; Mansson, M; Rule, KC; Gvasaliya, S; Zheludev, A
It is widely believed that magnetic excitations become increasingly incoherent as the temperature is raised due to random collisions which limit their lifetime. This picture is based on spin-wave calculations for gapless magnets in 2 and 3 dimensions and is observed experimentally as a symmetric Lorentzian broadening in energy. Here, we investigate a three-dimensional dimer antiferromagnet and find unexpectedly that the broadening is asymmetric-indicating that far from thermal decoherence, the excitations behave collectively like a strongly correlated gas. This result suggests that a temperature activated coherent state of quasiparticles is not confined to special cases like the highly dimerized spin-1/2 chain but is found generally in dimerized antiferromagnets of all dimensionalities and perhaps gapped magnets in general. © 2012, American Physical Society.
Chemical disorder in a frustrated J1/J2 quantum spin chain material
(Australian Institute of Physics, 2018-01-30) Rule, KC; Mole, RA; Zanardo, J; Krause-Heuer, AM; Darwish, TA; Lerch, MLF
Recently a new one-dimensional (1D) quantum spin chain system has been synthesised: catena-dichloro(2-Cl-3Mpy)copper(II), [where 2-Cl-3Mpy=2-chloro-3-methylpyridine]. We shall refer to this compound as cd-Cu. Preliminary calculations and bulk magnetic property measurements indicate that this system does not undergo magnetic ordering down to 1.8K and is a prime candidate for investigating frustration in a J1/J2 system (where the nearest neighbour interactions, J1, are ferromagnetic and the next nearest neighbour interactions, J2, are antiferromagnetic) [1]. Calculations predicted 3 possible magnetic interaction strengths for J1 below 6meV depending on the orientation of the ligand [2]. For one of the predicted J1values, the existence of a quantum critical point is implied. A deuterated sample of cd-Cu was produced at the National Deuteration Facility and the excitations measured using the PELICAN TOF spectrometer. Scattering was weak from this sample, but indicated the most likely scenario involves an average of the 3 possible magnetic excitations in this material, rather than the random array of exchange interactions as predicted by Herringer et al., [2]. This may indicate the possibility of tuning the chemical structure to favour a system which may exhibit a quantum critical point.
Commensurate to incommensurate magnetic phase transition in the type-II multiferroic YBaCuFeO5
(Australian Institute of Physics, 2015-02-06) Lai, YC; Chen, WT; Wang, CW; Rule, KC; Chou, FC; Du, CH
The simultaneous existence of magnetic and ferroelectric ordering is a characteristic of multiferroic materials. The search for new multiferroics is partly motivated by the need for non-volatile random access memories for which the electric polarisation (magnetisation) is controlled by magnetic field (electric field) or vice versa. The use of such materials would be extremely beneficial for the next generation of electronic devices (mobile phones, tablets etc) whereby compact size constraints are important as well as optimising reading/writing speeds and power consumption. YBaCuFeO5 has been classified as a type-II multiferroic due to its complex magnetic interactions and low temperature feroelectricity. Two magnetic phase transitions of antiferromagnetic nature have been found near TN1 = 450 K and TN2 = 170 K. The first represents the ordering of the Fe3+ ions into a commensurate antiferromagnetic state, while the second represents the ordering of the Cu2+ ions giving an overall incommensurate antiferromagnetic ground state. For the first time, using modified traveling solvent floating zone growth method, we have been able to grow a centimeter-sized, high-quality, singlecrystal of YBaCuFeO5. Magnetisation and neutron diffraction results indicate a complex magnetic phase diagram in this material with a strong hysteresis effect and a chiral magnetic ground state.
