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Publications (10 of 318) 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
Karmaker, P. C., Rahman, M. O., Dan, N. H., Liba, S. I., Nordblad, P. & Hoque, S. M. (2019). Characterization of Nd(Tb)-Fe-B-based exchange-spring nanocomposite magnets. Emerging Materials Research, 8(2), 153-165
Open this publication in new window or tab >>Characterization of Nd(Tb)-Fe-B-based exchange-spring nanocomposite magnets
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2019 (English)In: Emerging Materials Research, ISSN 2046-0147, E-ISSN 2046-0155, Vol. 8, no 2, p. 153-165Article in journal (Refereed) Published
Abstract [en]

The authors attempt to optimize for performance the composition of R2Fe14B/Fe3B-based hard nanocomposite alloys with R = neodymium (Nd) and terbium (Tb) by optimizing phases in order to develop hysteresis parameters such as maximum magnetization, coercivity and maximum energy product through variation in composition and heat treatment. The samples were prepared from arc-melted ingots of different compositions. The crystallization temperatures were obtained from the differential scanning calorimeter traces of the samples with the composition Nd(4-x)TbxFe(71)Co(5)Cu(0.5)Nb(1)B(18.5) (x = 0.0, 0.2, 0.4, 0.6, 0.8 and 1.0). Depending on their crystallization temperatures, the samples were annealed at 600, 625, 650, 675 and 700 degrees C for 10 min. Amorphosity and crystallization behavior were studied by X-ray diffraction using copper (Cu) K-alpha radiation (1.5418 angstrom). The Mossbauer spectra of all the samples were recorded at room temperature by using iron-57 (Fe-57) Mossbauer spectrometry in transmission geometry with a constant-acceleration spectrometer. Magnetic properties were determined by a vibrating-sample magnetometer in the as-cast and annealed conditions. Although the highest values of coercivity and remanent ratio were found to be 4.18 kOe and 0.72, respectively, for the sample of composition Nd3Tb1Fe71Co5Cu0.5Nb1B18.5 annealed at 650 degrees C with a higher concentration of terbium, the highest maximum energy product was determined to be 12.67 MGOe for the sample of Nd3.8Tb0.2Fe71Co5Cu0.5Nb1B18.5.

Place, publisher, year, edition, pages
ICE PUBLISHING, 2019
Keywords
amorphous, annealing, nanocomposites
National Category
Condensed Matter Physics
Identifiers
urn:nbn:se:uu:diva-390593 (URN)10.1680/jemmr.18.00046 (DOI)000473343600011 ()
Available from: 2019-08-13 Created: 2019-08-13 Last updated: 2019-08-13Bibliographically 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
Ek, G., Nedumkandathil, R., Johansson, R., Montero, J., Zlotea, C., Andersson, M., . . . Haussermann, U. (2019). Hydrogen induced structure and property changes in Eu3Si4. Journal of Solid State Chemistry, 277, 37-45
Open this publication in new window or tab >>Hydrogen induced structure and property changes in Eu3Si4
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2019 (English)In: Journal of Solid State Chemistry, ISSN 0022-4596, E-ISSN 1095-726X, Vol. 277, p. 37-45Article in journal (Refereed) Published
Abstract [en]

Hydrides Eu3Si4H2-X were obtained by exposing the Zintl phase Eu3Si4 to a hydrogen atmosphere at a pressure of 30 bar and temperatures from 25 to 300 degrees C. Structural analysis using powder X-ray diffraction (PXRD) data suggested that hydrogenations in a temperature range 25-200 degrees C afford a uniform hydride phase with an orthorhombic structure (Immm, a approximate to 4.40 angstrom, b approximate to 3.97 angstrom, c approximate to 19.8 angstrom), whereas at 300 degrees C mixtures of two orthorhombic phases with c approximate to 19.86 and approximate to 19.58 angstrom were obtained. The assignment of a composition Eu3Si4H2+x is based on first principles DFT calculations, which indicated a distinct crystallographic site for H in the Eu3Si4 structure. In this position, H atoms are coordinated in a tetrahedral fashion by Eu atoms. The resulting hydride Eu3Si4H2 is stable by -0.46 eV/H atom with respect to Eu3Si4 and gaseous H-2. Deviations between the lattice parameters of the DFT optimized Eu3Si4H2 structure and the ones extracted from PXRD patterns pointed to the presence of additional H in interstitials also involving Si atoms. Subsequent DFT modeling of compositions Eu3Si4H3 and Eu3Si4H4 showed considerably better agreement to the experimental unit cell volumes. It was then concluded that the hydrides of Eu3Si4 have a composition Eu3Si4H2+x (x < 2) and are disordered with respect to H in Si2Eu3 interstitials. Eu3Si4 is a ferromagnet with a Tc at about 120 K. Ferromagnetism is effectively quenched in Eu3Si4H2+x. The effective magnetic moment for both materials is 7.5 pg which is typical for compounds containing Eu2+ 4f(7) ions.

