| 1. |
- Demidov, V. V., et al.
(författare)
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Magnetic anisotropy in strained manganite films and bicrystal junctions
- 2013
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Ingår i: Journal of Applied Physics. - : AIP Publishing. - 0021-8979 .- 1089-7550. ; 113:16
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Tidskriftsartikel (refereegranskat)abstract
- Transport and magnetic properties of La0.67Sr0.33MnO3 (LSMO) manganite thin films and bicrystal junctions were investigated. Epitaxial manganite films were grown on SrTiO3, LaAlO3, NdGaO3 (NGO), and (LaAlO3)(0.3) + (Sr2AlTaO6)(0.7) substrates, and their magnetic anisotropy were determined by two independent techniques of magnetic resonance spectroscopy. It was demonstrated that by using these techniques, a small (0.3%) anisotropy of crystal structure at the (110) surface plane of the orthorhombic NGO substrate leads to uniaxial magnetic anisotropy of the films in the plane of the substrate at least at the room temperature. It was found that on vicinal NGO substrates, the value of magnetic anisotropy strength can be varied in the range 100-200 Oe at T = 295 K by changing the substrate vicinal angle from 0 degrees to 25 degrees. Measurement of the magnetic anisotropy of manganite bicrystal junction demonstrated the presence of two ferromagnetic spin subsystems for both types of bicrystal boundaries with tilting of basal plane of manganite tilted bicrystal (TB-junction) and with rotation of crystallographic axes (RB-junction) used for comparison. The magnetoresistance of TB-junctions increases with decreasing temperature and the misorientation angle. Variation of bicrystal misorientation angle does not lead to change of misorientation of easy magnetic axes in the film parts forming TB-junction. Analysis of the voltage dependencies of bicrystal junction conductivity show that the low value of the magnetoresistance for the LSMO bicrystal junctions can be caused by two scattering mechanisms. The first one is the spin-flip of spin-polarized carriers due to the strong electron-electron interactions in a disordered layer at the bicrystal boundary at low temperatures and the second one is spin-flip by antiferromagnetic magnons at high temperatures.
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| 2. |
- 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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| 3. |
- Gunnarsson, Robert, 1972
(författare)
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Anisotropic spin-orbit interaction revealed by in-plane magnetoresistance in single-oriented SrRuO3 thin films
- 2012
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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. ; 85:23, s. 235409-
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Tidskriftsartikel (refereegranskat)abstract
- A detailed analysis of the in-plane magnetoresistance anisotropy in single orientation thin filmSrRuO3 grown on (001)SrTiO3 is presented. The resistivity is measured in strips along [001], [¯110]and [¯11¯1] with in-plane rotating magnetic field. The data show new details in the transfer fromnegative to positive magnetoresistance when the field is rotated in the plane. They show that themagnetoresistance is anisotropic with respect to the crystalline directions rather than with respectto the direction of the current. The data suggest an
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| 4. |
- 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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| 5. |
- 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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| 6. |
- 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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| 7. |
- Kalaboukhov, Alexei, 1975, et al.
(författare)
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Electrical and structural properties of ABO3/SrTiO3 interfaces
- 2012
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Ingår i: Materials Research Society Symposium Proceedings. - Warrendale, Pa. : Springer Science and Business Media LLC. - 0272-9172. - 9781605114316 ; 1454, s. 167-172, s. 167-172
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Konferensbidrag (refereegranskat)abstract
- Electrical transport and microstructure of interfaces between nm-thick films of various perovskite oxides grown by pulsed laser deposition (PLD) on TiO2 terminated SrTiO3 (STO) substrates are compared. LaAlO3/STO and KTaO3/STO interfaces become quasi-2DEG after a critical film thickness of 4 unit cell layers. The conductivity survives long anneals in oxygen atmosphere. LaMnO3/STO interfaces remain insulating for all film thicknesses and NdGaO3/STO interfaces are conducting but the conductivity is eliminated after oxygen annealing. Medium-energy ion spectroscopy and scanning transmission electron microscopy detect cationic intermixing within several atomic layers from the interface in all studied interfaces. Our results indicate that the electrical reconstruction in the polar oxide interfaces is a complex combination of different mechanisms, and oxygen vacancies play an important role.
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| 8. |
- Stepantsov, Evgeny, et al.
(författare)
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Ablation replacement of iron with Co, Mn, Ni, and Cu during growth of iron-based superconductor films in the Fe0.9M0.1Se0.92 system
- 2014
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Ingår i: Crystallography reports (Print). - 1063-7745 .- 1562-689X. ; 59:5, s. 739-743
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Tidskriftsartikel (refereegranskat)abstract
- Thin films of ironbased chalcogenide superconductors FeSe0.92, with iron partially replaced (atleast up to 10 at %) by elements such as cobalt, nickel, manganese, or copper, have been grown on the surfaceof (10 2) LaAlO3 crystals. Growth is performed by the laser ablation of a target prepared in the form of aceramic pellet by hightemperature synthesis and the sintering of preliminarily pressed stoichiometric mixture of powders. Iron in these ceramics is replaced with an alloying metal by no more than 3 at %. The rest(7 at %) of the metal is in the form of precipitates of other phases. Xray diffraction analysis of the grown filmshas shown that they are singlecrystal and free of any precipitates of other crystallographic orientations andphases. This is evidence of the complete (10 at %) replacement of iron with a doping metal in the film structure. This circumstance indicates that the synthesis of components occurs more actively and completely during laser ablation (than in solidphase chemical reactions) as a result of the transformation of multicomponent target material into plasma. Thus, one can fabricate film materials in a wider range of chemical compositions than in the form of solidphase synthesized ceramics.
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