Comparing inelastic neutron scattering with theory to understand the complex magnetic interactions in a low-dimensional frustrated magnet
(Australian Institute of Nuclear Science and Engineering (AINSE), 2020-11-11) Allen, J; Rule, KC; Mole, RA; Heinze, L; Süllow, S
Frustrated magnetic systems have gained a lot of recent interest as they can exhibit exotic magnetic quantum states such as spin-liquid and spin-nematic states [1,2]. The natural mineral atacamite, Cu2Cl(OH)3, is one such material which has been reported to exhibit magnetic behaviour characteristic of a frustrated quantum magnet [3]. It also shares structural similarity with another cuprate, herbertsmithite, whose kagomé lattice is predicted to host a spin liquid ground state [4]. Little is understood about the magnetic properties of the natural orthorhombic structure of atacamite in contrast to its other structural polymorphs. This work studies this lesser understood orthorhombic atacamite, where Cu2+ ions form a pyrochlore lattice. The novel magnetic interactions and quantum states in materials like atacamite lends itself to spintronic applications where understanding spin interactions can unveil opportunities for intentionally manipulating these spins. Time-of-flight inelastic neutron scattering measurements on single crystalline atacamite have been performed at Pelican with an incident wavelength of 4.69Å. Excitations were observed at 1.5K, and weakened as temperature was increased beyond the antiferromagnetic transition temperature of TN = 9.0K [5] to 20K. The strongest dispersion was found along the H00 direction with two nested modes observed up to an energy transfer of 3meV. Relatively weak dispersion was seen along 00L, and a flat mode was observed in out-of-plane scattering covering a narrow section in 0K0. Ab initio band structure calculations have indicated a 1D sawtooth chain model for the dominant magnetic exchange paths in atacamite [6]. This chain model can be consolidated with our neutron scattering measurements and SpinW calculations. However, the relative magnitudes and directions of the predicted exchange couplings indicate the strongest interactions to be along 0K0, and this does not agree with the strongest dispersion measured experimentally in the H00 direction at zero field. To better understand the interactions in atacamite, in-field time-of-flight measurements have also been conducted in magnetic fields up to 6.5T, applied along the crystallographic b-axis. Data were collected using Pelican and the new open geometry, fully compensated, 7T vertical magnet. We will present the results of these inelastic neutron scattering measurements along with corresponding SpinW calculations to address the inconsistencies between theory and data when considering the exchange interactions in atacamite.
Complex magnetic incommensurability in multiferroic Co3TeO6
(International Conference on Neutron Scattering, 2017-07-12) Lee, CH; Wang, CW; Zhao, Y; Li, WH; Lynn, JW; Harris, AB; Rule, KC; Yang, HD; Berger, H
Monoclinic cobalt tellurate Co3TeO6 has been characterized1-3 as a type-II multiferroic, where the order parameters of electrical polarization and spontaneous magnetization are closely coupled.4,5 In this study, polarized and unpolarized neutron diffractions have been carried out to investigate the nature of the magnetic structures and transitions in monoclinic Co3TeO6. As the temperature is lowered below TM1= 26 K long range order develops, which is fully incommensurate (ICM) in all three crystallographic directions in the crystal. Below TM2 = 19.5 K, additional commensurate magnetic peaks develop, consistent with the ?4 irreducible representation, along with a splitting of the ICM peaks along the h direction which indicates that there are two separate sets of magnetic modulation vectors. Below TM3 = 18 K, this small additional magnetic incommensurability disappears, ferroelectricity develops, a commensurate ?3 irreducible representation appears, and the k component of the ICM wave vector disappears. Below TM4= 15 K the k component of the ICM structure reappears, along with second-order ICM Bragg peaks, which polarized neutron data demonstrate are magnetic in origin.
