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Gupta, R., Behera, N., Venugopal, V. A., Basu, S., Puri, A. K., Ström, P., . . . Kumar, A. (2020). Engineering of spin mixing conductance at Ru/FeCo/Ru interfaces: Effect of Re doping. Physical Review B. Condensed Matter and Materials Physics, 101(2), Article ID 024401.
Open this publication in new window or tab >>Engineering of spin mixing conductance at Ru/FeCo/Ru interfaces: Effect of Re doping
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2020 (English)In: Physical Review B. Condensed Matter and Materials Physics, ISSN 1098-0121, E-ISSN 1550-235X, Vol. 101, no 2, article id 024401Article in journal (Refereed) Published
Abstract [en]

We have deposited polycrystalline Re-doped (Fe65Co35)(100-x)Rex (0 ≤ x ≤ 12.6 at. %) thin films grown under identical conditions and sandwiched between thin layers of Ru in order to study the phenomenon of spin pumping as a function of Re concentration. In-plane and out-of-plane ferromagnetic resonance spectroscopy results show an enhancement of the Gilbert damping with an increase in Re doping. We find 98% enhancement in the real part of effective spin mixing conductance [Re(g↑↓eff)] with Re doping. Conversely, the Re(g↑↓eff) does not change with Re doping in Fe65Co35 thin films which are seeded and capped with Cu layers. The enhancement in Re(g↑↓eff) of Re-doped Fe65Co35 thin films sandwiched between thin layers of Ru is linked to the Re doping-induced change of the interface electronic structure in the nonmagnetic Ru layer. The saturation magnetization decreases 35% with increasing Re doping up to 12.6 at. %. This study opens a direction of tuning the spin mixing conductance in magnetic heterostructures by doping of the ferromagnetic layer, which is essential for the realization of energyefficient operation of spintronic devices.

Keywords
spin dynamics, ferromagnetic resonance, spin pumping
National Category
Condensed Matter Physics
Research subject
Engineering Science with specialization in Solid State Physics; Engineering Science with specialization in Materials Science; Physics with spec. in Atomic, Molecular and Condensed Matter Physics
Identifiers
urn:nbn:se:uu:diva-402756 (URN)10.1103/PhysRevB.101.024401 (DOI)000505982500003 ()
Funder
Swedish Research Council, 2017-03799Stiftelsen Olle Engkvist Byggmästare, 182-0365EU, FP7, Seventh Framework Programme, 612170Swedish Research Council, 2017-00646_9Swedish Foundation for Strategic Research , RIF14-0053
Available from: 2020-02-01 Created: 2020-02-01 Last updated: 2020-03-31Bibliographically approved
Karpiak, B., Cummings, A. W., Zollner, K., Vila, M., Khokhriakov, D., Hoque, A. M., . . . Dash, S. P. (2020). Magnetic proximity in a van der Waals heterostructure of magnetic insulator and graphene. 2D MATERIALS, 7, Article ID 015026.
Open this publication in new window or tab >>Magnetic proximity in a van der Waals heterostructure of magnetic insulator and graphene
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2020 (English)In: 2D MATERIALS, ISSN 2053-1583, Vol. 7, article id 015026Article in journal (Refereed) Published
Abstract [en]

Engineering 2D material heterostructures by combining the best of different materials in one ultimate unit can offer a plethora of opportunities in condensed matter physics. Here, in the van der Waals heterostructures of the ferromagnetic insulator Cr2Ge2Te6 and graphene, our observations indicate an out-of-plane proximity-induced ferromagnetic exchange interaction in graphene. The perpendicular magnetic anisotropy of Cr2Ge2Te6 results in significant modification of the spin transport and precession in graphene, which can be ascribed to the proximity-induced exchange interaction. Furthermore, the observation of a larger lifetime for perpendicular spins in comparison to the in-plane counterpart suggests the creation of a proximity-induced anisotropic spin texture in graphene. Our experimental results and density functional theory calculations open up opportunities for the realization of proximity-induced magnetic interactions and spin filters in 2D material heterostructures and can form the basic building blocks for future spintronic and topological quantum devices.

