| 1. |
- Boikov, Iouri, 1949, et al.
(författare)
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Strain-enhanced phase separation affecting electro- and magnetotransport in La0.67Ca0.33MnO3 films
- 2004
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Ingår i: Journal of Applied Physics. ; 96:1, s. 435-442
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Tidskriftsartikel (refereegranskat)abstract
- Biaxial strain during nucleation influences phase separation into ferromagnetic (metallic) and nonferromagnetic (insulating) regions and that, in turn, markedly affects the electric transport of a manganite film. A 40-nm-thick La0.67Ca0.33MnO3 film, coherently constrained by a (001)LaAlO3 substrate, possesses a noticeably contracted unit cell volume (Veff[approximate]56.70 Å3) as compared with that of a stoichiometric bulk sample. It corresponds to a higher relative concentration (45%) of tetravalent manganese ions in the manganite layer than that in the target (33%). The resistivity rho(T) curve of the strained film peaks twice in the range 4.2300 K. The charge transport of strained La0.67Ca0.33MnO3 films is non-ohmic at T
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| 2. |
- Gunnarsson, Robert, 1972, et al.
(författare)
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Fabrication and characterisation of La0.67Sr0.33MnO3 submicron grain boundary junctions
- 2004
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Ingår i: Annalen der Physik (Leipzig). ; 13:1-2, s. 101-102
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Konferensbidrag (refereegranskat)abstract
- We have successfully fabricated LSMO grain boundary bicrystaljunctions with widths down to 200 nm. The grain boundaries aresymmetric with misorientation angles of 24degrees or 36.8degrees, and the microbridges are positioned across thosewith a precision better than 0.5 micro-meter. Grain boundary magnetoresistance is observed in the wider junctions but not in the most narrow junction.
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| 3. |
- Gunnarsson, Robert, 1972, et al.
(författare)
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Low-field magnetoresistance in perovskite manganites: Magnetic field, temperature, and current dependence
- 2004
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Ingår i: Physical Review B. ; 69:5, s. 054413-
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Tidskriftsartikel (refereegranskat)abstract
- The low-field response from single bicrystal grain boundary junction of La0.7Sr0.3MnO3 has been investigated. We provide experimental data for the temperature, magnetic field and bias current dependence of its low-field magnetoresistance. We are then able to separate the contribution from anisotropic magnetoresistance, and the magnetization processes in the vicinity of the grain boundary. Our data indicate that with the magnetic field applied parallel to the grain boundary the magnetization process is dominated by domain wall motion, whereas with the field in the perpendicular direction the magnetoresistance is determinedby coherent rotation of magnetization directions.
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| 4. |
- Gunnarsson, Robert, 1972
(författare)
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Magnetic Bicrystal Junctions - a Study of Half-Metallic Manganite Grain Boundaries
- 2004
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- This thesis presents studies on magnetic bicrystal junctions. In these, films on either side of the junction are structurally and magnetically misoriented. This type of device enables us to study junction magnetoresistance and spin polarized charge transport between ferromagnets with well defined directions of magnetization. The ferromagnets subject to our studies are epitaxial films, prepared by pulsed laser deposition, of La0.7Sr0.3MnO3, suggested to possess half-metallic characteristics. The electrical transport through single and arrays of junctions have been measured as functions of magnetic field and temperature. We have demonstrated that the magnetization reversal processes responsible for the magnetoresistance observed in poly-crystalline films can be studied in detail by using single bicrystal grain boundary junctions. We have shown that when the field is applied perpendicular to a grain boundary, the magnetization reversal process can be well described by a Stoner-Wohlfarth model for coherent rotation of magnetization. Whereas, when the field is applied along the grain boundary, the magnetoresistance data suggest a stochastic reversal process, including splitting into domains. Coherent rotation of magnetization is an essential ingredient when modelling the magnetoresistance hysteresis. We have observed, by high resolution electron microscopy, that the region of structural disorder at the bicrystal interface can be small, with a width as small as down to a unit-cell. Different models have been discussed for the transport mechanism across the interface. Current-voltage characteristics of single junctions are close to Ohmic at low voltage, and become non-linear at voltages higher than 5 - 20 mV, depending on misorientation angle. However, they cannot be fitted to a simple parabolic function. The results are discussed in terms of a tunnelling model.
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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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