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Vasilakaki, M., Ntallis, N., Bellusci, M., Varsano, F., Mathieu, R., Fiorani, D., . . . Trohidou, K. N. (2020). Effect of albumin mediated clustering on the magnetic behavior of MnFe2O4 nanoparticles: experimental and theoretical modeling study. Nanotechnology, 31(2), Article ID 025707.
Open this publication in new window or tab >>Effect of albumin mediated clustering on the magnetic behavior of MnFe2O4 nanoparticles: experimental and theoretical modeling study
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2020 (English)In: Nanotechnology, ISSN 0957-4484, E-ISSN 1361-6528, Vol. 31, no 2, article id 025707Article in journal (Refereed) Published
Abstract [en]

Over the last two decades, iron oxide based nanoparticles ferrofluids have attracted significant attention for a wide range of applications. For the successful use of these materials in biotechnology and energy, surface coating and specific functionalization is critical to achieve high dispersibility and colloidal stability of the nanoparticles in the ferrofluids. In view of this, the magnetic behavior of clusters of ultra-small MnFe2O4 nanoparticles covered by bovine serum albumin, which is known as a highly biocompatible and environmentally friendly surfactant, is investigated by magnetization measurements, and numerical simulations at an atomic and mesoscopic scale. The coating process with albumin produces a change in the structure, actual size and shape distribution of clusters of exchange coupled particles, giving rise to a distribution of blocking temperatures. The coated system exhibits a superspin glass (SSG) behavior with the SSG freezing temperatures similar to the uncoated ones, providing evidence that the strength of the dipolar interactions is not affected by the presence of the albumin. The DFT calculations show that the albumin coating reduces the surface anisotropy and the saturation magnetization in the nanoparticles leading to lower values of the coercive field in agreement with the experimental findings. Our results clearly demonstrate that the albumin coated clusters of MnFe2O4 particles are ideal systems for energy and biomedical applications since colloidal and thermal stability as well as biosafety is obtained through the albumin coating.

Keywords
magnetic nanoparticles, albumin coating, ab initio calculations, Monte Carlo simulation
National Category
Physical Chemistry Nano Technology
Identifiers
urn:nbn:se:uu:diva-402630 (URN)10.1088/1361-6528/ab4764 (DOI)000504908900007 ()31603864 (PubMedID)
Available from: 2020-01-17 Created: 2020-01-17 Last updated: 2020-01-17Bibliographically approved
Sanchez, E. H., Vasilakaki, M., Lee, S. S., Normile, P. S., Muscas, G., Murgia, M., . . . De Toro, J. A. (2020). Simultaneous Individual and Dipolar Collective Properties in Binary Assemblies of Magnetic Nanoparticles. Chemistry of Materials, 32(3), 969-981
Open this publication in new window or tab >>Simultaneous Individual and Dipolar Collective Properties in Binary Assemblies of Magnetic Nanoparticles
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2020 (English)In: Chemistry of Materials, ISSN 0897-4756, E-ISSN 1520-5002, Vol. 32, no 3, p. 969-981Article in journal (Refereed) Published
Abstract [en]

Applications based on aggregates of magnetic nanoparticles are becoming increasingly widespread, ranging from hyperthermia to magnetic recording. However, although some uses require collective behavior, others need a more individual-like response, the conditions leading to either of these behaviors are still poorly understood. Here, we use nanoscale-uniform binary random dense mixtures with different proportions of oxide magnetic nanoparticles with low/high anisotropy as a valuable tool to explore the crossover from individual to collective behavior. Two different anisotropy scenarios have been studied in two series of binary compacts: M1, comprising maghemite (gamma-Fe2O3) nanoparticles of different sizes (9.0 nm/11.5 nm) with barely a factor of 2 between their anisotropy energies, and M2, mixing equally sized pure maghemite (low-anisotropy) and Co-doped maghemite (high-anisotropy) nanoparticles with a large difference in anisotropy energy (ratio > 8). Interestingly, while the M1 series exhibits collective behavior typical of strongly coupled dipolar systems, the M2 series presents a more complex scenario where different magnetic properties resemble either "individual-like" or "collective", crucially emphasizing that the collective character must be ascribed to specific properties and not to the system as a whole. The strong differences between the two series offer new insight (systematically ratified by simulations) into the subtle interplay between dipolar interactions, local anisotropy and sample heterogeneity to determine the behavior of dense assemblies of magnetic nanoparticles.

