Browsing by Author "Battle, PD"

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    Antiferromagnetism and metamagnetism in ErFeCuGe4O12
    (Elsevier, 2018-09-15) Xu, D; Avdeev, M; Battle, PD
    Polycrystalline ErFeCuGe4O12 has been prepared in a solid-state reaction. It adopts a tetragonal crystal structure; space group P4/nbm with a = 9.6416(1), c = 4.7532(1) at room temperature. The Er3+ cations are in square-antiprismatic coordination and the Fe3+ and Cu2+ cations are disordered over one six-coordinate site. The magnetic moments of the three cations adopt an antiferromagnetic arrangement on cooling below 20 K in H = 0 kOe. The magnetic structure consists of ferromagnetic (001) sheets with the spin direction in neighbouring sheets alternating between [001] and [00 ̅At 5 K the ordered moment of Er3+ was determined by neutron diffraction to be 7.90(3) µB and the mean moment of Fe3+ and Cu2+ was 2.43(2) µB. The magnetic structure is unchanged in an applied field of 10 kOe but in fields ≥ 20 kOe the compound begins a metamagnetic transition to a ferromagnetic structure with all atomic moments aligned along [001]. © 2018 Elsevier Inc.
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    Experimental and computational study of the magnetic properties of ZrMn2−xCoxGe4O12
    (Royal Society of Chemistry, 2017-05-15) Xu, D; Sale, M; Avdeev, M; Ling, CD; Battle, PD
    Polycrystalline samples in the solid solution ZrMn2−xCoxGe4O12 (x = 0.0, 0.5, 1.0, 1.5 and 2.0) have been prepared using the ceramic method and characterised by a combination of magnetometry, X-ray diffraction and neutron diffraction. They all adopt the space group P4/nbm with a ∼ 9.60, c ∼ 4.82 Å and show long-range magnetic order with transition temperatures, TC, in the range 2 ≤ TC/K ≤ 10. The underlying magnetic structure is the same in each case but the ordered spins lie along [001] when x = 0.0 and in the (001) plane for all other compositions. In all cases the magnetically-ordered phase is a weak ferromagnet although the magnitude of the spontaneous magnetisation and the strength of the coercive field are composition-dependent. The magnetic structure can be rationalized by considering the strengths of the interactions along the distinct M–O–Ge–O–M superexchange pathways in the crystal and the observed magnetic structure is entirely consistent with the predictions of ab initio calculations. © The Royal Society of Chemistry 2017
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    The interplay of microstructure and magnetism in La3Ni2SbO9
    (Elsevier, 2014-12) Battle, PD; Avdeev, M; Hadermann, J
    La3Ni2SbO9 adopts a perovskite-related structure in which the six-coordinate cation sites are occupied alternately by Ni2+ and a disordered arrangement of Ni2+/Sb5+. A polycrystalline sample has been studied by neutron diffraction in applied magnetic fields of 0≤H/kOe≤50 at 5 K. In 0 kOe, weak magnetic Bragg scattering consistent with the adoption of a G-type ferrimagnetic structure is observed; the ordered component of the magnetic moment was found to be 0.89(7) µB per Ni2+ cation. This increased to 1.60(3) µB in a field of 50 kOe. Transmission electron microscopy revealed variations in the Ni:Sb ratio across crystallites of the sample. It is proposed that these composition variations disrupt the magnetic superexchange interactions within the compound, leading to domain formation and a reduced average moment. The application of a magnetic field aligns the magnetisation vectors across the crystal and the average moment measured by neutron diffraction increases accordingly. The role played by variations in the local chemical composition in determining the magnetic properties invites comparison with the behaviour of relaxor ferroelectrics. © 2014 Elsevier Inc.
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    Magnetic properties of CeM1.5M’0.5Ge4O12 (M = Mn, Co; M’ = Ni, Cu)
    (Elsevier, 2018-09-01) Xu, D; Avdeev, M; Battle, PD
    A study of the solid solutions CeM2-xM’xGe4O12 (M = Mn, Co; M’ = Ni, Cu) by X-ray diffraction and magnetometry is described. For M = Co the introduction of Ni and Cu was possible for x ≤ 0.5; for M = Mn attempts to introduce Cu were unsuccessful but CeMn1.5Ni0.5GeO4 was obtained as a single phase. These compositions crystallise in the space group P4/nbm with a ~9.76, c ~4.85 Å. They all order antiferromagnetically with TN< 10 K. The magnetic structures adopted by CeMn1.5Ni1.5Ge4O12 and CeCo1.5Cu0.5Ge4O12 were shown by neutron diffraction to be the same as those adopted by CeMn2Ge4O12 and CeCo2Ge4O12, respectively. The in-field metamagnetic transition of the latter to a weakly ferromagnetic phase was shown to persist in the Cu-doped composition. The available data suggest that the anisotropy associated with the Co2+ cation plays a dominant role in determining the magnetic behaviour of these compounds.© 2018 Elsevier Inc.