Place, publisher, year, edition, pages
IOP PUBLISHING LTD, 2020
Keywords
graphene, 2D ferromagnet, van der Waals heterostructures, Cr2Ge2Te6, proximity effect, magnetism, spin anisotropy
National Category
Condensed Matter Physics
Identifiers
urn:nbn:se:uu:diva-402654 (URN)10.1088/2053-1583/ab5915 (DOI)000504310700001 ()
Funder
EU, Horizon 2020, 785219Swedish Research Council, 2015-06813Swedish Research Council, 2016-03658
Available from: 2020-01-20 Created: 2020-01-20 Last updated: 2020-01-20Bibliographically approved
Pogoryelov, Y., Pereiro, M., Jana, S., Kumar, A., Akansel, S., Ranjbar, M., . . . Arena, D. A. (2020). Nonreciprocal spin pumping damping in asymmetric magnetic trilayers. Physical Review B, 101(5), Article ID 054401.
Open this publication in new window or tab >>Nonreciprocal spin pumping damping in asymmetric magnetic trilayers
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2020 (English)In: Physical Review B, ISSN 2469-9950, E-ISSN 2469-9969, Vol. 101, no 5, article id 054401Article in journal (Refereed) Published
Abstract [en]

In magnetic trilayer systems, spin pumping is generally addressed as a reciprocal mechanism characterized by one unique spin-mixing conductance common to both interfaces. However, this assumption is questionable in cases where different types of interfaces are present. Here, we present a general theory for analyzing spin pumping in cases with more than one unique interface and where the magnetic coupling is allowed to be noncollinear. The theory is applied to analyze layer-resolved ferromagnetic resonance experiments on the trilayer system Ni80Fe20/Ru/Fe49Co49V2 where the Ru spacer thickness is varied to tune the indirect exchange coupling. It is demonstrated that the equation of motion of macrospins driven by spin pumping need to be modified in case of noncollinear coupling. Our analysis also shows that the spin pumping in trilayer systems with dissimilar magnetic layers, in general, is nonreciprocal.

Place, publisher, year, edition, pages
AMER PHYSICAL SOC, 2020
National Category
Condensed Matter Physics
Identifiers
urn:nbn:se:uu:diva-406460 (URN)10.1103/PhysRevB.101.054401 (DOI)000510745200002 ()
Funder
Knut and Alice Wallenberg FoundationSwedish Foundation for Strategic Research Swedish Energy AgencySwedish Research Council, 2016-04524Swedish Research Council, 2013-08316
Available from: 2020-03-09 Created: 2020-03-09 Last updated: 2020-03-09Bibliographically approved
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
Ciuciulkaite, A., Östman, E., Brucas, R., Kumar, A., Verschuuren, M. A., Svedlindh, P., . . . Kapaklis, V. (2019). Collective magnetization dynamics in nanoarrays of thin FePd disks. Physical Review B, 99(18), Article ID 184415.
Open this publication in new window or tab >>Collective magnetization dynamics in nanoarrays of thin FePd disks
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2019 (English)In: Physical Review B, ISSN 2469-9950, E-ISSN 2469-9969, Vol. 99, no 18, article id 184415Article in journal (Refereed) Published
Abstract [en]

We report on the magnetization dynamics of a square array of mesoscopic disks, fabricated from an iron palladium alloy film. The dynamics properties were explored using ferromagnetic resonance measurements and micromagnetic simulations. The obtained spectra exhibit features resulting from the interactions between the disks, with a clear dependence on both temperature and the direction of the externally applied field. We demonstrate a qualitative agreement between the measured and calculated spectra. Furthermore, we calculated the mode profiles of the standing spin waves excited during time-dependent magnetic field excitations. The resulting maps confirm that the features appearing in the ferromagnetic resonance absorption spectra originate from the temperature- and directional-dependent interdisk interactions.