Place, publisher, year, edition, pages
AMER CHEMICAL SOC, 2020
National Category
Condensed Matter Physics
Identifiers
urn:nbn:se:uu:diva-407623 (URN)10.1021/acs.chemmater.9b03268 (DOI)000513299400004 ()
Funder
Swedish Research CouncilEU, Horizon 2020, 731976
Available from: 2020-03-31 Created: 2020-03-31 Last updated: 2020-03-31Bibliographically approved
Liu, L., Skogby, H., Ivanov, S., Weil, M., Mathieu, R. & Lazor, P. (2019). Bandgap engineering in Mn3TeO6: giant irreversible bandgap reduction triggered by pressure. Chemical Communications, 55(80), 12000-12003
Open this publication in new window or tab >>Bandgap engineering in Mn3TeO6: giant irreversible bandgap reduction triggered by pressure
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2019 (English)In: Chemical Communications, ISSN 1359-7345, E-ISSN 1364-548X, Vol. 55, no 80, p. 12000-12003Article in journal (Refereed) Published
Abstract [en]

In this study, the bandgap energy of the multiferroic oxide Mn3TeO6 is successfully reduced by similar to 39% from 3.15 eV to 1.86 eV, accompanied by a phase transition at high pressures. The high-pressure phase with smaller bandgap energy is quenchable to ambient conditions and represents a promising light-harvesting material for photovoltaic applications.

National Category
Physical Chemistry
Identifiers
urn:nbn:se:uu:diva-397942 (URN)10.1039/c9cc04821a (DOI)000496529500030 ()31524904 (PubMedID)
Funder
Swedish Research Council
Available from: 2020-01-02 Created: 2020-01-02 Last updated: 2020-01-02Bibliographically approved
Liu, L., Skogby, H., Ivanov, S., Weil, M., Mathieu, R. & Lazor, P. (2019). Bandgap engineering in Mn3TeO6: giant irreversible bandgap reduction triggered by pressure. Chemical Communications, 55, 12000
Open this publication in new window or tab >>Bandgap engineering in Mn3TeO6: giant irreversible bandgap reduction triggered by pressure
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2019 (English)In: Chemical Communications, ISSN 1359-7345, E-ISSN 1364-548X, Vol. 55, p. 12000-Article in journal (Refereed) Published
Abstract [en]

In this study, the bandgap energy of the multiferroic oxide Mn3TeO6 is successfully reduced by ∼39% from 3.15 eV to 1.86 eV, accompanied by a phase transition at high pressures. The high-pressure phase with smaller bandgap energy is quenchable to ambient conditions and represents a promising light-harvesting material for photovoltaic applications.

National Category
Condensed Matter Physics
Identifiers
urn:nbn:se:uu:diva-395737 (URN)10.1039/C9CC04821A (DOI)
Available from: 2019-10-23 Created: 2019-10-23 Last updated: 2020-02-07Bibliographically approved
Ivanov, S., Beran, P., Bush, A. A., Sarkar, T., Shafeie, S., Wang, D., . . . Mathieu, R. (2019). Cation ordering, ferrimagnetism and ferroelectric relaxor behavior in Pb(Fe1-xScx)(2/3)W1/3O3 solid solutions. European Physical Journal B: Condensed Matter Physics, 92(8), Article ID 163.
Open this publication in new window or tab >>Cation ordering, ferrimagnetism and ferroelectric relaxor behavior in Pb(Fe1-xScx)(2/3)W1/3O3 solid solutions
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2019 (English)In: European Physical Journal B: Condensed Matter Physics, ISSN 1434-6028, E-ISSN 1434-6036, Vol. 92, no 8, article id 163Article in journal (Refereed) Published
Abstract [en]

