Browsing by Author "Hadermann, J"

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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 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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    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