Keywords
Zintl phases, Zintl phase hydrides, Rare earth metal silicides, Magnetic properties
National Category
Materials Chemistry
Identifiers
urn:nbn:se:uu:diva-399023 (URN)10.1016/j.jssc.2019.05.033 (DOI)000481726300006 ()
Funder
Swedish Research CouncilNordForsk
Available from: 2019-12-13 Created: 2019-12-13 Last updated: 2019-12-13Bibliographically approved
Cedervall, J., Andersson, M. S., Iusan, D., Delczeg-Czirjak, E. K., Jansson, U., Nordblad, P. & Sahlberg, M. (2019). Magnetic and mechanical effects of Mn substitutions in AlFe2B2. Journal of Magnetism and Magnetic Materials, 482, 54-60
Open this publication in new window or tab >>Magnetic and mechanical effects of Mn substitutions in AlFe2B2
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2019 (English)In: Journal of Magnetism and Magnetic Materials, ISSN 0304-8853, E-ISSN 1873-4766, Vol. 482, p. 54-60Article in journal (Refereed) Published
Abstract [en]

The mechanical and magnetic properties of the newly discovered MAB-phase class of materials based upon AlFe2B2 were investigated. The samples were synthesised from stoichiometric amounts of all constituent elements. X-ray diffraction shows that the main phase is orthorhombic with an elongated b-axis, similar to AlFe2B2. The low hardness and visual inspection of the samples after deformation indicate that these compounds are deformed via a delamination process. When substituting iron in AlFe2B2 with manganese, the magnetism in the system goes from being ferro- to antiferromagnetic via a disordered ferrimagnetic phase exhibited by AlFeMnB2. Density functional theory calculations indicate a weakening of the magnetic interactions among the transitions metal ions as iron is substituted by manganese in AlFe2B2. The Mn-Mn exchange interactions in AlMn2B2 are found to be very small.

National Category
Inorganic Chemistry
Identifiers
urn:nbn:se:uu:diva-331787 (URN)10.1016/j.jmmm.2019.03.046 (DOI)000465553100010 ()
Funder
Swedish Research CouncilSwedish Energy Agency, 2017/11-55Swedish Energy Agency, 2018/1-34
Available from: 2017-10-19 Created: 2017-10-19 Last updated: 2019-06-14Bibliographically approved
Cedervall, J., Andersson, M., Delczeg-Czirjak, E. K., Iusan, D., Pereiro, M., Roy, P., . . . Deen, P. P. (2019). Magnetocaloric effect in Fe2P: Magnetic and phonon degrees of freedom. Physical Review B, 99(17), Article ID 174437.
Open this publication in new window or tab >>Magnetocaloric effect in Fe2P: Magnetic and phonon degrees of freedom
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2019 (English)In: Physical Review B, ISSN 2469-9950, E-ISSN 2469-9969, Vol. 99, no 17, article id 174437Article in journal (Refereed) Published
Abstract [en]

Devices based on magnetocaloric materials provide great hope for environmentally friendly and energy efficient cooling that does not rely on the use of harmful gasses. Fe2P based compounds are alloys that have shown great potential for magnetocaloric devices. The magnetic behavior in Fe2P is characterized by a strong magnetocaloric effect that coexists with a first-order magnetic transition (FOMT). Neutron diffraction and inelastic scattering, Mossbauer spectroscopy, and first-principles calculations have been used to determine the structural and magnetic state of Fe2P around the FOMT. The results reveal that ferromagnetic moments in the ordered phase are perturbed at the FOMT such that the moments cant away from the principle direction within a small temperature region. The acoustic-phonon modes reveal a temperature-dependent nonzero energy gap in the magnetically ordered phase that falls to zero at the FOMT. The interplay between the FOMT and the phonon energy gap indicates hybridization between magnetic modes strongly affected by spin-orbit coupling and phonon modes leading to magnon-phonon quasiparticles that drive the magnetocaloric effect.

National Category
Condensed Matter Physics
Identifiers
urn:nbn:se:uu:diva-387585 (URN)10.1103/PhysRevB.99.174437 (DOI)000469324500011 ()
Funder
Swedish Research CouncilSwedish Foundation for Strategic Research , EM16-0039
Available from: 2019-06-26 Created: 2019-06-26 Last updated: 2019-06-26Bibliographically 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
Joshi, D. C., Ivanov, S. A., Bush, A. A., Sarkar, T., Ye, Z.-G., Nordblad, P. & Mathieu, R. (2019). Room temperature ferrimagnetism in Yb-doped relaxor ferroelectric PbFe2/3W1/3O3. Applied Physics Letters, 115(7), Article ID 072902.
Open this publication in new window or tab >>Room temperature ferrimagnetism in Yb-doped relaxor ferroelectric PbFe2/3W1/3O3
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2019 (English)In: Applied Physics Letters, ISSN 0003-6951, E-ISSN 1077-3118, Vol. 115, no 7, article id 072902Article in journal (Refereed) Published
Abstract [en]

We report ferrimagnetism and reentrant relaxor ferroelectricity near room temperature in a Yb-doped PbFe2/3W1/3O3 cubic perovskite. Structural analysis reveals the presence of a single cubic perovskite phase, with the m space group [lattice parameter: a=8.0112(3) angstrom], and partial B-site ordering. The B-site ordering yields uncompensated magnetic moments in the antiferromagnetic structure of PbFe2/3W1/3O3 and ferrimagnetism near room temperature. An excess moment of similar to 0.6 mu(B)/B-site may be estimated from magnetic hysteresis curves recorded up to 50kOe at 5K. The temperature dependent magnetodielectric study reveals a sequential phase transition from a long-range ferroelectric state (across 280K) to a short-range relaxor ferroelectric state (across 190K). The long-range ferroelectric ordering is found to be more affected by the application of external magnetic fields than the relaxor phase.

Place, publisher, year, edition, pages
AMER INST PHYSICS, 2019
National Category
Condensed Matter Physics
Identifiers
urn:nbn:se:uu:diva-393740 (URN)10.1063/1.5112142 (DOI)000481469900044 ()
Funder
Swedish Research Council, 2017-05030Swedish Research Council
Available from: 2019-11-26 Created: 2019-11-26 Last updated: 2019-11-26Bibliographically 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
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ORCID iD: ORCID iD iconorcid.org/0000-0002-4561-9996

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