Crystal field interactions in the chiral compounds RNi3Ga9 (R = Tb, Dy, Ho and Er) studied by inelastic neutron scattering
(Australian Institute of Nuclear Science and Engineering (AINSE), 2020-11-11) Gil, L; Lora-Serrano, R; Duque, JGS; Garcia, DJ; Cadogan, S; Rule, KC
In recent years, compounds with chiral structures have attracted much attention mainly because of noncollinear and non-coplanar spin textures, which have an important application in spintronics. In chiral compounds, the lack of inversion symmetry can give rise to an asymmetric spin interaction, the so-called Dzyaloshinskii-Moriya interaction, which contributes to the symmetric exchange interaction and anisotropy effects from the crystal field. These interactions’ coexistence can result in unusual magnetic properties and exotic magnetic structures with potential for many applications and novel phenomena. In this work, we study the magnetic properties of the chiral compounds RN i3Ga9 (R = Tb, Dy, Ho and Er), which crystalize in a trigonal ErNi3Al9-type structure with non-centrosymmetric space group R32 [1]. For this purpose, we analyzed the inelastic neutron scattering (INS) spectra in powder samples at several temperatures (T) to study the crystal electric field (CEF) excitations and ground-state. The INS experiments were performed at the SIKA beamline using the cold triple-axis spectrometer. The spectrum was analyzed at four temperatures for ErN i3Ga9 (T = 8, 20, 50 and 100K) and two temperatures for T bN i3Ga9 (T = 50 and 100K), HoN i3Ga9 (T = 30 and 100K) and DyN i3Ga9 (T = 50 and 100K). Moreover, transverse and longitudinal magnetic susceptibility was measured in single-crystalline samples to fit the CEF parameters better. We developed a code based on the magnetic susceptibility and differential cross-section for magnetic scattering at low Q (dipole approximation) to process and analyze the experimental data. The effective CEF hamiltonian for the system follows the C3 point symmetry, which results in 9 CEF parameters overall. The least-square fitting procedure uses a machine-learning algorithm based on particle swarm optimization. We report the energy levels scheme due to the crystal field and the CEF ground state’s eigenfunctions. In particular, the INS spectra for the ErNi3Ga9 compound showed peaks associated with the so-called hot transitions, which take place between excited energy levels. We only observed peaks associated with transitions between the ground-state and the first excited levels for R = Ho, Tb, and Dy. The calculated INS spectra and magnetic susceptibility were in good agreement with the experimental data. In particular, the calculated magnetic susceptibility showed that the direction of easy magnetization occurs along the c-axis for the ErNi3Ga9 compound and along the basal plane for the other compounds. It evidences the oblate and prolate nature of the rare-earth ions charge distributions. In summary, we used inelastic neutron scattering data to establish the CEF parameters for all compounds according to the C3 point symmetry. The obtained parameters describe the CEF energy levels’ configuration and the relative intensity of the peaks observed in the INS spectrum, besides the transverse and longitudinal magnetic susceptibility in the paramagnetic region.
Crystal growth and characterisation of a new J1-J2 spin-chain material
(Australian Institute of Nuclear Science and Engineering, 2016-11-29) Zanardo, J; Rule, KC; Krause-Heuer, AM; Mole, RA; Lerch, MLF
Recently a new one-dimensional (1D) quantum spin chain system has been synthesised: catena-dichloro(2-Cl-3Mpy)copper(II), [where 2-Cl-3Mpy=2-chloro-3-methylpyridine] [1]. Preliminary calculations and bulk magnetic property measurements indicate that this system does not undergo magnetic ordering down to 1.8K and is a prime candidate for investigating frustration in a J1/J2 system (where the next nearest neighbour interactions, J2, are antiferromagnetic and the nearest neighbour interactions, J1, are ferromagnetic) [2]. Calculations predict 3 possible magnetic excitations below 6meV which may reveal the nature of the random static structural disorder predicted in this material. One method for directly observing the magnetic excitations is neutron scattering and measurements have been performed on the neutron Time of Flight spectrometer PELICAN at ANSTO [3]. To a first approximation, linear spin-wave theory has been used to model the expected neutron excitations for this J2/J1 system using the Matlab package SpinW. The results of this project may provide valuable insight into the nature of magnetic frustration in materials. To optimise the observed magnetic signal via the reduction of incoherent neutron scattering, this compound was deuterated at the National Deuteration Facility at ANSTO. In this presentation we will outline our deuterated growth procedure as well as the characterisation methods performed to understand the material further. This work forms the Honours thesis project of Jack Zanardo from University of Wollongong.