Place, publisher, year, edition, pages
AMER PHYSICAL SOC, 2019
National Category
Condensed Matter Physics
Identifiers
urn:nbn:se:uu:diva-386163 (URN)10.1103/PhysRevB.99.184415 (DOI)000468206200003 ()
Funder
Swedish Research CouncilKnut and Alice Wallenberg Foundation, 2015.0060The Swedish Foundation for International Cooperation in Research and Higher Education (STINT)EU, Horizon 2020, 737093
Available from: 2019-06-20 Created: 2019-06-20 Last updated: 2019-06-20Bibliographically approved
Akansel, S., Kumar, A., Venugopal, V. A., Esteban-Puyuelo, R., Banerjee, R., Autieri, C., . . . Svedlindh, P. (2019). Enhanced Gilbert damping in Re-doped FeCo films: Combined experimental and theoretical study. Physical Review B, 99(17), Article ID 174408.
Open this publication in new window or tab >>Enhanced Gilbert damping in Re-doped FeCo films: Combined experimental and theoretical study
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2019 (English)In: Physical Review B, ISSN 2469-9950, E-ISSN 2469-9969, Vol. 99, no 17, article id 174408Article in journal (Refereed) Published
Abstract [en]

The effects of rhenium doping in the range 0-10 at.% on the static and dynamic magnetic properties of Fe65Co35 thin films have been studied experimentally as well as with first-principles electronic structure calculations focusing on the change of the saturation magnetization (M-s) and the Gilbert damping parameter (alpha). Both experimental and theoretical results show that M-s decreases with increasing Re-doping level, while at the same time alpha increases. The experimental low temperature saturation magnetic induction exhibits a 29% decrease, from 2.31 to 1.64 T, in the investigated doping concentration range, which is more than predicted by the theoretical calculations. The room temperature value of the damping parameter obtained from ferromagnetic resonance measurements, correcting for extrinsic contributions to the damping, is for the undoped sample 2.1 x 10(-3), which is close to the theoretically calculated Gilbert damping parameter. With 10 at.% Re doping, the damping parameter increases to 7.8 x 10(-3), which is in good agreement with the theoretical value of 7.3 x 10(-3). The increase in damping parameter with Re doping is explained by the increase in the density of states at the Fermi level, mostly contributed by the spin-up channel of Re. Moreover, both experimental and theoretical values for the damping parameter weakly decrease with decreasing temperature.

National Category
Condensed Matter Physics
Identifiers
urn:nbn:se:uu:diva-387290 (URN)10.1103/PhysRevB.99.174408 (DOI)000467722100005 ()
Funder
Knut and Alice Wallenberg Foundation, KAW 2012.0031Swedish Research Council, 2016-05366
Available from: 2019-06-24 Created: 2019-06-24 Last updated: 2019-06-24Bibliographically 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
Etman, A. S., Pell, A. J., Svedlindh, P., Hedin, N., Zou, X., Sun, J. & Bernin, D. (2019). Insights into the Exfoliation Process of V2O5 center dot nH(2)O Nanosheet Formation Using Real-Time V-51 NMR. ACS OMEGA, 4(6), 10899-10905
Open this publication in new window or tab >>Insights into the Exfoliation Process of V2O5 center dot nH(2)O Nanosheet Formation Using Real-Time V-51 NMR
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2019 (English)In: ACS OMEGA, ISSN 2470-1343, Vol. 4, no 6, p. 10899-10905Article in journal (Refereed) Published
Abstract [en]