Ceramic samples of the multiferroic perovskite Pb(Fe1-xScx)(2/3)W1/3O3 with 0 <= x <= 0.4 have been synthesized using a conventional solid-state reaction method, and investigated experimentally and theoretically using first-principle calculations. Rietveld analyses of joint synchrotron X-ray and neutron diffraction patterns show the formation of a pure crystalline phase with cubic (Fm3(_)m) structure with partial ordering in the B-sites. The replacement of Fe by Sc leads to the increase of the cation order between the B and B '' sites. As the non-magnetic Sc3+ ions replace the magnetic Fe3+ cations, the antiferromagnetic state of PbFe2/3W1/3O3 is turned into a ferrimagnetic state reflecting the different magnitude of the magnetic moments on the B ' and B '' sites. The materials remain ferroelectric relaxors with increasing Sc content. Results from experiments on annealed and quenched samples show that the cooling rate after high temperature annealing controls the degree of cationic order in Pb(Fe1-xScx)(2/3)W1/3O3 and possibly also in the undoped PbFe2/3W1/3O3.

Place, publisher, year, edition, pages
SPRINGER, 2019
Keywords
Solid State and Materials
National Category
Condensed Matter Physics
Identifiers
urn:nbn:se:uu:diva-392576 (URN)10.1140/epjb/e2019-100149-9 (DOI)000477626500002 ()
Funder
Swedish Research Council
Available from: 2019-09-09 Created: 2019-09-09 Last updated: 2019-09-09Bibliographically approved
Sayed, F., Muscas, G., Jovanovic, S., Barucca, G., Locardi, F., Varvaro, G., . . . Sarkar, T. (2019). Controlling magnetic coupling in bi-magnetic nanocomposites. Nanoscale, 11(30), 14256-14265
Open this publication in new window or tab >>Controlling magnetic coupling in bi-magnetic nanocomposites
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2019 (English)In: Nanoscale, ISSN 2040-3364, E-ISSN 2040-3372, Vol. 11, no 30, p. 14256-14265Article in journal (Refereed) Published
Abstract [en]

Magnetic nanocomposites constitute a vital class of technologically relevant materials, in particular for next-generation applications ranging from biomedicine, catalysis, and energy devices. Key to designing such materials is determining and controlling the extent of magnetic coupling in them. In this work, we show how the magnetic coupling in bi-magnetic nanocomposites can be controlled by the growth technique. Using four different synthesis strategies to prepare prototypical LaFeO3-CoFe2O4 and LaFeO3-Co0.5Zn0.5Fe2O4 nanocomposite systems, and by performing comprehensive magnetic measurements, we demonstrate that the final material exhibits striking differences in their magnetic coupling that is distinct to the growth method. Through structural and morphological studies, we confirm the link between the magnetic coupling and growth methods due to distinct levels of particle agglomeration at the very microscopic scale. Our studies reveal an inverse relationship between the strength of magnetic coupling and the degree of particle agglomeration in the nanocomposites. Our work presents a basic concept of controlling the particle agglomeration to tune magnetic coupling, relevant for designing advanced bi-magnetic nanocomposites for novel applications.

Place, publisher, year, edition, pages
Royal Society of Chemistry, 2019
National Category
Physical Chemistry
Identifiers
urn:nbn:se:uu:diva-394637 (URN)10.1039/c9nr05364f (DOI)000484234700021 ()31318002 (PubMedID)
Funder
Swedish Research Council, 2017-05030Swedish Research Council, 188-0179Carl Tryggers foundation , KF 17:18
Available from: 2019-10-17 Created: 2019-10-17 Last updated: 2019-10-17Bibliographically approved
Joshi, D. C., Nordblad, P. & Mathieu, R. (2019). Ferromagnetic excess moments and apparent exchange bias in FeF2 single crystals. Scientific Reports, 9, Article ID 18884.
Open this publication in new window or tab >>Ferromagnetic excess moments and apparent exchange bias in FeF2 single crystals
2019 (English)In: Scientific Reports, ISSN 2045-2322, E-ISSN 2045-2322, Vol. 9, article id 18884Article in journal (Refereed) Published
Abstract [en]

