Browsing by Author "Cadogan, JM"
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- ItemAntiferromagnetic exchange weakening in the TbRhIn5 intermetallic system with Y-substitution(Elsevier, 2018-07-01) Amaral, RP; Lora-Serrano, R; Garcia, DJ; Iwamoto, WA; Betancourth, D; Cadogan, JM; Muñoz-Pérez, S; Avdeev, M; Cobas-Acosta, R; Bittar, EM; Duque, JGS; Pagliuso, PGWe report measurements of the temperature dependent specific heat and magnetic susceptibility in single crystals of the series of intermetallic compounds Tb1−xYxRhIn5 (nominal concentrations x = 0.0, 0.15, 0.3, 0.4, 0.5, 0.7). A mean field approximation to simulate the macroscopic properties along the series has been used. Neutron diffraction data in powdered samples of Tb0.6Y0.4RhIn5 and Tb0.6La0.4RhIn5 reveal antiferromagnetic (AFM) propagation vector k→=[12012] with the magnetic moments oriented along the tetragonal c axis or canted from this axis, respectively for Y and La-substitutions. Considering both the simulations of the magnetic exchange and neutron diffraction data, we discuss the role of combined effects of crystalline electric field (CEF) perturbations and dilution in the evolution of magnetic properties with Y and La contents. In particular, we found negligible variations of the Bnm parameters along the Y series. The decrease of TN with x is fully dominated by magnetic dilution effects. © 2018 Elsevier Ltd.
- ItemAntiferromagnetism weakening with Y-substitution in the TbRhIn5 intermetallic system(arXivLabs, 2017-08-31) Amaral, RP; Lora-Serrano, R; Garcia, DJ; Betancourth, D; Cadogan, JM; Muñoz-Pérez, S; Cobas-Acosta, R; Avdeev, M; Bittar, EM; Duque, JGS; Pagliuso, PGWe report measurements of the temperature dependence specific heat, magnetic susceptibility in single crystals of the series of intermetallic compounds Tb1−xYxRhIn5 (nominal concentrations x=0.15,0.30,0.40,0.50 and 0.70). A mean field approximation to simulate the macroscopic properties along the series has been used. Neutron diffraction data in powdered sample of nominal concentration Tb0.6Y0.4RhIn5 reveal AFM propagation vector k=[12 0 12] with the magnetic moments oriented close to the tetragonal \textit{c} axis. We discuss the role of combined effects of crystalline electric field (CEF) perturbations and dilution in the magnetic properties evolution with Y content. In particular, we suggest that changes in the Tb-In first neighbors distances, i.e. the TbIn3 cuboctahedra distortion, are responsible for changes in the Tb crystalline potential and the possible reorientation of Tb magnetic moments for x>0.4. This reflects non negligible variations of the Bmn crystal field parameters and the energy levels splitting with \textit{x}. CC BY: Creative Commons Attribution
- ItemComplex magnetism of quasi-1D maricite-type NaFePO4(AOCNS 2015, 2015-07-23) Avdeev, M; Piltz, RO; Ling, CD; Auckett, JE; Barpanda, P; Cadogan, JMWe recently reported the magnetic structure of maricite-type NaFePO4 determined using neutron powder diffraction data collected at 3 K1. The crystal structure of this compound is derived from the olivine (Mg2SiO4) type by an ordered distribution of Na and Fe over the two inequivalent Mg sites in the olivine cell. This leads to a magnetically quasi-1D arrangement in which edge-sharing (FeO6) chains are connected to each other only via phosphate groups with a shortest interchain Fe-Fe distance of ~5 Å vs. intrachain distance of ~3.4 Å. Here we report the results of further studies using magnetometry, heat capacity, Mossbauer, and variable field and temperature powder and single crystal neutron diffraction measurements, which reveal not only an intermediate incommensurate magnetic phase existing in zero field within a very narrow interval of ~2 K, but also a metamagnetic transition around 5 T (at 2 K). We will also present and discuss the evolution of the magnetic structure of NaFePO4 as a function of temperature and magnetic field in connection with the crystal structure and compared to that of other maricite type compositions such as AgMnVO42.
