Abstract
This study presents a systematic investigation of the SSV effect in FM/SC/FM and FM/N/FM/SC heterostructures. Before investigating the actual SSV effect, we first pre-analyzed structural, magnetic and superconducting properties of the Fe/V system. In these preliminary studies we demonstrated, that epitaxial Fe/V heterostructures of superior crystalline quality can be grown by DC sputter deposition. With a Fe/V interface thickness of only one monolayer, the chemical separation of the Fe and V layers is extremely sharp. Moreover, the magnetic investigation showed that from thicknesses of two Fe(001) monolayers on the Fe layers in the superlattice possess a magnetic moment. Furthermore, we demonstrated the interlayer exchange coupling as oscillatory function of the V interlayer thickness. The investigations of the superconducting parameters of the Fe/V system revealed a non-monotonic T{sub S} vs. d{sub Fe} dependence in sample series (1). This observation proves the presence of the FM/SC proximity effect. The studies of various heterostructures of the design AFM/FM/SC/FM revealed a strong counteracting influence on the SSV effect, the stray field effect. The sample containing Fe{sub 25}V{sub 75} alloy layers, has the highest ratio of Cooper pair coherence length and superconductor thickness (ξ{sub S})/(d{sub S}), and its superconducting transition temperature is comparable to the
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Citation Formats
Nowak, Gregor.
Superconducting spin valves based on epitaxial Fe/V-hybrid thin film heterostructures.
Germany: N. p.,
2010.
Web.
Nowak, Gregor.
Superconducting spin valves based on epitaxial Fe/V-hybrid thin film heterostructures.
Germany.
Nowak, Gregor.
2010.
"Superconducting spin valves based on epitaxial Fe/V-hybrid thin film heterostructures."
Germany.
@misc{etde_22545937,
title = {Superconducting spin valves based on epitaxial Fe/V-hybrid thin film heterostructures}
author = {Nowak, Gregor}
abstractNote = {This study presents a systematic investigation of the SSV effect in FM/SC/FM and FM/N/FM/SC heterostructures. Before investigating the actual SSV effect, we first pre-analyzed structural, magnetic and superconducting properties of the Fe/V system. In these preliminary studies we demonstrated, that epitaxial Fe/V heterostructures of superior crystalline quality can be grown by DC sputter deposition. With a Fe/V interface thickness of only one monolayer, the chemical separation of the Fe and V layers is extremely sharp. Moreover, the magnetic investigation showed that from thicknesses of two Fe(001) monolayers on the Fe layers in the superlattice possess a magnetic moment. Furthermore, we demonstrated the interlayer exchange coupling as oscillatory function of the V interlayer thickness. The investigations of the superconducting parameters of the Fe/V system revealed a non-monotonic T{sub S} vs. d{sub Fe} dependence in sample series (1). This observation proves the presence of the FM/SC proximity effect. The studies of various heterostructures of the design AFM/FM/SC/FM revealed a strong counteracting influence on the SSV effect, the stray field effect. The sample containing Fe{sub 25}V{sub 75} alloy layers, has the highest ratio of Cooper pair coherence length and superconductor thickness (ξ{sub S})/(d{sub S}), and its superconducting transition temperature is comparable to the sample with Fe{sub 35}V{sub 65} alloy layers. Nevertheless, the SSV effect in sample Fe{sub 25}V{sub 75} with alloy layers is much smaller than in sample with Fe{sub 35}V{sub 65} alloy layers. For a high-performance superconducting spin valve based on a FM1/SC/FM2 heterostructure at least four parameters have to be optimized simultaneously. 1. The magnetic domain size in FM1 and FM2 has to be as large as possible in order to reduce the stray field effect resulting from magnetization components in the FM domain walls perpendicular to the SC layer. 2. When using ferromagnetic alloys as screening layers to suppress the stray field effect, the concentration of the ferromagnetic component in the alloy should be high enough to avoid the generation of non-magnetic/paramagnetic layers. Paramagnetic layers induce pair breaking, thus reducing the quantum-mechanical transparency T{sub F} for the Cooper pair wave function at the FM/SC interface. 3. Ferromagnetic alloys should be chosen as to achieve a better band structure match between the ferromagnetic component and the superconductor. Thereby, T{sub F} will be increased, augmenting the SSV effect. 