The anisotropic antiferromagnet FeF2 has been extensively used as an antiferromagnetic layer to induce exchange bias effects in ferromagnetic/antiferromagnetic bilayers and heterostructures. In this work, an apparent exchange bias occurring in the low temperature hysteresis loops of FeF2 single crystals is investigated. A detailed investigation of the hysteresis and remnant magnetization indicates that the observation of an apparent exchange bias in FeF2 stems from an intrinsic excess moment associated with a distortion of the antiferromagnetic structure of piezomagnetic origin.

Place, publisher, year, edition, pages
NATURE PUBLISHING GROUP, 2019
National Category
Condensed Matter Physics
Identifiers
urn:nbn:se:uu:diva-402224 (URN)10.1038/s41598-019-55142-6 (DOI)000502616700001 ()31827163 (PubMedID)
Funder
Swedish Research Council
Available from: 2020-01-17 Created: 2020-01-17 Last updated: 2020-01-17Bibliographically approved
Cedervall, J., Ivanov, S. A., Lewin, E., Beran, P., Andersson, M. S., Faske, T., . . . Mathieu, R. (2019). On the structural and magnetic properties of the double perovskite Nd2NiMnO6. Journal of materials science. Materials in electronics, 30(17), 16571-16578
Open this publication in new window or tab >>On the structural and magnetic properties of the double perovskite Nd2NiMnO6
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2019 (English)In: Journal of materials science. Materials in electronics, ISSN 0957-4522, E-ISSN 1573-482X, Vol. 30, no 17, p. 16571-16578Article in journal (Refereed) Published
Abstract [en]

The structural, electronic and magnetic properties of phase pure and stoichiometric samples of the double perovskite Nd2NiMnO6. Photoectron spectroscopy revels a mixed valence of the transition metal sites where Ni has 3+/2+ oxidation states and Mn has 3+/4+. The compound orders ferromagnetically at 195 K. The magnetic structure was determined from the refinement of the neutron diffraction data. The results suggests that the B-site magnetic moments align along the crystallographic a-direction.

Place, publisher, year, edition, pages
SPRINGER, 2019
National Category
Condensed Matter Physics
Identifiers
urn:nbn:se:uu:diva-395325 (URN)10.1007/s10854-019-02035-z (DOI)000486022200078 ()
Funder
Swedish Research Council
Available from: 2019-10-17 Created: 2019-10-17 Last updated: 2019-10-17Bibliographically approved
Pal, S., Jana, S., Govinda, S., Pal, B., Mukherjee, S., Keshavarz, S., . . . Sarma, D. D. (2019). Peculiar magnetic states in the double perovskite Nd2NiMnO6. Physical Review B, 100(4), Article ID 045122.
Open this publication in new window or tab >>Peculiar magnetic states in the double perovskite Nd2NiMnO6
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2019 (English)In: Physical Review B, ISSN 2469-9950, E-ISSN 2469-9969, Vol. 100, no 4, article id 045122Article in journal (Refereed) Published
Abstract [en]