- ItemDetermination of the crystal field levels in TmV2Al20(International Conference on Neutron Scattering, 2017-07-12) White, R; Hutchison, WD; Iles, GN; Mole, RA; Cadogan, JM; Namiki, T; Nishimura, K.So called caged rare earth compounds of the RM Al20-type (R = lanthanide, M = transition metal) exhibit interesting physical and magnetic properties at low temperatures. For example PrV Al20 and PrTi Al20 show a quadrupolar Kondo effect [1] and superconductivity [2] brought about by the non-magnetic ground state and the cubic symmetry of the Pr3+site. In this work the compound TmV Al20, a hole analogue of PrV Al20 has been investigated. Previous crystal field calculations based on specific heat and magnetisation [3] resulted in parameters of W = 0.5 K and x = -0.6 within the Lea, Leask and Wolf formalism [4]. However to match the experimental zero field specific heat near 0.5 K, an artificial broadening of the ground state was applied. To validate and clarify these results, we have carried out an inelastic neutron scattering experiment on the PELICAN time-of-flight spectrometer to determine the energy splitting between the crystal field levels. This has allowed a further refinement of the crystal field parameters to W = 0.42(1) K and x = -0.63(1). The very broad Lorentzian line shapes suggest strong 4f-conduction band electron coupling.
- ItemDetermination of the crystal field levels in TmV2Al20(Australian Institute of Physics, 2017-01-31) White, R; Hutchison, WD; Iles, GN; Mole, RA; Cadogan, JM; Namiki, T; Nishimura, KRecent interest in so called caged rare earth compounds of the RM2Al20-type (R = lanthanide, M = transition metal) follow from their fascinating physical and magnetic properties at low temperatures. Recent work on PrV2Al20 and PrTi2Al20 revealed unusual phenomena, including a quadrupolar Kondo effect and superconductivity, brought about by the cubic symmetry of the Pr3+ site inducing a non-magnetic ground state in the ion. As a hole analogue of the PrV2Al20 compound, TmV2Al20 has been investigated for equivalent heavy Fermion behaviour at low temperatures. In previous work, specific heat and magnetisation data were modelled with the crystal field parameters W = 0.5 K and x = -0.6 based on the Lea, Leask and Wolf formalism. However, the experimental zero field specific heat near 0.5 K could only be matched in the modelled curves using an artificial ground state broadening. In this work inelastic neutron scattering data obtained from the PELICAN time of flight spectrometer located at the OPAL reactor, Lucas Heights has allowed further refinement of the values to W = 0.42(1) K and x = -0.63(1). In addition the CEF transitions are found to be very broad, as required for the specific heat, and suggestive of strong 4f-conduction electron coupling.
- ItemDetermination of the crystal field levels in TmV2Al20(Australian Institute of Nuclear Science and Engineering, 2016-11-29) White, R; Hutchison, WD; Iles, GN; Mole, RA; Cadogan, JM; Nishimura, KThere has been increasing interest in compounds of the RM2Al20-type (R = lanthanide, M = transition metal) in recent years due to the unique physical and magnetic properties many have been shown to display at low temperatures. Recent work carried out on PrV2Al20 and PrTi2Al20 has revealed a number of interesting phenomena, including a quadrupolar Kondo effect [1, 2] and superconductivity [3, 4] brought about by the cubic symmetry of the Pr3+ site inducing a non-magnetic ground state in the ion. As a hole analogue of the PrV2Al20 compound, TmV2Al20 has been investigated to see whether it too displays such phenomena at low temperatures. Crystal field calculations based on specific heat and magnetisation have been carried out previously [5] with parameters W = 0.5 K and x = -0.6 determined based on the Lea, Leask and Wolf formalism [6]. These results have been further refined to W = 0.42(1) K and x = -0.63(1) using inelastic neutron scattering data obtained from the PELICAN time-of-flight spectrometer located at the OPAL reactor, Lucas Heights.
