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- Hausmann, Simon, et al.
(author)
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Atomic-scale engineering of ferroelectric-ferromagnetic interfaces of epitaxial perovskite films for functional properties
- 2017
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In: Scientific Reports. - : NATURE PUBLISHING GROUP. - 2045-2322. ; 7
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Journal article (peer-reviewed)abstract
- Besides epitaxial mismatch that can be accommodated by lattice distortions and/or octahedral rotations, ferroelectric-ferromagnetic interfaces are affected by symmetry mismatch and subsequent magnetic ordering. Here, we have investigated La-0.67 Sr-0.33 MnO3 (LSMO) samples with varying underlying unit cells (uc) of BaTiO3 (BTO) layer on (001) and (110) oriented substrates in order to elucidate the role of symmetry mismatch. Lattice mismatch for 3 uc of BTO and symmetry mismatch for 10 uc of BTO, both associated with local MnO6 octahedral distortions of the (001) LSMO within the first few uc, are revealed by scanning transmission electron microscopy. Interestingly, we find exchange bias along the in-plane [110]/[100] directions only for the (001) oriented samples. Polarized neutron reflectivity measurements confirm the existence of a layer with zero net moment only within (001) oriented samples. First principle density functional calculations show that even though the bulk ground state of LSMO is ferromagnetic, a large lattice constant together with an excess of La can stabilize an antiferromagnetic LaMnO3-type phase at the interface region and explain the experimentally observed exchange bias. Atomic scale tuning of MnO6 octahedra can thus be made possible via symmetry mismatch at heteroepitaxial interfaces. This aspect can act as a vital parameter for structure-driven control of physical properties.
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| 4. |
- Makarova, Tatiana L, et al.
(author)
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Magnetic Carbon
- 2001
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In: Nature. - : Springer Science and Business Media LLC. - 0028-0836 .- 1476-4687. ; 413:6857, s. 716-718
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Journal article (peer-reviewed)abstract
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| 5. |
- Paul, Amitesh, et al.
(author)
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Exotic exchange bias at epitaxial ferroelectric-ferromagnetic interfaces
- 2014
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In: Applied Physics Letters. - : AIP Publishing. - 0003-6951 .- 1077-3118. ; 105:2, s. 022409-
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Journal article (peer-reviewed)abstract
- Multiferroics in spintronics have opened up opportunities for future technological developments, particularly in the field of ferroelectric (FE)-ferromagnetic (FM) oxide interfaces with functionalities. We find strong exchange bias shifts (up to 84 Oe) upon field cooling in metal-oxide (Fe/BaTiO3) films combining- FM and FE layers. The saturation magnetic moment of the FM layer is also significantly higher than in hulk (3.0 +/- 0.2 mu(B)/atom) and the reversal mechanism occurs via a domain nucleation process. X-ray absorption spectroscopy at the Fe K-edge and Ba L3-edge indicate presence of few monolayers of antiferromagnetic FeO at the interface without the formation of any BaFeO3 layer. Polarized neutron reflectometry corroborates with our magnetization data as we perform depth profiling of the magnetic and structural densities in these bilayers. Our first principles density functional calculations support the formation of antiferromagnetic FeO layers at the interface along with an enhancement of Fe magnetic moments in the inner ferromagnetic layers. (C) 2014 AIP Publishing LLC.
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- Paul, Amitesh, et al.
