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Publications (10 of 107) Show all publications
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
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: 2019-08-12Bibliographically approved
Liu, L., Song, H. X., Li, X., Zhang, D., Mathieu, R., Ivanov, S., . . . Lazor, P. (2019). Pressure-induced polymorphism and piezochromism in Mn2FeSbO6. Applied Physics Letters, 114(16), Article ID 162903.
Open this publication in new window or tab >>Pressure-induced polymorphism and piezochromism in Mn2FeSbO6
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2019 (English)In: Applied Physics Letters, ISSN 0003-6951, E-ISSN 1077-3118, Vol. 114, no 16, article id 162903Article in journal (Refereed) Published
Abstract [en]

In the last decade, major efforts have been devoted to searching for polar magnets due to their vast potential applications in spintronic devices. However, the polar magnets are rare because of conflicting electronic configuration requirements of ferromagnetism and electric polarization. Double-perovskite oxides with a polar structure containing transition metal elements represent excellent candidates for the polar magnet design. Herein, the crystal structure evolution of Mn2FeSbO6 (MFSO) was investigated at pressures reaching similar to 50 GPa by in situ synchrotron X-ray diffraction (XRD), Raman scattering, and ab initio calculation techniques. The XRD results reveal ilmenite-to perovskite-type phase transition at around 35 GPa. An additional intermediate phase, observed in the range of 31-36 GPa by Raman spectroscopy, but not the XRD technique, is proposed to represent the polar LiNbO3 phase. It is argued that this phase emerged due to the heating effect of the Raman-excitation laser. The LiNbO3-type MFSO compounds, displaying an intrinsic dipole ordering, represent a promising candidate for multiferroic materials. The detected phase transitions were found to be reversible although a significant hysteresis was noticeable between compression and decompression runs. Moreover, a pressure-induced piezochromism, signifying a bandgap change, was discovered by the direct visual observations and corroborated by ab initio calculations. The present study benefits an efficient high-pressure synthesis of polar magnetic double-perovskite oxides in the future.

Place, publisher, year, edition, pages
AMER INST PHYSICS, 2019
National Category
Condensed Matter Physics
Identifiers
urn:nbn:se:uu:diva-383857 (URN)10.1063/1.5090649 (DOI)000466264600024 ()
Available from: 2019-05-24 Created: 2019-05-24 Last updated: 2019-05-24Bibliographically approved
Nag, A., Bhowal, S., Bert, F., Hillier, A. D., Itoh, M., Carlomagno, I., . . . Ray, S. (2018). Ba3MIr2O9 hexagonal perovskites in the light of spin-orbit coupling and local structural distortions. Physical Review B, 97(6), Article ID 064408.
Open this publication in new window or tab >>Ba3MIr2O9 hexagonal perovskites in the light of spin-orbit coupling and local structural distortions
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2018 (English)In: Physical Review B, ISSN 2469-9950, E-ISSN 2469-9969, Vol. 97, no 6, article id 064408Article in journal (Refereed) Published
Abstract [en]

Spin-orbit coupling (SOC) is found to be crucial for understanding themagnetic and electronic properties of 5d transitionmetal oxides. In 5d systems, with Ir5+ ions, where ideally a nonmagnetic J = 0 ground state is expected to be stabilized in the presence of strong SOC, often spontaneous moments are generated due to hopping induced superexchange. This effect is more pronounced when the Ir atoms are close by, as in systems with Ir2O9 dimers in 6H Ba3MIr2O9 compounds where magnetism is an outcome of complex Ir-O-Ir exchange paths, and is strongly influenced by the presence of local distortions. We find that subtle variations in the local structure of Ba3MIr2O9 (M = Mg, Sr, and Ca) lead to markedly differentmagnetic properties. While SOC plays a pivotal role in explaining the insulating ground states of these systems, it is seen that Ba3MgIr2O9, having a P6(3)/mmc symmetry, does not order down to low temperature despite having antiferromagnetic exchange interactions, while Ba3CaIr2O9 shows weak dimer-like features and stabilizes in C2/c' magnetic configuration with no net moment, and Ba3SrIr2O9 possesses a ground state corresponding to themagnetic space groupC2'/c' and exhibits ferromagnet-like features.

Place, publisher, year, edition, pages
AMER PHYSICAL SOC, 2018
National Category
Physical Sciences Engineering and Technology
Identifiers
urn:nbn:se:uu:diva-346659 (URN)10.1103/PhysRevB.97.064408 (DOI)000424744900010 ()
Available from: 2018-03-22 Created: 2018-03-22 Last updated: 2018-03-28Bibliographically approved
Akhter, S., Hakim, M. A., Hoque, S. M., Mathieu, R. & Nordblad, P. (2018). Glassy behavior of diluted Cu-Zn ferrites. Journal of Magnetism and Magnetic Materials, 452, 261-265
Open this publication in new window or tab >>Glassy behavior of diluted Cu-Zn ferrites
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2018 (English)In: Journal of Magnetism and Magnetic Materials, ISSN 0304-8853, E-ISSN 1873-4766, Vol. 452, p. 261-265Article in journal (Refereed) Published
Abstract [en]

The magnetic behavior of Zn substituted Cu-Zn spinel ferrites having chemical formula Cu1-xZnxFe2O4 (x = 0.7, 0.8, 0.9 and 1.0) has been studied by SQUID magnetometry, by means of magnetic hysteresis, field-cooled (FC) and zero-field-cooled (ZFC) magnetization, memory effect and low field ac susceptibility measurements. These measurements suggest that the ferrimagnetic phase of the x <= 0.8 samples is gradually turned into a spin glass (x >= 0.9). The compound with x = 0.9 exhibits the typical dynamical behavior of spin glasses, with indication of aging, rejuvenation and memory effects. The evolution of the magnetic properties of Cu-Zn spinel ferrites with substitution of Zn for Cu is discussed.