- ItemDetermination of the crystal field levels in TmV2Al20(Australian Institute of Physics, 2018-01-31) Hutchison, WD; White, R; Stewart, GA; Iles, GN; Mole, RA; Cadogan, JM; Namiki, T; Nishimura, KThe interest in compounds of the RM2Al20-type (R = lanthanide, M = transition metal) in recent years reflects the fascinating physical and magnetic properties on display at low temperatures. For example, in PrV2Al20 and PrTi2Al20 the phenomena reported include a quadrupolar Kondo effect [1] and superconductivity [2]. Central to such systems is the cubic symmetry of the Pr3+ site inducing a non-magnetic ground state in the ion. As a hole analogue of the PrV2Al20 compound, TmV2Al20 has been investigated in the hope of observing similar phenomena at low temperatures. At last year’s ‘Wagga’ we reported that we had determined the Tm3+ crystal field parameters W = 0.42(1) and x = -0.63(1) [3] (based on the Lea, Leask and Wolf formalism [4]) for TmV2Al20 using inelastic neutron scattering on PELICAN at the OPAL reactor, Lucas Heights. However, the line shapes found were extremely broad Lorentzians, indicative of a coupling of crystal field states to conduction electrons, ‘smearing out’ the energy required for transitions. Here, we report more recent developments: Tm3+ electron spin resonance results together with modelling of physical properties lead to the conclusion that there is a small local distortion away from cubic symmetry.
- ItemThe 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, SJThe 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.
- ItemFirst-order magnetic phase transition in TmGa(Australian Institute of Physics, 2015-02-06) Cadogan, JM; Avdeev, MIn a recent paper we determined the magnetic structure of the intermetallic compound TmGa using a combination of neutron diffraction and 169Tm Mössbauer spectroscopy. This compound shows two magnetic ‘events’ in its ac-susceptibility, at 15(1) K and 12(1) K. The upper transition is to an incommensurate antiferromagnetic structure which gives way to a dominant ferromagnetic structure at the lower transition. However, the Mössbauer results suggested that the 12 K transition is in fact first-order. In order to resolve this question, we have carried out a high-resolution, neutron diffraction thermal scan around these magnetic ordering events and we have observed clear thermal hysteresis in the behaviour of the magnetic scattering intensity. The observation of such hysteresis confirms our earlier suggestion of a first-order magnetic ordering in TmGa.
- ItemMagnetic and structural transitions in magnetocaloric Mn(Co1-xNix)Ge alloys(Australian Institute of Physics, 2017-02-01) Ren, QY; Hutchison, WD; Wang, JL; Studer, AJ; Cadogan, JM; Campbell, SJThe magnetocaloric effect (MCE) - a significant temperature change due to the entropy change around magnetic transitions in materials driven by magnetisation or demagnetisation - has emerged as an increasingly important topic in condensed matter physics in the past two decades. A direct (positive) MCE occurs around a magnetic transition from ferromagnetism (FM) to paramagnetism (PM), while an inverse (negative) MCE is obtained around a magnetic transition from antiferromagnetism (AFM) to FM. If such magnetic transitions couple with a structural transition, a first-order magneto-structural transition can form and hence strengthen the MCE. In this work, the magnetic and structural transitions have been tuned by substitution of Ni for Co in MnCoGe. The Mn(Co1-xNix)Ge samples (x = 0.14 - 1.00) were studied by magnetisation, x-ray and neutron powder diffraction measurements over the temperature range 5 - 450 K. Mn(Co1-xNix)Ge alloys have an orthorhombic (Orth) TiNiSi-type structure (Pnma) at low temperature with transformation to a hexagonal (Hex) Ni2In-type structure (P63/mmc) at the martensitic transformation temperature TM. The increase of the Ni content changes the orthorhombic phase from FM (x < 0.55) to spiral-AFM (x ≥ 0.55). In addition, the transformation temperature TM for the reverse martensitic transformation - from orthorhombic to hexagonal - decreases with Ni content x when x < 0.55 and then increases when x ≥ 0.55. The adjustment of TM leads to the occurrences of first-order FM-Orth/PM-Hex magneto-structural transitions and large values of the direct MCE in the samples with ~0.20 < x < ~0.60. Moreover, the spiral-AFM/FM magnetic transitions in the orthorhombic phase for samples with ~0.55 < x < ~0.75 result in an inverse MCE.