Current high-pressure capabilities at ACNS and future plans
(Australian Institute of Nuclear Science and Engineering (AINSE), 2020-11-11) Maynard-Casely, HE; Booth, N; Shumack, A; Baldwin, C; White, R; Rule, KC; McIntyre, GJ; Novelli, G
High-pressure (>1 Kbar) is a marvellous variable, which can reveal mechanical properties, structural transitions and exotic behaviours. This pairs very well with neutron scattering, where the highly penetrating nature of neutron beams is idea for accessing sample within complex sample environments. The Australian Centre for Neutron Scattering (ACNS) has developed a number of capabilities for high-pressure experiments, mainly revolving around the use of our Paris-Edinburgh press but more recently with miniature diamond-anvil cells. Some of these, such as our ability to compress radioactive samples as well as combining high-pressure and high-electric fields are unique in the world. Here we review the high pressure capabilities at ACNS, and outline some directions for capabilities and measurements.
Data-processing technique for the Taipan “Be-filter” neutron spectrometer at the Australian Nuclear Science and Technology Organisation
(American Institute of Physics (AIP), 2021-07-09) Iles, GN; Rule, KC; Peterson, VK; Stampfl, APJ; Elcombe, MM
There are five filter-analyzer neutron spectrometers available worldwide for scientists to use in order to measure the vibrational density of states in various samples. While Taipan, the thermal spectrometer, has been operated as a triple-axis spectrometer at the Australian Centre for Neutron Scattering since 2010, a beryllium filter analyzer spectrometer was added in 2016. Due to the complex nature of the data post-processing, it has thus far been impossible to fully treat experimental data from scientific measurements taken over the last five years. We have successfully created a robust method of treating data from the Taipan filter-analyzer and present the method on three different samples. The data-treatment process includes correction for the non-linear energy variation of a particular monochromator, removal of higher-order wavelength contamination, and estimation of low-energy multiple-scattering. The steps described here can be utilized by all users of the Australian Nuclear Science and Technology Organisation “Be-filter”—past, present, and future. © 2021 Author(s). Published under an exclusive license by AIP Publishing.
Diffuse scattering studies from a martensitic Fe-Pd alloy
(Australian Institute of Physics, 2022-12-11) Finlayson, TR; McIntyre, GJ; Rule, KC
Results from the Koala, Taipan and Sika instruments at the OPAL reactor, ANSTO, reveal two martensitic transformations for an Fe-30at%Pd crystal between 400 to 100K. These results will be discussed in this poster presentation.
Diffuse scattering studies from a martensitic Fe-Pd alloy
(Australian Institute of Nuclear Science and Engineering (AINSE), 2020-11-11) McIntyre, GJ; Rule, KC; Finlayson, TR
From literatrure reports, Fe-Pd alloys in the vicinity of Fe-30at%Pd exhibit two martensitic transformations on being cooled from just above room temperature to about 100K. A preliminary study of a large single crystal of this composition at the KOALA beamline, not only showed evidence for these transformations but also revealed most interesting satellite reflections around certain Bragg reflections. The crystal has been studied further in two triple-axis experiments. The first was at TAIPAN, specifically to study elastic scattering and the second, at SIKA, to study quasi-elastic scattering both in the vicinity of certain Bragg peaks but also around the satellite reflections observed at KOALA. The results from both of these experiments will be discussed. © The Authors
Down the rabbit hole: a journey into the curiouser and curiouser world of low-dimensional, copper-oxide, quantum-magnets
(Australian Institute of Physics, 2019-02-07) Rule, KC
Low dimensional quantum magnets offer a rich playground with which we can explore competing magnetic interactions, which can include frustration, anisotropy effects as well as the weak interactions afforded by separating magnetic ions into reduced dimensional topologies. This can lead to a whole host of exotic ground states and exited phases. I would like to talk about a few systems which we have studied recently - systems which do not appear to behave classically. In particular I would like to highlight the role of inelastic neutron scattering and extreme sample environments which have been employed to probe the world of low dimensional magnets. As part of this presentation I will discuss recent results on Linarite and Atacamite as well as future materials we plan to study. In particular the role of theoretical modelling will be highlighted throughout this talk.
