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Jana, S., Panda, S. K., Phuyal, D., Pal, B., Mukherjee, S., Dutta, A., . . . Sarma, D. D. (2019). Charge disproportionate antiferromagnetism at the verge of the insulator-metal transition in doped LaFeO3. Physical Review B, 99(7), Article ID 075106.
Open this publication in new window or tab >>Charge disproportionate antiferromagnetism at the verge of the insulator-metal transition in doped LaFeO3
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2019 (English)In: Physical Review B, ISSN 2469-9950, E-ISSN 2469-9969, Vol. 99, no 7, article id 075106Article in journal (Refereed) Published
Abstract [en]

We explore the effects of electron doping in lanthanum ferrite, LaFeO3 by doping Mo at the Fe sites. Based on magnetic, transport, scanning tunneling spectroscopy, and x-ray photoelectron spectroscopy measurements, we find that the large gap, charge-transfer, antiferromagnetic (AFM) insulator LaFeO3 becomes a small gap AFM band insulator at low Mo doping. With increasing doping concentration, Mo states, which appear around the Fermi level, is broadened and become gapless at a critical doping of 20%. Using a combination of calculations based on density functional theory plus Hubbard U (DFT+U) and x-ray absorption spectroscopy measurements, we find that the system shows charge disproportionation (CD) in Fe ions at 25% Mo doping, where two distinct Fe sites, having Fe2+ and Fe3+ nominal charge states appear. A local breathing-type lattice distortion induces the charge disproportionation at the Fe site without destroying the antiferromagnetic order. Our combined experimental and theoretical investigations establish that the Fe states form a CD antiferromagnet at 25% Mo doping, which remains insulating, while the appearance of Mo states around the Fermi level is showing an indication towards the insulator-metal transition.

Place, publisher, year, edition, pages
AMER PHYSICAL SOC, 2019
National Category
Condensed Matter Physics
Identifiers
urn:nbn:se:uu:diva-378537 (URN)10.1103/PhysRevB.99.075106 (DOI)000458168300001 ()
Funder
Swedish Research Council, 2016-4524Knut and Alice Wallenberg Foundation, 2012.0031Swedish Energy Agency, P43294-1EU, European Research Council, CorrelMat-617196Swedish Research Council, 2016-03278Swedish Research CouncilSwedish Foundation for Strategic Research Carl Tryggers foundation , CTS-17:376eSSENCE - An eScience CollaborationStandUp
Available from: 2019-03-21 Created: 2019-03-21 Last updated: 2019-03-21Bibliographically approved
Fang, H., Li, J., Shafeie, S., Hedlund, D., Cedervall, J., Ekström, F., . . . Sahlberg, M. (2019). Insights into phase transitions and magnetism of MnBi crystals synthesized from self-flux. Journal of Alloys and Compounds, 781, 308-314
Open this publication in new window or tab >>Insights into phase transitions and magnetism of MnBi crystals synthesized from self-flux
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2019 (English)In: Journal of Alloys and Compounds, ISSN 0925-8388, E-ISSN 1873-4669, Vol. 781, p. 308-314Article in journal (Refereed) Published
Abstract [en]

To effectively synthesize high purity ferromagnetic low temperature phase (LTP) MnBi with optimal microstructure is still a challenge that needs to be overcome for the system to reach its full potential. Here, the phase transitions and magnetic properties of MnBi crystals are reported. The phase transition between the low and high temperature structure of MnBi was systematically investigated at different heating/cooling rates using in situ synchrotron radiation X-ray diffraction. The material crystallizes in a layered hexagonal structure giving a platelike microstructure. The magnetic characterization of the crystals reveal that the saturation magnetization varies from 645 kA/m at 50 K to 546 kA/m at 300 K. Magnetization measurements also show that the sample upon heating becomes non-magnetic and transforms to the high temperature phase (HTP) at similar to 640 K, and that it regains ferromagnetic properties and transforms back to the LTP at similar to 610 K upon subsequent cooling.