- ItemMagnetic order and spin-reorientation in HoGa(IOP Publishing, 2012-01-01) Susilo, RA; Muñoz-Pérez, S; Cobas, R; Cadogan, JM; Avdeev, MWe have determined the magnetic structure of the intermetallic compound HoGa by high-resolution neutron powder diffraction. This compound crystallizes in the orthorhombic (Cmcm) CrB-type structure and the magnetic structure comprises ferromagnetic order of the Ho sublattice along the c-axis. The Curie temperature is 66(3) K. Upon cooling below 20 K, the Ho magnetic moments cant away from the c-axis towards the ab-plane. At 3 K, the Ho moment is 8.8(2) μB and the Ho magnetic moments point in the direction θ = 30(2)° and phgr = 49(4)° with respect to the crystallographic c-axis. The observation of an ab-plane component at around 50° from the a-axis is in contrast with the suggested magnetic structure of ac order (θ = 32° and phgr = 0°) reported by Delyagin et al. [1] on the basis of a 119Sn Mössbauer spectroscopy study of a Sn-doped HoGa sample. However, we find that these two sets of orientations are in fact indistinguishable by Mössbauer spectroscopy. © Copyright 2021 IOP Publishing
- ItemMagnetic order and spin-reorientations in RGa (R = Dy, Ho and Er) intermetallic compounds(Australian Institute of Physics, 2013-02-06) Susilo, RA; Cadogan, JM; Ryan, DH; Lee-Horne, NR; Cobas, R; Muñoz-Pérez, S; Rosendahl-Hansen, B; Avdeev, MNot available
- ItemMagnetic order and structural properties of Tb2Fe2Si2C(Elsevier, 2016-01-05) Susilo, RA; Cadogan, JM; Hutchison, WD; Avdeev, M; Cobas, R; Muñoz-Pérez, S; Campbell, SJThe structural and magnetic properties of Tb2Fe2Si2C have been investigated by bulk measurements (magnetisation and specific heat), X-ray diffraction, neutron powder diffraction and 57Fe Mössbauer spectroscopy over the temperature range 3 K–300 K Tb2Fe2Si2C is antiferromagnetic with a Néel temperature TN of 44(2) K. The magnetic structure can be described with a propagation vector k = [0 0 ] with the Tb magnetic moments ordering along the b-axis. We also observed strong magnetoelastic effects in particular along the a- and c-axes associated with the antiferromagnetic transition. The 57Fe Mössbauer spectra show no evidence of magnetic splitting down to 10 K, indicating that the Fe atom is non-magnetic in Tb2Fe2Si2C. © 2015 Elsevier B.V.
- ItemMagnetic ordering in Er2Fe2Si2C and Tm2Fe2Si2C(Australian Institute of Physics, 2015-02) Susilo, RA; Cadogan, JM; Hutchison, WD; Campbell, SJ; Avdeev, M; Ryan, DH; Namiki, TThe magnetic ordering of two members of the R2Fe2Si2C (R = rare-earth) series of compounds (monoclinic Dy2Fe2Si2C-type structure with the C2/m space group), Er2Fe2Si2C and Tm2Fe2Si2C, have been studied by neutron powder diffraction and 166Er Mössbauer spectroscopy, complemented by magnetisation and specific heat measurements. In both cases, antiferromagnetic ordering of the R sublattice is observed, with Neel temperatures of 4.8(2) K and 2.6(3) K for Er2Fe2Si2C and Tm2Fe2Si2C, respectively. The magnetic structures of the Erand Tm-based compounds are quite different from those found for the other members of the R2Fe2Si2C series. Previous studies show that the common magnetic structure of the heavy- R2Fe2Si2C compounds involves ordering of the R sublattice along the b-axis with a propagation vector k = [0, 0, ½]. However, the antiferromagnetic structure of the Er sublattice in Er2Fe2Si2C is described by k = [½, ½, 0] with the Er magnetic moments lying close to the ac-plane. Tm2Fe2Si2C is found to exhibit a more complex magnetic structure that is characterised by a square-wave modulation of the Tm magnetic moments along the a-axis and a cell-doubling along the b-axis with k = [0.403(1), ½, 0]. The differences in the magnetic structures of these compounds are interpreted in terms of the RKKY exchange interaction, which depends on the R-R interatomic distances, and crystal field effects acting on the R3+ ions.