The dynamics and critical properties of FePS3, an Ising-like twodimensional magnet on a honeycomb lattice
(Australian Institute of Physics, 2014-02-05) Wildes, A; Rule, KC; Lançon, D; Hicks, T
The MPS3 compounds (M = transition metal) are a family of materials where the M2+ ions lie in planes forming a honeycomb lattice. The planes are weakly bound by van der Waals forces and, when the M2+ carries a magnetic moment, the materials are good approximations of two-dimensional (2D) antiferromagnets. The FePS3 compound is of particular interest as it is a rare example of an Ising-like 2D magnet with honeycomb symmetry [1]. We have performed experiments with neutron scattering to investigate the magnon dynamics on both a powder [2] and, more recently, on a single crystal. We have further made extensive measurements of the critical dynamics of the compound. We will present our results, showing the magnon dispersion surface and the magnitudes of the exchange interactions along with the scaling behaviour of the magnetization and the anisotropy. The results will be contrasted with a sister compound, MnPS3, which is a good example of a Heisenberg-like 2D magnet. We will also discuss the possibilities for tricritical points and quantum phase transitions in this compound.
The elusive magnetic structure of FePS3
(Australian Institute of Physics, 2003-02-04) Rule, KC; McIntyre, GJ; Kennedy, SJ; Hicks, TJ
Laue diffraction patterns from a single crystal of FePS3 were recorded at temperatures above and below the Néel temperature TN = 120 K on the new thermal Laue diffractometer VIVALDI at the Institut Laue Langevin. Magnetic peaks were weaker and more extended than the nuclear peaks. The directions in reciprocal space of the magnetic reflections were found by reference to the nuclear peaks, and the magnetic reflections could then be readily located on the monochromatic diffractometer D19. The strongest magnetic peaks were found at 0.5, -0.5, 0.34 and 1.5, -0.5, 0.34 and symmetry related positions.
Experimental observation and computational study of the spin-gap excitation in Ba3BiRu2O9
(American Physical Society, 2016-11-01) Ling, CD; Huang, Z; Kennedy, BJ; Rols, S; Johnson, MR; Zbiri, M; Kimber, SAJ; Hudspeth, J; Adroja, DT; Rule, KC; Avdeev, M; Blanchard, PER
Ba3BiRu2O9 is a 6H-type perovskite compound containing face-sharing octahedral M2O9 (M=Ir, Ru) dimers, which are magnetically frustrated at low temperatures. On cooling through T∗=176 K, it undergoes a pronounced magnetostructural transition, which is not accompanied by any change in space group symmetry, long-range magnetic ordering, or charge ordering. Here, we report the first direct evidence from inelastic neutron scattering that this transition is due to an opening of a gap in the excitation spectra of dimers of low-spin Ru4+ (S=1) ions. X-ray absorption spectroscopy reveals a change in Ru-Ru orbital overlap at T∗, linking the emergence of this spin-gap excitation to the magnetostructural transition. Ab initio calculations point to a geometrically frustrated magnetic ground state due to antiferromagnetic interdimer exchange on a triangular Ru2O9 dimer lattice. X-ray total-scattering data rule out long-range magnetic ordering at low temperatures, consistent with this geometrically frustrated model. ©2016 American Physical Society
Few-layer hexagonal boron nitride / 3D printable polyurethane composite for neutron radiation shielding applications
(Elsevier, 2023-03) Knott, JC; Khakbaz, HS; Allen, J; Wu, L; Mole, RA; Baldwin, C; Nelson, A; Sokolova, AV; Beirne, S; Innis, PC; Frost, DG; Cortie, DL; Rule, KC