Place, publisher, year, edition, pages
ELSEVIER SCIENCE SA, 2019
Keywords
In situ synchrotron radiation X-ray diffraction, Phase transitions, Rare earth free permanent magnet, MnBi, Single crystals
National Category
Materials Chemistry
Identifiers
urn:nbn:se:uu:diva-378612 (URN)10.1016/j.jallcom.2018.12.146 (DOI)000457845900034 ()
Funder
Swedish Energy AgencySwedish Foundation for Strategic Research
Available from: 2019-03-11 Created: 2019-03-11 Last updated: 2019-03-13Bibliographically approved
Kontos, S., Fang, H., Li, J., Delczeg-Czirjak, E. K., Shafeie, S., Svedlindh, P., . . . Gunnarsson, K. (2019). Measured and calculated properties of B-doped τ-phase MnAl: A rare earth free permanent magnet. Journal of Magnetism and Magnetic Materials, 474, 591-598
Open this publication in new window or tab >>Measured and calculated properties of B-doped τ-phase MnAl: A rare earth free permanent magnet
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2019 (English)In: Journal of Magnetism and Magnetic Materials, Vol. 474, p. 591-598Article in journal (Refereed) Published
Abstract [en]

The metastable tetragonal τ-phase MnAl has been doped interstitially with B through a drop synthesis method creating the (Mn0.55Al0.45)B0.02 compound. The as-casted samples were annealed, quenched and thereafter ball-milled and relaxed in order to decrease grain size and reduce the number of crystallographic defects. The Curie temperature of the quenched sample was estimated to 655 K. The magnetization, coercivity and anisotropy were analyzed with respect to flash-milling time, relaxation time and temperature. The results show that (Mn0.55Al0.45)B0.02 could be directly obtained from drop synthesis. The highest measured saturation magnetization of 393 kA/m (measured at ±1440kA/m) was achieved with a relaxation process after 1.5h milling, giving a theoretical maximum energy product of 48 kJ/m3. The highest value of the coercivity was 355 kA/m achieved by flash-milling for 10 h. However, the high coercivity was achieved at an expense of low saturation magnetization.

Keywords
Permanent magnets; Rare-Earth-free; Diffraction; Magnetometry; Computational modeling
National Category
Condensed Matter Physics
Research subject
Physics
Identifiers
urn:nbn:se:uu:diva-368265 (URN)10.1016/j.jmmm.2018.11.006 (DOI)000459494600086 ()
Funder
Swedish Energy AgencySweGRIDS - Swedish Centre for Smart Grids and Energy Storage
Available from: 2018-12-03 Created: 2018-12-03 Last updated: 2019-03-21Bibliographically approved
Husain, S., Sisodia, N., Chaurasiya, A. K., Kumar, A., Singh, J. P., Yadav, B. S., . . . Chaudhary, S. (2019). Observation of Skyrmions at Room Temperature in Co2FeAl Heusler Alloy Ultrathin Film Heterostructures. Scientific Reports, 9, Article ID 1085.
Open this publication in new window or tab >>Observation of Skyrmions at Room Temperature in Co2FeAl Heusler Alloy Ultrathin Film Heterostructures
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2019 (English)In: Scientific Reports, ISSN 2045-2322, E-ISSN 2045-2322, Vol. 9, article id 1085Article in journal (Refereed) Published
Abstract [en]

Magnetic skyrmions are topological spin-textures having immense potential for energy efficient spintronic devices. Here, we report the observation of stable skyrmions in unpatterned Ta/Co2FeAl(CFA)/MgO thin film heterostructures at room temperature in remnant state employing magnetic force microscopy. It is shown that these skyrmions consisting of ultrathin ferromagnetic CFA Heusler alloy result from strong interfacial Dzyaloshinskii-Moriya interaction (i-DMI) as evidenced by Brillouin light scattering measurements, in agreement with the results of micromagnetic simulations. We also emphasize on room temperature observation of multiple skyrmions which can be stabilized for suitable combinations of CFA layer thickness, perpendicular magnetic anisotropy, and i-DMI. These results provide a significant step towards designing of room temperature spintronic devices based on skyrmions in full Heusler alloy based thin films.

National Category
Condensed Matter Physics
Identifiers
urn:nbn:se:uu:diva-377339 (URN)10.1038/s41598-018-35832-3 (DOI)000457287000073 ()30705297 (PubMedID)
Funder
Knut and Alice Wallenberg Foundation, KAW 2012.0031
Available from: 2019-02-22 Created: 2019-02-22 Last updated: 2019-02-22Bibliographically approved
Wetterskog, E., Jonasson, C., Smilgies, D.-M., Schaller, V., Johansson, C. & Svedlindh, P. (2018). Colossal Anisotropy of the Dynamic Magnetic Susceptibility in Low-Dimensional Nanocube Assemblies. ACS Nano, 12(2), 1403-1412
Open this publication in new window or tab >>Colossal Anisotropy of the Dynamic Magnetic Susceptibility in Low-Dimensional Nanocube Assemblies
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2018 (English)In: ACS Nano, ISSN 1936-0851, E-ISSN 1936-086X, Vol. 12, no 2, p. 1403-1412Article in journal (Refereed) Published
Abstract [en]