- ItemMagnetic ordering in Ho2Fe2Si2C(American Institute of Physics, 2015-02-23) Susilo, RA; Cadogan, JM; Cobas, R; Hutchison, WD; Avdeev, M; Campbell, SJWe have used neutron diffraction and 57Fe M€ossbauer spectroscopy, complemented by magnetisation and specific heat measurements, to examine the magnetic ordering of Ho2Fe2Si2C. We have established that Ho2Fe2Si2C orders antiferromagnetically below TN¼ 16(1) K with a magnetic structure involving ordering of the Ho sublattice along the b-axis with a propagation vector k ¼ ½0 0 12. 57Fe M€ossbauer spectra collected below TN show no evidence of a magnetic splitting, demonstrating the absence of long range magnetic ordering of the Fe sublattice. A small line broadening is observed in the 57Fe spectra below TN, which is due to a transferred hyperfine field—estimated to be around 0.3 T at 10 K—from the Ho sublattice. VC 2015 AIP Publishing LLC.
- ItemMagnetic ordering in TmGa(IOP Science, 2014-03-03) Cadogan, JM; Stewart, GA; Muñoz-Pérez, S; Cobas, R; Hansen, BR; Avdeev, M; Hutchison, WDWe have determined the magnetic structure of the intermetallic compound TmGa by high-resolution neutron powder diffraction and 169Tm Mössbauer spectroscopy. This compound crystallizes in the orthorhombic (Cmcm) CrB-type structure and its magnetic structure is characterized by magnetic order of the Tm sublattice along the a-axis. The initial magnetic ordering occurs at 15(1) K and yields an incommensurate antiferromagnetic structure described by the propagation vector k1 = [0 0.275(2) 0]. At 12 K the dominant ferromagnetic ordering of the Tm sublattice along the a-axis develops in what appears to be a first-order transition. At 3 K the magnetic structure of TmGa is predominantly ferromagnetic but a weakened incommensurate component remains. The ferromagnetic Tm moment reaches 6.7(2) μB at 3 K and the amplitude of the remaining incommensurate component is 2.7(4) μB. The 169Tm hyperfine magnetic field at 5 K is 631(1) T. © Copyright IOP Publishing
- ItemMagnetic phase transitions in layered NdMn2Ge2-xSix(Australian Institute of Physics, 2010-02-05) Wang, JL; Campbell, SJ; Cadogan, JM; Studer, AJ; Zeng, R; Dou, SXThe discovery of a giant magnetocaloric effect (GMCE) near room temperature in Gd5Si2Ge2 has led to much attention being paid to layered structures in order to understand the MCE behaviour of such materials [1]. NdMn2Ge2-xSix offers interesting prospects for enhanced magnetocaloric behaviour as the tetragonal, layered structure allows the structural and magnetic states to be controlled via inter- and intra-planar separations of the Mn atoms. We have investigated the structural and magnetic behaviour of NdMn2Ge2-xSix (x=0-2.0) by magnetic measurements, X-ray and neutron diffraction (Wombat, OPAL) over the temperature range 6-465 K. Replacement of Ge by Si leads to contraction of the unit cell with lattice constant a of NdMn2Ge2-xSix passing through two critical values a crit1 and a crit2 in RMn2X2 [2]: a crit1=4.06 Å at x1∼.0 and a crit2=4.02 Å at x∼1.8. This leads to significant modifications of the magnetic states of NdMn2Ge2-xSix. For example, at room temperature both NdMn2Ge1.6Si0.4 and NdMn2Ge1.2Si0.8 are found to exhibit canted ferromagnetism (Fmc) while NdMn2Ge0.8Si1.2 and NdMn2Ge0.4Si1.6 show canted antiferromagnetism (AFmc). By comparison, NdMn2Si2.0 exhibits interlayer antiferromagnetism (AFil) at 300 K [3]. We have established that Fmc and AFmc co-exist for NdMn2Ge1.2Si0.8 between TCNd (9∼0 K) and TNinter (∼180K) while NdMn2Ge0.4Si1.6 has a GMCE value of -∆SMmax=18.4 J kg -1 K -1 around TCNd=36 K for a field change ∆B = 5 T. The overall magnetic behaviours of NdMn2Ge2-xSix compounds are governed by the strong dependence of the magnetic couplings on the Mn-Mn spacing within the ab-plane. A detailed magnetic phase diagram for the NdMn2Ge2-xSix system has been constructed over the entire temperature and composition ranges.