Functional polymer composites can confer a range of benefits in practical applications that go beyond the individual properties of the constituent materials. Here we investigate and characterize the neutron absorbing capability of few-layer hexagonal boron nitride (h-BN) in composite with a 3D-printable thermoplastic polyurethane, and present experiment and simulation data to understand the processes and mechanisms in play. Shielding and protection from neutrons can be necessary in a range of terrestrial and space-based applications. The neutron absorption of composites with varying fractions of h-BN is strongly energy-dependent in the low-energy regime below 10 meV, and a composite containing 20 wt% h-BN shows a 70-fold reduction in the transmission relative to pure polyurethane at 0.5 meV neutron energies. This is attributed to the strong neutron capture cross-section of the naturally abundant boron-10 isotope, with energy-dependent measurements up to 100 meV confirming this point. Using inelastic neutron spectroscopy, we identify additional effects from the hydrogen in the polyurethane which both scatters diffusively and moderates neutrons inelastically via its phonon spectrum, enhancing the neutron absorption characteristics. Two models – based on analytic functions and Monte Carlo numerical techniques – are presented, and show excellent agreement with experiment results. The 3D-printability of the composite is demonstrated, and the opportunities and challenges for deploying these composites in neutron radiation protection applications are discussed. © 2022 Published by Elsevier Ltd.
First extensive study of lanthanum manganite nanoparticles to target deadly brain cancer
(Australian Institute of Nuclear Science and Engineering (AINSE), 2020-11-11) Khochaiche, A; Westlake, M; O'Keefe, A; Engels, E; Li, N; Vogel, S; Valceski, M; Konstantinov, K; Corde, S; Lerch, MLF; Tehei, M; Rule, KC; Horvat, J
The ability to successfully target deep-seated tumours in sensitive areas of the body is limited to adequate targeting strategies. More specifically, brain and central nervous system (CNS) cancers can be the most aggressive, have higher mortality rates and lower accessibility to chemotherapeutic drugs. A proposed solution to target these concerns is through introducing high atomic number (Z) nanoparticles (NPs) such as silver-doped lanthanum manganite (LAGMO) to aid in common treatments such as radiation therapy. These NPs can bypass the blood brain barrier and are capable of increasing the damage from the radiation due to their high-Z. Most importantly they have potential to cause cancer cells to undergo hyperthermia (a cell death precursor) as the NPs heat up in their environment due to their Curie temperature being in the hyperthermia range of interest.
First extensive study of silver-doped lanthanum manganite nanoparticles for inducing selective chemotherapy and radio-toxicity enhancement
(Elsevier B. V., 2021-04) Khochaiche, A; Westlake, M; O'Keefe, A; Engels, E; Vogel, S; Valceski, M; Li, N; Rule, KC; Horvat, J; Konstantinov, K; Rosenfeld, AB; Lerch, MLF; Corde, S; Tehei, M
Nanoparticles have a great potential to increase the therapeutic efficiency of several cancer therapies. This research examines the potential for silver-doped lanthanum manganite nanoparticles to enhance radiation therapy to target radioresistant brain cancer cells, and their potential in combinational therapy with magnetic hyperthermia. Magnetic and structural characterisation found all dopings of nanoparticles (NPs) to be pure and single phase with an average crystallite size of approximately 15 nm for undoped NPs and 20 nm for silver doped NPs. Additionally, neutron diffraction reveals that La0.9Ag0.1MnO3 (10%-LAGMO) NPs exhibit residual ferromagnetism at 300 K that is not present in lower doped NPs studied in this work, indicating that the Curie temperature may be manipulated according to silver doping. This radiobiological study reveals a completely cancer-cell selective treatment for LaMnO3, La0.975Ag0.025MnO3 and La0.95Ag0.05MnO3 (0, 2.5 and 5%-LAGMO) and also uncovers a potent combination of undoped lanthanum manganite with orthovoltage radiation. Cell viability assays and real time imaging results indicated that a concentration of 50 μg/mL of the aforementioned nanoparticles do not affect the growth of Madin-Darby Canine Kidney (MDCK) non-cancerous cells over time, but stimulate its metabolism for overgrowth, while being highly toxic to 9L gliosarcoma (9LGS). This is not the case for 10%-LAGMO nanoparticles, which were toxic to both non-cancerous and