One of the ultimate goals of nanocrystal self-assembly is to transform nanoscale building blocks into a material that displays enhanced properties relative to the sum of its parts. Herein, we demonstrate that 1D needle shaped assemblies composed of Fe3-delta O4 nanocubes display a significant augmentation of the magnetic susceptibility and dissipation as compared to OD and 2D systems. The performance of the nanocube needles is highlighted by a colossal anisotropy factor defined as the ratio of the parallel to the perpendicular magnetization components. We show that the origin of this effect cannot be ascribed to shape anisotropy in its classical sense; as such, it has no analogy in bulk magnetic materials. The temperature-dependent anisotropy factors of the in- and out-of-phase components of the magnetization have an extremely strong particle size dependence and reach values of 80 and 2500, respectively, for the largest nanocubes in this study. Aided by simulations, we ascribe the anisotropy of the magnetic susceptibility, and its strong particle-size dependence to a synergistic coupling between the dipolar interaction field and a net anisotropy field resulting from a partial texture in the 1D nanocube needles.

Place, publisher, year, edition, pages
AMER CHEMICAL SOC, 2018
Keywords
magnetic properties, ac-susceptibility, anisotropy, magnetic nanoparticles, arrays, supercrystals, assemblies
National Category
Materials Chemistry Engineering and Technology
Identifiers
urn:nbn:se:uu:diva-351021 (URN)10.1021/acsnano.7b07745 (DOI)000426615600050 ()29328678 (PubMedID)
Funder
NIH (National Institute of Health), DMR-1332208
Available from: 2018-05-18 Created: 2018-05-18 Last updated: 2018-06-05Bibliographically approved
Frisk, A., Ali, H., Svedlindh, P., Leifer, K., Andersson, G. & Nyberg, T. (2018). Composition, structure and magnetic properties of ultra-thin Fe/Ni multilayers sputter deposited on epitaxial Cu/Si(001). Thin Solid Films, 646, 117-125
Open this publication in new window or tab >>Composition, structure and magnetic properties of ultra-thin Fe/Ni multilayers sputter deposited on epitaxial Cu/Si(001)
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2018 (English)In: Thin Solid Films, ISSN 0040-6090, E-ISSN 1879-2731, Vol. 646, p. 117-125Article in journal (Refereed) Published
Abstract [en]

Sputter deposited symmetric multilayers of (n Fe)/(n Ni), with individual thicknesses from n = 4 to n = 48 monolayers (ML), were deposited on epitaxial Cu/Si(001), and their microstructural evolution and magnetic properties versus n have been studied. Elemental layering can be seen with transmission electron microscopy down to n = 4 ML layer thickness, although an intermixed region characterized by a finite interface width is found to be present. This width is composed of the interface roughness as well as the interdiffusion between layers, but the relative contributions from these two sources could not be concluded by the techniques used. The measured elemental layering and X-ray reflectivity (XRR) give an upper limit to the interface width which must be smaller than the thinnest layers, 4 ML. Electron energy loss spectroscopy (EELS), depth profiling X-ray photoelectron spectroscopy (XPS) and also XRR reveal that Fe has a higher tendency to mix with Ni than vice versa. XPS does not have the resolution to measure this thin elemental layering: composition variations for n = 8 ML which are clearly seen by EELS are barely resolved by XPS. The structure was determined by X-ray diffraction, and an epitaxial fcc (001) structure is found to be maintained throughout the multilayers up to n less than or similar to 8 ML. For larger n values, relaxation starts by Fe-fcc(001) layers changing into Fe-bcc(110), which is then followed by Ni-fcc(001) changing from (001) to (111) orientation along the growth direction. A decreased total measured magnetic moment for the fully epitaxial multilayers can be explained by the fcc Fe layers being partly anti-ferromagnetic, whereas the relaxed multilayers exhibit the expected magnetic properties of (bcc Fe) +(fcc Ni).