4. The distance between FM1 and FM2, i.e. the thickness of the superconductor d{sub S}, should be of the order of the Cooper pair coherence length ξ{sub S} ∼ d{sub S}. Ideally, (ξ{sub S})/(d{sub S}) ∼ 1 or larger (see 125), since then the Cooper pair wave function is most effectively influenced by both magnetic layers FM1 and FM2. In the AFM/FM/SC/FM heterostructures, which we prepared according to these guidelines, we could observe satisfying switching characteristics, and SSV effects up to ΔT{sub S} = 20 mK. In this study we have verified the magnetic and superconducting properties of the unusual sample containing a [Fe(2ML)/V(180ML)] superlattice by means of conventional SQUID magnetometry as well as polarized neutron scattering (PNR) method. In the PNR we found a magnetic splitting in the PNR curves for the normal and superconducting state of the sample. Further we found weak indications for a reduction of the magnetic splitting beyond the error bars in the superconducting state compared to the normal conducting state of the sample, what can be considered as a weak indication of the Inverse Proximity effect. However, the measured spin asymmetry difference of the magnetic splitting between the superconducting and normal conducting state of the sample is not clear enough to give an unambiguous answer on the presence or absence of the inverse proximity effect.}
place = {Germany}
year = {2010}
month = {Dec}
}
title = {Superconducting spin valves based on epitaxial Fe/V-hybrid thin film heterostructures}
author = {Nowak, Gregor}
abstractNote = {This study presents a systematic investigation of the SSV effect in FM/SC/FM and FM/N/FM/SC heterostructures. Before investigating the actual SSV effect, we first pre-analyzed structural, magnetic and superconducting properties of the Fe/V system. In these preliminary studies we demonstrated, that epitaxial Fe/V heterostructures of superior crystalline quality can be grown by DC sputter deposition. With a Fe/V interface thickness of only one monolayer, the chemical separation of the Fe and V layers is extremely sharp. Moreover, the magnetic investigation showed that from thicknesses of two Fe(001) monolayers on the Fe layers in the superlattice possess a magnetic moment. Furthermore, we demonstrated the interlayer exchange coupling as oscillatory function of the V interlayer thickness. The investigations of the superconducting parameters of the Fe/V system revealed a non-monotonic T{sub S} vs. d{sub Fe} dependence in sample series (1). This observation proves the presence of the FM/SC proximity effect. The studies of various heterostructures of the design AFM/FM/SC/FM revealed a strong counteracting influence on the SSV effect, the stray field effect. The sample containing Fe{sub 25}V{sub 75} alloy layers, has the highest ratio of Cooper pair coherence length and superconductor thickness (ξ{sub S})/(d{sub S}), and its superconducting transition temperature is comparable to the sample with Fe{sub 35}V{sub 65} alloy layers. Nevertheless, the SSV effect in sample Fe{sub 25}V{sub 75} with alloy layers is much smaller than in sample with Fe{sub 35}V{sub 65} alloy layers. For a high-performance superconducting spin valve based on a FM1/SC/FM2 heterostructure at least four parameters have to be optimized simultaneously. 1. The magnetic domain size in FM1 and FM2 has to be as large as possible in order to reduce the stray field effect resulting from magnetization components in the FM domain walls perpendicular to the SC layer. 2. When using ferromagnetic alloys as screening layers to suppress the stray field effect, the concentration of the ferromagnetic component in the alloy should be high enough to avoid the generation of non-magnetic/paramagnetic layers. Paramagnetic layers induce pair breaking, thus reducing the quantum-mechanical transparency T{sub F} for the Cooper pair wave function at the FM/SC interface. 3. Ferromagnetic alloys should be chosen as to achieve a better band structure match between the ferromagnetic component and the superconductor. Thereby, T{sub F} will be increased, augmenting the SSV effect. 4. The distance between FM1 and FM2, i.e. the thickness of the superconductor d{sub S}, should be of the order of the Cooper pair coherence length ξ{sub S} ∼ d{sub S}. Ideally, (ξ{sub S})/(d{sub S}) ∼ 1 or larger (see 125), since then the Cooper pair wave function is most effectively influenced by both magnetic layers FM1 and FM2. In the AFM/FM/SC/FM heterostructures, which we prepared according to these guidelines, we could observe satisfying switching characteristics, and SSV effects up to ΔT{sub S} = 20 mK. In this study we have verified the magnetic and superconducting properties of the unusual sample containing a [Fe(2ML)/V(180ML)] superlattice by means of conventional SQUID magnetometry as well as polarized neutron scattering (PNR) method. In the PNR we found a magnetic splitting in the PNR curves for the normal and superconducting state of the sample. Further we found weak indications for a reduction of the magnetic splitting beyond the error bars in the superconducting state compared to the normal conducting state of the sample, what can be considered as a weak indication of the Inverse Proximity effect. However, the measured spin asymmetry difference of the magnetic splitting between the superconducting and normal conducting state of the sample is not clear enough to give an unambiguous answer on the presence or absence of the inverse proximity effect.}
place = {Germany}
year = {2010}
month = {Dec}
}