(author)
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Structural, electronic and magnetic properties of YMnO3/La0.7Sr0.3MnO3 heterostructures
- 2014
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In: Journal of applied crystallography. - 0021-8898 .- 1600-5767. ; 47, s. 1054-1064
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Journal article (peer-reviewed)abstract
- Heterostructures with competing magnetic interactions are often exploited for their tailored new functionalities. Exchange bias is one such outcome of interfacial coupling across ferromagnetic-antiferromagnetic, multiferroic-ferromagnetic, two antiferromagnetic, or antiferromagnetic and paramagnetic interfaces. Apart from the usual horizontal shift of the hysteresis loop (exchange bias shift), a small 'vertical shift' of the hysteresis loops along the magnetization axis has also been seen, but it was always relatively small. Recently, an unusually large 'vertical shift' in epitaxial bilayer heterostructures comprising ferromagnetic La0.7Sr0.3MnO3 and multiferroic orthorhombic YMnO3 layers was reported. Here, using polarized neutron reflectometry, the magnetic proximity effect in such bilayers has been investigated. A detailed magnetic depth profile at the interface, elucidating the intrinsic nature of the vertical shift in such heterostructures, is reported. Further corroboration of this observation has been made by means of first-principles calculations, and the structural and electronic properties of YMnO3/La0.7Sr0.3MnO3 heterostructures are studied. Although in the bulk, the ground state of YMnO3 is an E-type antiferromagnet, the YMnO3/La0.7Sr0.3MnO3 heterostructure stabilizes the ferromagnetic phase in YMnO3 in the interface region. It is found that, in the hypothetical ferromagnetic phase of bulk YMnO3, the polarization is suppressed, and owing to a large difference between the lattice constants in the ab plane a strong magnetocrystalline anisotropy is present. This anisotropy produces a high coercivity of the unusual ferromagnetic YMnO3 phase at the interface, which is responsible for the large vertical shift observed in experiment. (C) 2014 International Union of Crystallography
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- Spemann, D., et al.
(author)
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Evidence for intrinsic weak ferromagnetism in a C60 polymer by PIXE and MFM
- 2003
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In: NUCLEAR INSTRUMENTS & METHODS IN PHYSICS RESEARCH SECTION B-BEAM INTERACTIONS WITH MATERIALS AND ATOMS. - Amsterdam : Elsevier. ; , s. 531-536
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Conference paper (peer-reviewed)abstract
- In this study a C60 polymer has been characterized for the first time with respect to impurity content and ferromagnetic properties by laterally resolved particle induced X-ray emission (PIXE) and magnetic force microscopy (MFM) in order to prove the existence of intrinsic ferromagnetism in this material. In the sample studied the main ferromagnetic impurity found was iron with an average concentration of 175 ± 16 μg/g within the sample volume probed by the ion beam. However, the Fe distribution is very inhomogeneous and characterized by micrometer-large impurity grains of almost pure iron surrounded by an almost pure carbon matrix. With MFM, the ferromagnetic properties have been investigated both in pure and contaminated regions of the sample as determined by PIXE. We found that ∼ 30% of the area of pure regions (concentration of magnetic impurities <1 μg/g) is characterized by ferromagnetic domains, which are partly correlated to grains and grain boundaries. These magnetic domains are of intrinsic origin and not related to impurities. In contaminated regions of the sample the ferromagnetic properties are dominated by the impurities as expected from the high impurity concentrations. The combination of PIXE and MFM allowed us to separate between the intrinsic and extrinsic magnetic regions and to directly prove that intrinsic ferromagnetism exists in a C60 polymer.
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- Talyzin, Alexandr, et al.
(author)
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Structural and magnetic properties of polymerized C60 with Fe
- 2007
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In: European Physical Journal B. - : Springer Science and Business Media LLC. - 1434-6028 .- 1434-6036. ; 55:1, s. 57-62
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Journal article (peer-reviewed)abstract
- We provide evidence that high-pressure high-temperature (2.5 GPa and 1040 K) treatment of mixtures of iron with fullerene powders leads to the complete transformation of iron into iron carbide Fe3C. The comparison of the magnetic properties (Curie temperature and magnetic moment) of the here studied samples and those for the ferromagnetic polymer Rh-C-60 indicates that the main ferromagnetic signal reported in those samples is due to Fe3C and not related to the ferromagnetism of carbon as originally interpreted. Taking into account the results obtained in this study the original paper on "Magnetic carbon" [Nature 413, 716 (2001)] was recently retracted.
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