Browsing by Author "Hunter, EC"

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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 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 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