We present magnetic measurements on Nd2NiMnO6 which exhibits a well-known insulating paramagnetic state to an insulating ferromagnetic state transition when cooled below 200 K. Beyond this basic fact, there is a great deal of diversity in the reported magnetic properties and interpretation of specific anomalies observed in the magnetic data of this compound below the Curie temperature. We address specifically two anomalies discussed in the past, namely, a spin-glass like behavior observed in some samples near 100 K and a downturn in the magnetization with a lowering of the temperature below approximately 50 K. We show for the first time that the application of an increasing magnetic field can systematically change the low-temperature behavior to make the down-turn in the magnetization into an upturn. With the help of first principle calculations and extensive simulations along with our experimental observations, we provide a microscopic understanding of all magnetic properties observed in this interesting system to point out that the glassiness around 100 K is absent in well-ordered samples and that the low-temperature magnetic anomaly below 50 K is a consequence of a ferromagnetic coupling of the Nd spin moments with the spin of the Ni-Mn ordered sublattice without giving rise to any ordering of the Nd sublattice that remains paramagnetic, contrary to earlier claims. We explain this counter-intuitive interpretation of a ferromagnetic coupling of Nd spins with Ni-Mn spin giving rise to a decrease in the total magnetic moment by noting the less than half-filled 4f occupation of Nd that ensures orbital and spin moments of Nd to be opposite to each other due to the spin-orbit coupling. Since the ground state total magnetic moment of Nd has a contribution from the orbital moment, that is larger than the spin moment, the total moment of Nd is indeed pointing in a direction opposite to the direction of spin moments of the Ni-Mn sublattice as a consequence of the ferromagnetic exchange coupling between Nd and Ni-Mn spins.

Place, publisher, year, edition, pages
AMER PHYSICAL SOC, 2019
National Category
Condensed Matter Physics
Identifiers
urn:nbn:se:uu:diva-391944 (URN)10.1103/PhysRevB.100.045122 (DOI)000476687000002 ()
Funder
Swedish Research Council, P46561-1Swedish Research Council, 2016-04524Swedish Research Council, 2013-08316Swedish Foundation for Strategic Research Knut and Alice Wallenberg FoundationeSSENCE - An eScience CollaborationStandUp
Available from: 2019-08-29 Created: 2019-08-29 Last updated: 2019-08-29Bibliographically approved
Liu, L., Ivanov, S., Mathieu, R., Weil, M., Li, X. & Lazor, P. (2019). Pressure tuning of octahedral tilt in the ordered double perovskite Pb2CoTeO6. Journal of Alloys and Compounds, 801, 310-317
Open this publication in new window or tab >>Pressure tuning of octahedral tilt in the ordered double perovskite Pb2CoTeO6
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2019 (English)In: Journal of Alloys and Compounds, ISSN 0925-8388, E-ISSN 1873-4669, Vol. 801, p. 310-317Article in journal (Refereed) Published
Abstract [en]

Double perovskites represent a family of materials with promising fundamental properties (e.g. multiferroicity) and vast potential applications. However, the knowledge of pressure effects on the crystal structure of double perovskite is limited, which hinders their efficient synthesis using high-pressure techniques. Pb2CoTeO6 (PCTO) is considered as a good candidate for multiferroic materials, although a polymorph with a polar structure has not been synthesized yet. In the present study, the pressure effect on the crystal structure of PCTO was systematically studied by employing in situ synchrotron X-ray powder diffraction and Raman scattering techniques up to 60 GPa. A structural phase transition from R-3 to I2/m structure was observed at around 20 GPa, indicating that increasing the pressure has a similar effect on PCTO as decreasing the temperature, i.e., promoting the distortion of the structure. No polar structure of PCTO has been observed in the applied pressure range. The present study provides a valuable information about the crystal structure evolution of double perovskites upon compression, and will benefit high-pressure syntheses of novel double perovskites in the future. 

Place, publisher, year, edition, pages
ELSEVIER SCIENCE SA, 2019
Keywords
Double perovskite, Phase transition, High pressure, Raman spectroscopy, X-ray powder diffraction
National Category
Materials Chemistry
Identifiers
urn:nbn:se:uu:diva-390373 (URN)10.1016/j.jallcom.2019.06.096 (DOI)000474352000039 ()
Funder
Swedish Research Council
Available from: 2019-08-12 Created: 2019-08-12 Last updated: 2019-11-25Bibliographically approved
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Identifiers
ORCID iD: ORCID iD iconorcid.org/0000-0002-5261-2047

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