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    Magnetic properties of CeMn2–xCoxGe4O12 (0 ≤ x ≤ 2) as a function of temperature and magnetic field
    (American Chemical Society, 2017-02-15) Xu, D; Avdeev, M; Battle, PD; Liu, XQ
    Polycrystalline samples, prepared by a solid-state route, of compositions in the solid solution CeMn2–xCoxGe4O12 (x = 0.0, 0.5, 1.0, 1.5, and 2.0) were characterized by X-ray diffraction, neutron diffraction, and magnetometry. They adopt space group P4/nbm with a ≈ 9.78 and c ≈ 4.85 Å and become anti-ferromagnetic (x = 0.0, 1.5, 2.0) or weakly ferromagnetic (x = 0.5, 1.0) at 4.2 ≤ T ≤ 7.6 K. The ordered moments lie along [001] when x = 0.0 and in the (001) plane otherwise. The unit cell doubles along [001] when x = 1.5 and 2.0 order anti-ferromagnetically, but the doubling is lost when a first-order metamagnetic transition to weak ferromagnetism occurs on the application of a 10 kOe magnetic field. The ordered moments at 1.6 K for x = 0.0 and 2.0 are 4.61(2) and 2.58(2) μB, respectively; the corresponding effective moments in the paramagnetic phase are 5.91 and 5.36 μB. © 2017 American Chemical Society
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    Magnetic properties of La3Ni2SbxTayNb1–x–yO9; from relaxor to spin glass
    (Elsevier, 2019-05-01) Chin, CM; Battle, PD; Hunter, EC; Avdeev, M; Hendrickx, M; Hadermann, J
    Neutron diffraction experiments conducted at 5 K in a magnetic field 0 ≤ H/kOe ≤50 have shown that the monoclinic perovskite La3Ni2TaO9 behaves as a relaxor ferromagnet. Compositions in the series La3Ni2SbxTayNb1–x–yO9 have been synthesized in polycrystalline form. Electron microscopy, X–ray diffraction and neutron diffraction have shown that the solid solutions are largely homogeneous and monophasic. Magnetometry and neutron diffraction have shown that the relaxor magnetisation persists in low fields when x + y = 1 but is rapidly diminished by the introduction of niobium. This change in magnetic behaviour is ascribed to the differences in the d–orbital energies of Sb5+, Nb5+ and Ta5+. © 2019 The Authors CC BY licence. Published by Elsevier Inc.
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    Magnetic properties of Ln2CoGe4O12 and LnBCoGe4O12 (Ln = Gd, Tb, Dy, Ho, Er; B = Sc, Lu)
    (Royal Society of Chemistry, 2017-11-03) Xu, D; Avdeev, M; Battle, PD; Ryan, DH
    Polycrystalline samples of Ln2CoGe4O12 (Ln = Gd, Tb, Dy, Ho or Er) and LnBCoGe4O12 (B = Sc or Lu) have been prepared and characterised by a combination of magnetometry, 155Gd Mössbauer spectroscopy and, in the case of Tb2CoGe4O12 and TbScCoGe4O12, neutron diffraction. The holmium- and erbium-containing compositions remain paramagnetic down to 2 K, those containing dysprosium behave as spin glasses and the terbium and gadolinium-containing compounds show long-range magnetic order with transition temperatures below 4 K in all cases. The data can be rationalized qualitatively in terms of the interplay between magnetic anisotropy and crystal field effects. © Royal Society of Chemistry 2021
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    Magnetic properties of the 6H perovskite Ba3Fe2TeO9
    (Elsevier, 2017-09-01) Tang, YW; Paria Sena, R; Avdeev, M; Battle, PD; Cadogan, JM; Hadermann, J; Hunter, EC
    A 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.
