| 1. |
- Brucas, Rimantas, 1965, et al.
(författare)
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Magnetic and transport properties of discontinuous Ni81 Fe19/Al2O3 multilayers
- 2007
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Ingår i: Journal of Magnetism and Magnetic Materials. - : Elsevier BV. - 0304-8853. ; 310:2 SUPPL. PART 3, s. 2521-2523
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Tidskriftsartikel (refereegranskat)abstract
- The structural percolation and its correlation with the magnetic and transport properties of Ni 81 Fe 19 / Al 2 O 3 multilayer films were studied by varying the thickness (t) of the Ni 81 Fe 19 (permalloy, Py) layers in the range of 10-16 Å, while keeping the Al 2 O 3 layer thickness constant at 16 Å. Low-angle X-ray reflectivity and transmission electron microscopy measurements revealed a good structural quality of the multilayers and showed the transition from continuous Py layers (t = 16 over(A, ̊)) separated by Al 2 O 3 layers to grains (t = 10 over(A, ̊)) dispersed in the insulating matrix. Magnetization measurements showed the gradual transition from ferromagnetic layers (t = 16 over(A, ̊)) to superparamagnetic clusters (t = 12 over(A, ̊)) and isolated grains (t = 10 over(A, ̊)) that successively become blocked as the temperature decreases. The temperature dependence of the current in-plane (CIP) resistance of the samples reveals a change from typical metallic (d R / d T > 0) to dielectric (d R / d T
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| 2. |
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| 3. |
- Brucas, Rimantas, 1965, et al.
(författare)
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Tunneling and charging effects in discontinuous superparamagnetic Ni81Fe19/Al2O3 multilayers
- 2010
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Ingår i: Physical Review B - Condensed Matter and Materials Physics. - : American Physical Society. - 2469-9950 .- 2469-9969 .- 1098-0121 .- 1550-235X. ; 81:22, s. 224437-
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Tidskriftsartikel (refereegranskat)abstract
- The magnetic and transport properties of films based on discontinuous layers of Ni81Fe19 (Py) embedded in Al2O3 were investigated. In films with nominal Py thicknesses 6 and 8 angstrom superparamagnetic particles with median diameters D-med = 2.8 and 3.1 nm and distribution widths sigma(D)= 1.2 and 1.3 nm were formed. Current voltage (IU) curves were measured with the current perpendicular to the film plane. The analyses show that the charge transport occurs via tunneling; with the charging energy supplied by thermal fluctuations at high temperature, T >= 100 K, and by the electric field at low temperature, T
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| 4. |
- Felton, S., et al.
(författare)
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Micromagnetic studies of Fe/Co ellipses with competing anisotropy contributions
- 2004
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Ingår i: Journal of Magnetism and Magnetic Materials. - : Elsevier BV. - 0304-8853. ; 272-276:SUPPL. 1, s. e1297-
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Tidskriftsartikel (refereegranskat)abstract
- The effects of competing magneto-crystalline and shape anisotropies on magnetization reversal were studied in situ in arrays of sub-micron Fe/Co ellipses of compositions Fe2/Co6 and Fe8/Co3 with magnetic force microscopy (MFM). A simple model assigning magnetization values to the different types of domain structures observed in the MFM images was used to estimate the field dependence of the total magnetization of a sample. The agreement with macroscopic magnetization measurements is discussed.
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| 5. |
- Flovik, Vegard, et al.
(författare)
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Tailoring the magnetodynamic properties of nanomagnets using magnetocrystalline and shape anisotropies
- 2015
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Ingår i: Physical Review B. Condensed Matter and Materials Physics. - 1098-0121 .- 1550-235X .- 2469-9950 .- 2469-9969. ; 92:10
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Tidskriftsartikel (refereegranskat)abstract
- Magnetodynamical properties of nanomagnets are affected by the demagnetizing fields created by the same nanoelements. In addition, magnetocrystalline anisotropy produces an effective field that also contributes to the spin dynamics. We show how the dimensions of magnetic elements can be used to balance crystalline and shape anisotropies, and that this can be used to tailor the magnetodynamic properties. We study ferromagnetic ellipses patterned from a 10-nm-thick epitaxial Fe film with dimensions ranging from 50x150 to 150x450 nm. The study combines ferromagnetic resonance (FMR) spectroscopy with analytical calculations and micromagnetic simulations, and proves that the dynamical properties can be effectively controlled by changing the size of the nanomagnets. We also show how edge defects in the samples influence the magnetization dynamics. Dynamical edge modes localized along the sample edges are strongly influenced by edge defects, and this needs to be taken into account in understanding the full FMR spectrum.