National Category
Condensed Matter Physics Engineering and Technology
Identifiers
urn:nbn:se:uu:diva-305519 (URN)10.1016/j.tsf.2017.11.023 (DOI)000418575900017 ()
Funder
Swedish Research Council
Available from: 2016-10-22 Created: 2016-10-18 Last updated: 2018-02-27Bibliographically approved
Legaria, E. P., Saldan, I., Svedlindh, P., Wetterskog, E., Gunnarsson, K., Kessler, V. G. & Seisenbaeva, G. A. (2018). Coordination of rare earth element cations on the surface of silica-derived nanoadsorbents. Dalton Transactions, 47(4), 1312-1320
Open this publication in new window or tab >>Coordination of rare earth element cations on the surface of silica-derived nanoadsorbents
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2018 (English)In: Dalton Transactions, ISSN 1477-9226, E-ISSN 1477-9234, Vol. 47, no 4, p. 1312-1320Article in journal (Refereed) Published
Abstract [en]

Silica (SiO2)-derived nanoadsorbents are a powerful and attractive tool for the extraction and separation of rare earth elements (REE) from many perspectives such as reusability, efficiency and minimum impact on the environment. In the present work, we investigated two different methods of adsorption down to the molecular level: (1) the mechanism of the coordination of different groups of REE (light, medium, heavy) with iminodiacetic acid (IDA) was revealed by exploiting models obtained from X-ray crystallography, explaining the selectivity of this type of ligand, and (2) the mechanism of the seeding of RE(OH)(3) initiated by SiO2-based nanoadsorbents was investigated by EXAFS, both individually and in combination with mechanism (1), showing the coexistence of both mechanisms. The REE loaded nanoadsorbents possess a high magnetic susceptibility. This property was studied by magnetometry to quantify the REE adsorption efficiency and compared with the values obtained from complexometry.

Place, publisher, year, edition, pages
ROYAL SOC CHEMISTRY, 2018
National Category
Chemical Sciences Engineering and Technology
Identifiers
urn:nbn:se:uu:diva-346224 (URN)10.1039/c7dt04388k (DOI)000423465200036 ()29300064 (PubMedID)
Funder
EU, FP7, Seventh Framework Programme, 309373
Available from: 2018-03-15 Created: 2018-03-15 Last updated: 2018-03-28Bibliographically approved
Kumar, A., Wetterskog, E., Lewin, E., Tai, C.-W., Akansel, S., Husain, S., . . . Svedlindh, P. (2018). Effect of in situ electric-field-assisted growth on antiphase boundaries in epitaxial Fe3O4 thin films on MgO. Physical Review Materials, 2(5), Article ID 054407.
Open this publication in new window or tab >>Effect of in situ electric-field-assisted growth on antiphase boundaries in epitaxial Fe3O4 thin films on MgO
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2018 (English)In: Physical Review Materials, ISSN 2475-9953, Vol. 2, no 5, article id 054407Article in journal (Refereed) Published
Abstract [en]

Antiphase boundaries (APBs) normally form as a consequence of the initial growth conditions in all spinel ferrite thin films. These boundaries result from the intrinsic nucleation and growth mechanism, and are observed as regions where the periodicity of the crystalline lattice is disrupted. The presence of APBs in epitaxial films of the inverse spinel Fe3O4 alters their electronic and magnetic properties due to strong antiferromagnetic (AF) interactions across these boundaries. We explore the effect of using in-plane in situ electric-field-assisted growth on the formation of APBs in heteroepitaxial Fe3O4(100)/MgO(100) thin films. The electric-field-assisted growth is found to reduce the AF interactions across APBs and, as a consequence, APB-free thin-film-like properties are obtained, which have been probed by electronic, magnetic, and structural characterization. The electric field plays a critical role in controlling the density of APBs during the nucleation process by providing an electrostatic force acting on adatoms and therefore changing their kinetics. This innovative technique can be employed to grow epitaxial spinel thin films with controlled AF interactions across APBs.

Place, publisher, year, edition, pages
American Physical Society, 2018
Keywords
Fe3O4, Epitaxy, Half-metals, Anti-Phase Boundary, Verwey Transition
National Category
Condensed Matter Physics Engineering and Technology
Research subject
Engineering Science with specialization in Solid State Physics
Identifiers
urn:nbn:se:uu:diva-351161 (URN)10.1103/PhysRevMaterials.2.054407 (DOI)000433037500003 ()
Funder
Knut and Alice Wallenberg Foundation, KAW 2012.0031
Available from: 2018-05-21 Created: 2018-05-21 Last updated: 2018-08-15Bibliographically approved
Akansel, S., Venugopal, V., Kumar, A., Gupta, R., Brucas, R., George, S., . . . Svedlindh, P. (2018). Effect of seed layers on dynamic and static magnetic properties of Fe65Co35 thin films. Journal of Physics D: Applied Physics, 51(30), Article ID 305001.
Open this publication in new window or tab >>Effect of seed layers on dynamic and static magnetic properties of Fe65Co35 thin films
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2018 (English)In: Journal of Physics D: Applied Physics, ISSN 0022-3727, E-ISSN 1361-6463, Vol. 51, no 30, article id 305001Article in journal (Refereed) Published
Abstract [en]