Nanostructured hydrated vanadium oxides (V2O5 center dot nH(2)O) are actively being researched for applications in energy storage, catalysis, and gas sensors. Recently, a one-step exfoliation technique for fabricating V2O5 center dot nH(2)O nano-sheets in aqueous media was reported; however, the underlying mechanism of exfoliation has been challenging to study. Herein, we followed the synthesis of V2O5 center dot nH(2)O nanosheets from the V2O5 and VO2 precursors in real using solution- and solid-state V-51 NMR. Solution-state V-51 NMR showed that the aqueous solution contained mostly the decavanadate anion [H2V10O28](4-) and the hydrated dioxova-nadate cation [VO2 center dot 4H(2)O](+), and during the exfoliation process, decavanadate was formed, while the amount of [VO2 center dot 4H(2)O](+) remained constant. The conversion of the solid precursor V2O5, which was monitored with solid-state V-51 NMR, was initiated when VO2 was in its monoclinic forms. The dried V2O5 center dot nH(2)O nanosheets were weakly paramagnetic because of a minor content of isolated V4+. Its solid-state V-51 signal was less than 20% of V2O5 and arose from diamagnetic V4+ or V5+.This study demonstrates the use of real-time NMR techniques as a powerful analysis tool for the exfoliation of bulk materials into nanosheets. A deeper understanding of this process will pave the way to tailor these important materials.

Place, publisher, year, edition, pages
AMER CHEMICAL SOC, 2019
National Category
Materials Chemistry
Identifiers
urn:nbn:se:uu:diva-390643 (URN)10.1021/acsomega.9b00727 (DOI)000473361500150 ()
Available from: 2019-08-19 Created: 2019-08-19 Last updated: 2019-08-19Bibliographically 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., Barwal, V., Kumar, A., Gupta, R., Behera, N., Hait, S., . . . Chaudhary, S. (2019). Multi-jump magnetization switching in Co2FeAl full Heusler alloy thin films: Experiments and simulations. Journal of Magnetism and Magnetic Materials, 486, Article ID 165258.
Open this publication in new window or tab >>Multi-jump magnetization switching in Co2FeAl full Heusler alloy thin films: Experiments and simulations
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2019 (English)In: Journal of Magnetism and Magnetic Materials, ISSN 0304-8853, E-ISSN 1873-4766, Vol. 486, article id 165258Article in journal (Refereed) Published
Abstract [en]

Co2FeAl (CFA) thin films of 50 nm thickness have been grown on MgO (001) single crystal substrates at room temperature with and without post-annealing (PA) at 300 degrees C and 400 degrees C using dual ion-beam sputtering technique. The XRD pattern of the as-grown film revealed that CFA grows with preferred crystallographic orientation on the MgO (001) substrate. Temperature dependent anisotropy measurements on PA films revealed a dominating contribution from cubic anisotropy as confirmed by the analysis of azimuthal angle dependent longitudinal in-plane magneto-optical Kerr effect (MOKE) measurements. The contributions from the cubic and uniaxial anisotropies have also been quantified employing ferromagnetic resonance spectroscopy. Magnetization reversal is accompanied with a plateau in the MOKE hysteresis recorded at various azimuthal angles in the in-plane applied magnetic field configuration. The occurrence of the observed plateau is explained by the presence of a combination of domain walls such as 90 degrees, 135 degrees and 180 degrees domain walls and/or complex domains which is supported by results from micromagnetic simulations. These results demonstrate the feasibility of manipulating the magnetization switching in one of the two ferromagnetic electrodes of the magnetic tunnel junction devices based on Heusler alloy ferromagnetic films.

Place, publisher, year, edition, pages
ELSEVIER SCIENCE BV, 2019
Keywords
Hensler alloy, Magneto-optical Kerr effect, Cubic anisotropy, Micromagnetic simulations
National Category
Condensed Matter Physics
Identifiers
urn:nbn:se:uu:diva-390070 (URN)10.1016/j.jmmm.2019.165258 (DOI)000471859200024 ()
Funder
Knut and Alice Wallenberg Foundation, KAW 2012.0031
Available from: 2019-08-07 Created: 2019-08-07 Last updated: 2019-08-07Bibliographically approved
Organisations
Identifiers
ORCID iD: ORCID iD iconorcid.org/0000-0002-3049-6831

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