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| 6. |
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| 7. |
- Gunnarsson, Robert, 1972, et al.
(författare)
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Magnetization reversal processes in magnetic bicrystal junctions
- 2006
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Ingår i: Phys. Rev. B. ; 73, s. 014435-
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Tidskriftsartikel (refereegranskat)abstract
- We provide experimental data for the magnetoresistance in epitaxial ferromagnetic manganite (La0.7Sr0.3MnO3) bicrystals with various angles. Experiments were conducted using samples with in-plane magnetization as well as with out-of-plane magnetization. The magnetoresistance hysteresis is interpreted directly into different magnetization reversal processes. We show that it is possible to set the electrode magnetization at remanence such that the spins at the bicrystal interface are either parallel or inclined to each other at an angle determined by the crystal orientations. Finally, we demonstrate the feasibility of using epitaxial magnetic bicrystals to probe the transport properties in magnetic junctions with well-determined angles of magnetization.
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| 8. |
- Gunnarsson, Robert, 1972, et al.
(författare)
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Magnetoresistance in bicrystal grain-boundary junctions analyzed within the Stoner-Wohlfarth model
- 2005
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Ingår i: Journal of Magnetism and Magnetic Materials. - : Elsevier BV. - 0304-8853 .- 1873-4766. ; 290-291:part 1, s. 761-763
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Tidskriftsartikel (refereegranskat)abstract
- Experimental data of bicrystal grain boundary magnetoresistance hysteresis shows that the resistance at remanence after saturation depends on whether the magnetic field was applied parallel or perpendicular to the grain boundary. In the latter case the behaviour can be described by the Stoner-Wohlfarth magnetization reversal model for coherent rotation of the magnetization, which leads to an alignment along the easy magnetization directions of the bicrystal in zero field. In the parallel configuration themagnetization directions of the two grains remain parallel in zero field. We have used this information to deduce an effective spin-polarization of P ~ 40 % of the grain boundary in a bicrystal of La0.7Sr0.3MnO3.
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| 9. |
- Gunnarsson, Robert, 1972, et al.
(författare)
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Misorientation angle dependence of bicrystal magnetoresistance within the model of coherent rotation
- 2004
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Ingår i: Journal of Physics: Condensed Matter. - : IOP Publishing. ; 16:21, s. 3761-3768
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Tidskriftsartikel (refereegranskat)abstract
- The bicrystal magnetoresistance hysteresis is studied within the model of coherent rotation of magnetization. The magnetoresistance hysteresis is calculated numerically in the limit of fully spin polarized current for symmetric bicrystal junctions with biaxial magnetic anisotropy and of varying misorientation angles. The shape of the curves obtained from the model displays different characteristic features, depending on the angular relationships, which are consistent with experimental data from the literature. The results show a magnetoresistance increasing with increasingmisorientation angle. The influence of biaxial magnetocrystalline anisotropy is reflected in a hump in the maximum magnetoresistance curve at around a misorientation angle of 25 degrees. This structure is absent in the case of uniaxial anisotropy.
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| 10. |
- Gunnarsson, Robert, 1972, et al.
(författare)
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Stoner-Wohlfarth model applied to bicrystal magnetoresistance hysteresis
- 2004
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Ingår i: Journal of Applied Physics. - : AIP Publishing. - 0021-8979 .- 1089-7550. ; 96:1, s. 482-485
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Tidskriftsartikel (refereegranskat)abstract
- We calculate numerically the magnetization direction as function of magnetic field in the StonerWohlfarth theory and are able to reproduce the shape of the low-field magnetoresistance hysteresis observed in manganite grain boundary junctions. Moreover, we show that it is necessary to include biaxial magnetocrystalline anisotropy to fully describe the grain boundary magnetoresistance in La0.7Sr0.3MnO3/SrTiO3 bicrystal tunnel junctions.
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