cancer cell lines. The nanoparticles also exhibited a level of toxicity that was regulated by the overproduction of free radicals, such as reactive oxygen species, amplified when silver ions are involved. With the aid of fluorescent imaging, the drastic effects of these reactive oxygen species were visualised, where nucleus cleavage (an apoptotic indicator) was identified as a major consequence. The genotoxic response of this effect for 9LGS and MDCK due to 10%-LAGMO NPs indicates that it is also causing DNA double strand breaks within the cell nucleus. Using 125 kVp orthovoltage radiation, in combination with an appropriate amount of NP-induced cell death, identified undoped lanthanum manganite as the most ideal treatment. Real-time imaging following the combination treatment of undoped lanthanum manganite nanoparticles and radiation, highlighted a hinderance of growth for 9LGS, while MDCK growth was boosted. The clonogenic assay following incubation with undoped lanthanum manganite nanoparticles combined with a relatively low dose of radiation (2 Gy) decreased the surviving fraction to an exceptionally low (0.6 ± 6.7)%. To our knowledge, these results present the first biological in-depth analysis on silver-doped lanthanum manganite as a brain cancer selective chemotherapeutic and radiation dose enhancer and as a result will propel its first in vivo investigation. © 2021 Elsevier B.V.
The frustrated quantum spin chain, linarite, in high magnetic fields
(Australian Institute of Nuclear Science and Engineering, 2016-11-29) Willenberg, B; Nishimoto, S; Schaepers, M; Reehuis, M; Wolter, AUB; Drechsler, SL; Buechner, B; Studer, AJ; Rule, KC; Ouladdiaf, B; Suellow, S
Linarite, PbCuSO4(OH)2 is a natural mineral ideally suited to the study of frustration in J1-J2 systems due to an accessible saturation field and the availability of large single crystals well suited to neutron investigations. In this one dimensional J1-J2 model, competing ferromagnetic nearest-neighbour interactions (J1>0) and antiferromagnetic next-nearest-neighbours (J2<0) can give rise to novel phenomena such as multiferroicity for spiral spin states. It is also predicted that materials which exhibit such frustrated magnetic interactions are likely to display evidence of spin-nematic states. The magnetic spin-nematic phase can be likened to the arrangement of molecules in nematic liquid crystal displays (LCD). The magnetic form of the spin-nematic state, involves the ordering of spin-quadrupole moments in the absence of conventional spin-dipole order such that the magnetic spins align spontaneously along a chosen axis while still fluctuating dynamically. In Linarite, the Cu2+ ions form spin S = 1/2 chains along the b direction with dominant nearest neighbour FM interactions and a weaker next-nearest-neighbour AFM coupling, resulting in a magnetically frustrated topology [1, 2]. We present a neutron scattering and magnetic property study of linarite revealing a helical magnetic ground state structure with an incommensurate propagation vector of (0 0.186 ½) below TN = 2.8K in zero magnetic field [3]. From detailed measurements in magnetic fields up to 12 T (B || b), a very rich magnetic phase diagram will be presented (Fig. 1) [4]. A two-step spin-flop transition is observed, transforming the helical magnetic ground state into a collinear structure. As well, a magnetic phase with sine-wave modulated moments parallel to the field direction was detected, enclosing the other long-range ordered phases, and which exhibits phase separation in high magnetic fields. Theoretical calculations imply that linarite possesses an xyz exchange anisotropy. Our data establish linarite as a model compound of the frustrated one-dimensional spin chain, with ferromagnetic nearest-neighbour and antiferromagnetic next-nearest-neighbour interactions. We shall also discuss the high field phase (marked “?” in the phase diagram of Fig. 1) in terms of the spin-nematic physics as well as the hard to access regions of the phase diagram, namely Region II.

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