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    Magnetisation reversal in Ca2PrCr2NbO9 and Ca2PrCr2TaO
    (Elsevier, 2019-01-01) Hunter, EC; Mousdale, S; Battle, PD; Avdeev, M
    Polycrystalline samples of the perovskites Ca2PrCr2BO9 (B = Nb, Ta) have been synthesised using the standard ceramic method and characterized by x-ray diffraction, neutron diffraction and magnetometry. Both crystallise in the orthorhombic space group Pnma and exhibit magnetisation reversal when field-cooled in an applied field of 100 Oe. The absolute value of the negative magnetisation at 2 K in an applied field of 100 Oe is an order of magnitude greater in Ca2PrCr2TaO9 than it is for Ca2PrCr2NbO9. Magnetometry and powder neutron diffraction showed that the Cr3+ cations in Ca2PrCr2NbO9 and Ca2PrCr2TaO9 order in a GyFz magnetic structure below 110 and 130 K, respectively. The Pr3+ cations remain paramagnetic down to ~ 10 K and show no-long range order at 2 K. Both compounds show a large degree of hysteresis in M(H), with coercive fields of 3.79 kOe and 3.03 kOe at 2 K. © 2018 The Authors. Opon Access CC BY licence. Published by Elsevier Inc.
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    Stabilisation of magnetic ordering in La3Ni2-xCuxB’O9 (B’= Sb, Ta, Nb) by the introduction of Cu2+
    (Elsevier, 2019-08-01) Chin, CM; Battle, PD; Hunter, EC; Avdeev, M; Hendrickx, M; Hadermann, J
    La3Ni2-xCuxB’O9 (x = 0.25; B’ = Sb, Ta, Nb: x = 0.5; B’ = Nb) have been synthesized and characterised by transmission electron microscopy, neutron diffraction and magnetometry. Each adopts a perovskite-like structure (space group P21/n) with two crystallographically-distinct six-coordinate sites, one occupied by a disordered arrangement of Ni2+ and Cu2+ and the other by a disordered ∼1:2 distribution of Ni2+ and B′5+, although some Cu2+ is found on the latter site when x = 0.5. Each composition undergoes a magnetic transition in the range 90 ≤ T/K ≤ 130 and shows a spontaneous magnetisation at 5 K; the transition temperature always exceeds that of the x = 0 composition by ≥ 30 K. A long-range ordered G-type ferrimagnetic structure is present in each composition, but small relaxor domains are also present. This contrasts with the pure relaxor and spin-glass behaviour of x = 0, B’ = Ta, Nb, respectively. © 2019 The Authors. This is an open access article under the CC BY license. Published by Elsevier Inc.
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    Structural chemistry and magnetic properties of LnMnFeGe4O12 (Ln = Y, Eu, Lu)
    (Elsevier, 2017-10-01) Xu, D; Avdeev, M; Battle, PD; Cadogan, JM; Lamont, H
    Polycrystalline samples of LnMnFeGe4O12 (Ln = Y, Eu, Lu) have been prepared using the ceramic method and characterised by a combination of magnetometry, Mössbauer spectroscopy, X-ray diffraction and neutron diffraction. They all adopt the space group P4/nbm with a ~ 9.670, c ~ 4.81 Å and show long-range antiferromagnetic order with transition temperatures 15 ≤ TN/K ≤ 17. The magnetic structure is the same in each case and consists of an A-type ordering of (001) planes; the ordered spins lie in the (001) plane. Comparison with isostructural compounds leads to the conclusion that subtle structural changes play a greater role than the electronic configuration of the cation in determining the magnetic structure. © 2017 Elsevier Inc.
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    Structural chemistry and magnetic properties of the perovskite Sr3Fe2TeO
    (Elsevier, 2016-06-29) Tang, YW; Hunter, EC; Battle, PD; Paria Sena, R; Hadermann, J; Avdeev, M; Cadogan, JM
    A polycrystalline sample of perovskite-like Sr3Fe2TeO9 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. The majority of the reaction product is shown to be a trigonal phase with a 2:1 ordered arrangement of Fe3+ and Te6+ cations. However, the sample is prone to nano-twinning and tetragonal domains with a different pattern of cation ordering exist within many crystallites. Antiferromagnetic ordering exists in the trigonal phase at 300 K and Sr3Fe2TeO9 is thus the first example of a perovskite with 2:1 trigonal cation ordering to show long-range magnetic order. At 300 K the antiferromagnetic phase coexists with two paramagnetic phases which show spin-glass behaviour below ~80 K. © 2016 The Authors. Published by Elsevier Inc. This is an open access article under the CC BY license