Place, publisher, year, edition, pages
ELSEVIER SCIENCE BV, 2018
Keywords
Ferrites, Reentrant spin glass, Spin glass, Memory effect, ac susceptibility
National Category
Condensed Matter Physics Engineering and Technology
Identifiers
urn:nbn:se:uu:diva-348826 (URN)10.1016/j.jmmm.2017.12.084 (DOI)000425547700039 ()
Available from: 2018-04-20 Created: 2018-04-20 Last updated: 2018-05-02Bibliographically approved
Ivanov, S., Sarkar, T., Bazuev, G. V., Kuznetsov, M. V., Nordblad, P. & Mathieu, R. (2018). Modification of the structure and magnetic properties of ceramic La2CoMnO6 with Ru doping. Journal of Alloys and Compounds, 752, 420-430
Open this publication in new window or tab >>Modification of the structure and magnetic properties of ceramic La2CoMnO6 with Ru doping
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2018 (English)In: Journal of Alloys and Compounds, ISSN 0925-8388, E-ISSN 1873-4669, Vol. 752, p. 420-430Article in journal (Refereed) Published
Abstract [en]

Effects of Ru doping on the structure and magnetic properties of La2CoMn1-xRuxO6 ceramics with different compositions (x = 0, 0.1, 0.2, 0.3, 0.5, 0.75, 1.0) have been investigated using a variety of complementary techniques (X-ray powder diffraction and photoelectron spectroscopy, electron microscopy, and magnetometry). Phase-pure polycrystalline samples were prepared by the conventional solid-state reaction method including high pressure (3000 kg/cm(2) ) treatment of the original mixture of reagents. X-ray diffraction analyses of the samples accompanied with Rietveld refinement suggested a change in the crystal structure upon doping: for 0 <= x <= 0.3 the structure of the samples is predominantly disordered orthorhombic (s.g. Pnma) which transformed to ordered monoclinic (s.g. P2(1)/n) for 0.5 <= x <= 1. This suggests that Ru doping induces (partial) cation order in the B-sublattice. Magnetic measurements indicated a low temperature ferromagnetic phase, and a positive value of the Curie-Weiss temperature (theta cw) was derived for all samples of composition x <= 0.75. However, the Curie temperature (T-c) and theta cw decreased with increasing Ru doping. These changes in Tc upon doping can be correlated to the changes in the nearest neighbor and next nearest neighbor exchange interactions. The sample with x =1 orders antiferromagnetically at approximately 25 K.

Place, publisher, year, edition, pages
ELSEVIER SCIENCE SA, 2018
Keywords
Ceramics, Electronic materials, X-ray diffraction, Crystal structure, Magnetic properties
National Category
Materials Chemistry Inorganic Chemistry Engineering and Technology
Identifiers
urn:nbn:se:uu:diva-356606 (URN)10.1016/j.jallcom.2018.04.164 (DOI)000432672300051 ()
Funder
Swedish Research Council
Available from: 2018-08-03 Created: 2018-08-03 Last updated: 2018-08-15Bibliographically approved
Vasilakaki, M., Margaris, G., Peddis, D., Mathieu, R., Yaacoub, N., Fiorani, D. & Trohidou, K. (2018). Monte Carlo study of the superspin glass behavior of interacting ultrasmall ferrimagnetic nanoparticles. Physical Review B, 97(9), Article ID 094413.
Open this publication in new window or tab >>Monte Carlo study of the superspin glass behavior of interacting ultrasmall ferrimagnetic nanoparticles
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2018 (English)In: Physical Review B, ISSN 2469-9950, E-ISSN 2469-9969, Vol. 97, no 9, article id 094413Article in journal (Refereed) Published
Abstract [en]

The magnetism of a dense assembly of ultrasmall ferrimagnetic nanoparticles exhibits unique features due to the combination of intraparticle and strong interparticle interactions. To model such system we need to account for the internal particle structure and the short-and long-range interparticle interactions. We have developed a mesoscopic model for the particle assembly that includes three spins (two for the surface and one for the core) for the description of each nanoparticle, interparticle dipolar interactions and the interparticle exchange interactions for the nanoparticles in contact. The temperature dependence of the observed exchange bias effect, due to exchange coupling at the interface between core/surface spins and the interparticle exchange coupling, and the zero-field-cooled-field-cooled magnetization vs temperature curves have been investigated using the Monte Carlo simulation technique with the implementation of the Metropolis algorithm. Our simulations reproduce well the experimental data of ultrasmall similar to 2-nm MnFe2O4 nanoparticles, confirming the close relationship between the superspin glass state and the exchange-bias effect in dense nanoparticle systems, owing to the interplay between the intraparticle structure and the interparticle effects.

Place, publisher, year, edition, pages
AMER PHYSICAL SOC, 2018
National Category
Condensed Matter Physics Engineering and Technology
Identifiers
urn:nbn:se:uu:diva-350746 (URN)10.1103/PhysRevB.97.094413 (DOI)000427353800004 ()
Available from: 2018-05-16 Created: 2018-05-16 Last updated: 2018-06-05Bibliographically approved
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ORCID iD: ORCID iD iconorcid.org/0000-0002-5261-2047

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