| 1. |
- Bručas, Rimantas, et al.
(författare)
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Magnetic and transport properties of Ni81Fe19/Al2O3 granular multilayers approaching the superparamagnetic limit
- 2007
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Ingår i: Journal of Applied Physics. - : AIP Publishing. - 0021-8979 .- 1089-7550. ; 101:7, s. 073907-
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Tidskriftsartikel (refereegranskat)abstract
- The magnetic and transport properties of Ni81Fe 19/Al2O3 granular multilayer films were studied in relation to their structural properties as the nominal thickness t of the permalloy (Ni81Fe19) layer was varied near the percolation limit: in the range of 8≤t≤ 16 Å while keeping the nominal thickness of the Al2O3 layers constant at 16 Å. A good structural quality of the multilayers was demonstrated by low angle x-ray reflectivity measurements, and transmission electron microscopy showed the transition from continuous permalloy layers separated by aluminium oxide layers for t= 16 Å to metal grains dispersed in the insulator at t=8 Å. Magnetization measurements showed the gradual transition from ferromagnetic layers to superparamagnetic clusters and grains that successively become blocked as the temperature decreases. A strong correlation between transport and structural properties was observed in the temperature (T) dependence of the electrical resistance measured with the current in the plane in the range of 2 ≤T≤300 K: a gradual change of behavior from continuous permalloy layers with conducting interlayer connections for t=16 Å. to isolated permalloy grains in a dielectric for the film with t= 10 Å. The percolation occurs between 12 and 10 Å, as deduced both from the magnetic and resistive properties. The discontinuous metal films were analyzed within models for thermally assisted tunneling, yielding estimates of the tunneling barrier for intralayer conduction of about 20 meV for t= 10 Å. A significant magnetic field dependence of the resistance increasing with decreasing temperature was observed in all samples.
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| 2. |
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| 3. |
- Brucas, R., et al.
(författare)
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Magnetic anisotropy and evolution of ground-state domain structures in bcc Fe81Ni19/Co(001) superlattices
- 2008
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Ingår i: Physical Review B. Condensed Matter and Materials Physics. - : The American Physical Society. - 1098-0121 .- 1550-235X. ; 78:2, s. 024421-
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Tidskriftsartikel (refereegranskat)abstract
- The magnetic anisotropy and evolution of striped magnetic domain structures in bcc Fe81Ni19/Co(001) superlattices with the total thickness ranging from 85 to 1370 nm has been studied by magneto-optical Kerr effect and magnetic force microscopy. At a thickness of about 85 nm [25 bilayers (BL)] the domains appear as stripe domains, typical for perpendicular anisotropy films, with the weak cubic anisotropy of the in-plane magnetization component stabilizing the stripe direction. The magnetic domain period strongly depends on the thickness of the superlattice. As the thickness increases, the equilibrium magnetization orients at oblique angles with respect to the film plane and continuously varies with the thickness from in-plane to out-of-plane. We first apply a simple phenomenological model which correctly predicts the transition from in-plane to out-of-plane magnetization as well as increasing domain period and saturation field with increasing BL number. The results indicate the presence of partial flux-closure domains at the film surface with the tilt angle continuously varying with the superlattice thickness. By solving a linearized Landau–Lifshitz equation together with Maxwell’s equations in magnetostatic approximation for samples consisting of up to 1000 individual layers, we calculate the spin-wave dispersion and determine the stability conditions for the saturated ferromagnetic state. From these results the dependence of the saturation field on the number of layers is inferred and agrees well with the experiment. The uniaxial bulk anisotropy is attributed to distortions along the c axis and the results further show evidence for the presence of an easy-plane interface anisotropy in these samples.
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| 4. |
- Brucas, R., et al.
(författare)
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Magnetization and domain structure of bcc Fe81Ni19/Co (001) superlattices
- 2004
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Ingår i: Physical Review B. Condensed Matter and Materials Physics. - 1098-0121 .- 1550-235X. ; 69:6, s. 064411/1-064411/11
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Tidskriftsartikel (refereegranskat)abstract
- Dense stripe domains were obsd. for a Fe81Ni19/Co superlattice grown on a MgO(100) single crystal substrate using dc magnetron sputtering. The stripe domain period exhibits irreversible changes with the magnetic field, as detd. by magnetic force microscopy. We present a simple theor. model for this system and calc. the magnetization and domain period as functions of the applied field by minimizing the total energy. For this purpose, an expression for the domain wall energy and wall width for arbitrary angles and one for the magnetostatic energy are derived. The model correctly predicts a decreasing domain period with the increasing applied field. At larger magnetic fields a transition to "chaotic" two-dimensional stripe patterns is obsd. and a qual. discussion of this phenomenon is given.
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| 5. |
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| 6. |
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| 7. |
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| 8. |
- Haferman, H., et al.
(författare)
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Competing anisotropies in bcc Fe81Ni19/Co(001) superlattices
- 2009
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Ingår i: Applied Physics Letters. - : AIP Publishing. - 0003-6951 .- 1077-3118. ; 94:7, s. 073102-073102-3
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Tidskriftsartikel (refereegranskat)abstract
- Amagnetization reorientation transition has been observed in Fe81Ni19/Co(001) superlattices bymeans of magneto-optical Kerr effect and magnetic force microscopy measurements.The transition is driven by the variation of the interfacedensity. First-principles calculations are combined with a linear stability analysisof the Landau–Lifshitz equation to clarify the mechanism that drivesthe transition. We are able to identify it as beingdriven by competing interface in-plane and uniaxial bulk out-of-plane anisotropies.The origin of the bulk anisotropy is attributed to tetragonaldistortions experimentally observed in these superlattices.
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| 9. |
- Soroka, Inna, et al.
(författare)
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Element-specific magnetic moments in bcc Fe81Ni19/Co superlattices
- 2005
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Ingår i: Physical Review B. Condensed Matter and Materials Physics. - 1098-0121 .- 1550-235X. ; 72:13, s. 134409-
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Tidskriftsartikel (refereegranskat)abstract
- The magnetic moments in bcc Fe81Ni19/Co(001) superlattices with the individual layer thickness of 2-6 monolayers were studied by means of soft x-ray magnetic circular dichroism. It was found that the magnetic moment was enhanced in the Fe81Ni19 layer by about 0.35 mu(B)/atom as compared to the bulk value, while the Co moment remained unaffected by the presence of interfaces. The extension of the region with the high Fe81Ni19 moment in our samples was found to be at least 3 monolayers from the interfaces. Possible sources of the Fe81Ni19 moment enhancement were considered in ab initio calculations, and it was concluded that the enhanced moment may be explained by intermixing and formation of a B2-type short-range order at the interfaces.
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