Fe65Co35 thin films have been deposited on SiO2 substrates using sputtering technique with different choices of seed layer; Ru, Ni82.5Fe17.5, Rh, Y and Zr. Best soft magnetic properties were observed with seed layers of Ru, Ni82.5Fe17.5 and Rh. Adding these seed layers, the coercivity of the Fe65Co35 films decreased to values of around 1.5 mT, which can be compared to the value of 12.5 mT obtained for films deposited without seed layer. Further investigations were performed on samples with these three seed layers in terms of dynamic magnetic properties, both on as prepared and annealed samples, using constant frequency cavity and broadband ferromagnetic resonance measurements. Damping parameters of around 8.0X10-3 and 4.5X10-3 were obtained from in-plane and out-of-plane measurements, respectively, for as prepared samples, values that were reduced to 6.5X10-3 and 4.0X10-3 for annealed samples.

Keywords
Magnetization dynamics, magnetic thin films, Gilbert damping, ferromagnetic resonance
National Category
Condensed Matter Physics Engineering and Technology
Research subject
Physics with spec. in Atomic, Molecular and Condensed Matter Physics
Identifiers
urn:nbn:se:uu:diva-345853 (URN)10.1088/1361-6463/aaccc0 (DOI)000437408700001 ()
Funder
Knut and Alice Wallenberg Foundation, 2012.0031
Available from: 2018-03-12 Created: 2018-03-12 Last updated: 2018-10-12Bibliographically approved
Tian, B., Liao, X., Svedlindh, P., Strömberg, M. & Wetterskog, E. (2018). Ferromagnetic Resonance Biosensor for Homogeneous and Volumetric Detection of DNA. ACS Sensors, 3(6), 1093-1101
Open this publication in new window or tab >>Ferromagnetic Resonance Biosensor for Homogeneous and Volumetric Detection of DNA
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2018 (English)In: ACS Sensors, ISSN 2379-3694, Vol. 3, no 6, p. 1093-1101Article in journal (Refereed) Published
Abstract [en]

The ability to detect and analyze the state ofmagnetic labels with high sensitivity is of crucial importance fordeveloping magnetic biosensors. In this work, we demonstrate, forthefirst time, a ferromagnetic resonance (FMR) basedhomogeneous and volumetric biosensor for magnetic labeldetection. Two different isothermal amplification methods, i.e.,rolling circle amplification (RCA) and loop-mediated isothermalamplification (LAMP), are adopted and combined with a standardelectron paramagnetic resonance (EPR) spectrometer for FMRbiosensing. For the RCA-based FMR biosensor, binding of RCAproducts of a syntheticVibrio choleraetarget DNA sequence givesrise to the formation of aggregates of magnetic nanoparticles.Immobilization of nanoparticles within the aggregates leads to adecrease of the net anisotropy of the system and a concomitant increase of the resonancefield. A limit of detection of 1 pM isobtained with a linear detection range between 7.8 and 250 pM. For the LAMP-based sensing, a synthetic Zika virus targetoligonucleotide is amplified and detected in 20% serum samples. Immobilization of magnetic nanoparticles is induced by theircoprecipitation with Mg2P2O7(a byproduct of LAMP) and provides a detection sensitivity of 100 aM. The fast measurement,high sensitivity, and miniaturization potential of the proposed FMR biosensing technology makes it a promising candidate fordesigning future point-of-care devices.

National Category
Condensed Matter Physics Engineering and Technology
Research subject
Engineering Science with specialization in Solid State Physics
Identifiers
urn:nbn:se:uu:diva-345595 (URN)10.1021/acssensors.8b00048 (DOI)000436525800005 ()
Funder
Swedish Research Council Formas, 221-2012-444Swedish Research Council Formas, 2011-1692EU, FP7, Seventh Framework Programme, FP7-NMP-601118
Available from: 2018-03-09 Created: 2018-03-09 Last updated: 2018-10-12Bibliographically approved
Organisations
Identifiers
ORCID iD: ORCID iD iconorcid.org/0000-0002-3049-6831

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