- ItemMagnetic properties of PrMn1.2Fe0.8Ge2(Elsevier, 2006-11-15) Wang, JL; Studer, AJ; Campbell, SJ; Hofmann, M; Cadogan, JMAs part of our investigation of the PrMn2-xFexGe2 series we have investigated the magnetic structures of PrMn1.2Fe0.8Ge2 (space group I4/mmm) by powder neutron diffraction and magnetic measurements. The Mn moments in PrMn1.2Fe0.8Ge2 exhibit only antiferromagnetic ordering whereas for lower Fe concentrations, x≤0.6, the Mn-sublattice exhibits ferromagnetic ordering. Two magnetic phase transitions take place with decreasing temperature in PrMn1.2Fe0.8Ge2. The first transition from paramagnetism to intralayer antiferromagnetic order (AFl) within the (0 0 1) Mn layers occurs at TN intra∼242 K. The second transition occurs at TN inter∼154 K; this transition is related to the change from the intralayer antiferromagnetic state to the antiferromagnetic mixed commensurate magnetic structure (AFmc). The neutron data also reveal an anisotropic thermal expansion within the interplanar antiferromagnetic region (-0.39% in the a-axis and+0.25% in the c-axis from∼160 to 3 K). © 2006 Elsevier B.V.
- ItemMagnetic properties of the 6H perovskite Ba3Fe2TeO9(Elsevier, 2017-09-01) Tang, YW; Paria Sena, R; Avdeev, M; Battle, PD; Cadogan, JM; Hadermann, J; Hunter, ECA polycrystalline sample of Ba3Fe2TeO9 having the 6H perovskite structure has been prepared in a solid-state reaction and studied by a combination of electron microscopy, Mössbauer spectroscopy, magnetometry, X-ray diffraction and neutron diffraction. Partial ordering of Fe3+ and Te6+ cations occurs over the six-coordinate sites; the corner-sharing octahedra are predominantly occupied by the former and the face-sharing octahedra by a 1:1 mixture of the two. On cooling through the temperature range 18 < T/K < 295 an increasing number of spins join an antiferromagnetic backbone running through the structure while the remainder show complex relaxation effects. At 3 K an antiferromagnetic phase and a spin glass coexist. © 2017 The Authors. Creative Commons license Published by Elsevier Inc.
- ItemMagnetic structure and spin reorientation of quaternary Dy2Fe2Si2C(IOP Publishing, 2017-02-07) Susilo, RA; Cadogan, JM; Hutchison, WD; Stewart, GA; Avdeev, M; Campbell, SJWe have investigated the low temperature magnetic properties of Dy2Fe2Si2C by using magnetisation, specific heat, x-ray diffraction, neutron powder diffraction and 57Fe Mössbauer spectroscopy measurements over the temperature range 1.5 K–300 K. Dy2Fe2Si2C exhibits two magnetic transitions at low temperatures: an antiferromagnetic transition at ${{T}_{\text{N}}}\sim 26$ K and a spin-reorientation transition at ${{T}_{t}}\sim 6$ K. The magnetic structure above Tt can be described with a propagation vector $\mathbf{k}~=~\left(0~0~\frac{1}{2}\right)$ with the ordering of the Dy magnetic moments along the monoclinic b-axis whereas on cooling below Tt the Dy moment tips away from the b-axis towards the ac-plane. We find that the spin-reorientation in Dy2Fe2Si2C is mainly driven by the competition between the second-order crystal field term B20 and the higher-order terms, in particular B40 and B64. © 2017 IOP Publishing Ltd